path: root/doc/rfc/rfc3530.txt

Network Working Group                                         S. Shepler
Request for Comments: 3530                                  B. Callaghan
Obsoletes: 3010                                              D. Robinson
Category: Standards Track                                     R. Thurlow
                                                  Sun Microsystems, Inc.
                                                                C. Beame
                                                        Hummingbird Ltd.
                                                               M. Eisler
                                                               D. Noveck
                                                 Network Appliance, Inc.
                                                              April 2003


              Network File System (NFS) version 4 Protocol

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   The Network File System (NFS) version 4 is a distributed filesystem
   protocol which owes heritage to NFS protocol version 2, RFC 1094, and
   version 3, RFC 1813.  Unlike earlier versions, the NFS version 4
   protocol supports traditional file access while integrating support
   for file locking and the mount protocol.  In addition, support for
   strong security (and its negotiation), compound operations, client
   caching, and internationalization have been added.  Of course,
   attention has been applied to making NFS version 4 operate well in an
   Internet environment.

   This document replaces RFC 3010 as the definition of the NFS version
   4 protocol.

Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].




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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . .    8
        1.1.  Changes since RFC 3010 . . . . . . . . . . . . . . .    8
        1.2.  NFS version 4 Goals. . . . . . . . . . . . . . . . .    9
        1.3.  Inconsistencies of this Document with Section 18 . .    9
        1.4.  Overview of NFS version 4 Features . . . . . . . . .   10
              1.4.1.  RPC and Security . . . . . . . . . . . . . .   10
              1.4.2.  Procedure and Operation Structure. . . . . .   10
              1.4.3.  Filesystem Mode. . . . . . . . . . . . . . .   11
                      1.4.3.1.  Filehandle Types . . . . . . . . .   11
                      1.4.3.2.  Attribute Types. . . . . . . . . .   12
                      1.4.3.3.  Filesystem Replication and
                                Migration. . . . . . . . . . . . .   13
              1.4.4.  OPEN and CLOSE . . . . . . . . . . . . . . .   13
              1.4.5.  File locking . . . . . . . . . . . . . . . .   13
              1.4.6.  Client Caching and Delegation. . . . . . . .   13
        1.5.  General Definitions. . . . . . . . . . . . . . . . .   14
   2.   Protocol Data Types. . . . . . . . . . . . . . . . . . . .   16
        2.1.  Basic Data Types . . . . . . . . . . . . . . . . . .   16
        2.2.  Structured Data Types. . . . . . . . . . . . . . . .   18
   3.   RPC and Security Flavor. . . . . . . . . . . . . . . . . .   23
        3.1.  Ports and Transports . . . . . . . . . . . . . . . .   23
              3.1.1.  Client Retransmission Behavior . . . . . . .   24
        3.2.  Security Flavors . . . . . . . . . . . . . . . . . .   25
              3.2.1.  Security mechanisms for NFS version 4. . . .   25
                      3.2.1.1.  Kerberos V5 as a security triple .   25
                      3.2.1.2.  LIPKEY as a security triple. . . .   26
                      3.2.1.3.  SPKM-3 as a security triple. . . .   27
        3.3.  Security Negotiation . . . . . . . . . . . . . . . .   27
              3.3.1.  SECINFO. . . . . . . . . . . . . . . . . . .   28
              3.3.2.  Security Error . . . . . . . . . . . . . . .   28
        3.4.  Callback RPC Authentication. . . . . . . . . . . . .   28
   4.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . .   30
        4.1.  Obtaining the First Filehandle . . . . . . . . . . .   30
              4.1.1.  Root Filehandle. . . . . . . . . . . . . . .   31
              4.1.2.  Public Filehandle. . . . . . . . . . . . . .   31
        4.2.  Filehandle Types . . . . . . . . . . . . . . . . . .   31
              4.2.1.  General Properties of a Filehandle . . . . .   32
              4.2.2.  Persistent Filehandle. . . . . . . . . . . .   32
              4.2.3.  Volatile Filehandle. . . . . . . . . . . . .   33
              4.2.4.  One Method of Constructing a
                      Volatile Filehandle. . . . . . . . . . . . .   34
        4.3.  Client Recovery from Filehandle Expiration . . . . .   35
   5.   File Attributes. . . . . . . . . . . . . . . . . . . . . .   35
        5.1.  Mandatory Attributes . . . . . . . . . . . . . . . .   37
        5.2.  Recommended Attributes . . . . . . . . . . . . . . .   37
        5.3.  Named Attributes . . . . . . . . . . . . . . . . . .   37



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        5.4.  Classification of Attributes . . . . . . . . . . . .   38
        5.5.  Mandatory Attributes - Definitions . . . . . . . . .   39
        5.6.  Recommended Attributes - Definitions . . . . . . . .   41
        5.7.  Time Access. . . . . . . . . . . . . . . . . . . . .   46
        5.8.  Interpreting owner and owner_group . . . . . . . . .   47
        5.9.  Character Case Attributes. . . . . . . . . . . . . .   49
        5.10. Quota Attributes . . . . . . . . . . . . . . . . . .   49
        5.11. Access Control Lists . . . . . . . . . . . . . . . .   50
               5.11.1.  ACE type . . . . . . . . . . . . . . . . .   51
               5.11.2.  ACE Access Mask. . . . . . . . . . . . . .   52
               5.11.3.  ACE flag . . . . . . . . . . . . . . . . .   54
               5.11.4.  ACE who  . . . . . . . . . . . . . . . . .   55
               5.11.5.  Mode Attribute . . . . . . . . . . . . . .   56
               5.11.6.  Mode and ACL Attribute . . . . . . . . . .   57
               5.11.7.  mounted_on_fileid. . . . . . . . . . . . .   57
   6.  Filesystem Migration and Replication  . . . . . . . . . . .   58
        6.1.  Replication. . . . . . . . . . . . . . . . . . . . .   58
        6.2.  Migration. . . . . . . . . . . . . . . . . . . . . .   59
        6.3.  Interpretation of the fs_locations Attribute . . . .   60
        6.4.  Filehandle Recovery for Migration or Replication . .   61
   7.  NFS Server Name Space . . . . . . . . . . . . . . . . . . .   61
        7.1.  Server Exports . . . . . . . . . . . . . . . . . . .   61
        7.2.  Browsing Exports . . . . . . . . . . . . . . . . . .   62
        7.3.  Server Pseudo Filesystem . . . . . . . . . . . . . .   62
        7.4.  Multiple Roots . . . . . . . . . . . . . . . . . . .   63
        7.5.  Filehandle Volatility. . . . . . . . . . . . . . . .   63
        7.6.  Exported Root. . . . . . . . . . . . . . . . . . . .   63
        7.7.  Mount Point Crossing . . . . . . . . . . . . . . . .   63
        7.8.  Security Policy and Name Space Presentation. . . . .   64
   8.   File Locking and Share Reservations. . . . . . . . . . . .   65
        8.1.  Locking. . . . . . . . . . . . . . . . . . . . . . .   65
              8.1.1.    Client ID. . . . . . . . . . . . . . . . .   66
              8.1.2.    Server Release of Clientid . . . . . . . .   69
              8.1.3.    lock_owner and stateid Definition. . . . .   69
              8.1.4.    Use of the stateid and Locking . . . . . .   71
              8.1.5.    Sequencing of Lock Requests. . . . . . . .   73
              8.1.6.    Recovery from Replayed Requests. . . . . .   74
              8.1.7.    Releasing lock_owner State . . . . . . . .   74
              8.1.8.    Use of Open Confirmation . . . . . . . . .   75
        8.2.  Lock Ranges. . . . . . . . . . . . . . . . . . . . .   76
        8.3.  Upgrading and Downgrading Locks. . . . . . . . . . .   76
        8.4.  Blocking Locks . . . . . . . . . . . . . . . . . . .   77
        8.5.  Lease Renewal. . . . . . . . . . . . . . . . . . . .   77
        8.6.  Crash Recovery . . . . . . . . . . . . . . . . . . .   78
               8.6.1.   Client Failure and Recovery. . . . . . . .   79
               8.6.2.   Server Failure and Recovery. . . . . . . .   79
               8.6.3.   Network Partitions and Recovery. . . . . .   81
        8.7.   Recovery from a Lock Request Timeout or Abort . . .   85



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        8.8.   Server Revocation of Locks. . . . . . . . . . . . .   85
        8.9.   Share Reservations. . . . . . . . . . . . . . . . .   86
        8.10.  OPEN/CLOSE Operations . . . . . . . . . . . . . . .   87
               8.10.1.  Close and Retention of State
                        Information. . . . . . . . . . . . . . . .   88
        8.11.  Open Upgrade and Downgrade. . . . . . . . . . . . .   88
        8.12.  Short and Long Leases . . . . . . . . . . . . . . .   89
        8.13.  Clocks, Propagation Delay, and Calculating Lease
               Expiration. . . . . . . . . . . . . . . . . . . . .   89
        8.14.  Migration, Replication and State. . . . . . . . . .   90
               8.14.1.  Migration and State. . . . . . . . . . . .   90
               8.14.2.  Replication and State. . . . . . . . . . .   91
               8.14.3.  Notification of Migrated Lease . . . . . .   92
               8.14.4.  Migration and the Lease_time Attribute . .   92
   9.  Client-Side Caching . . . . . . . . . . . . . . . . . . . .   93
        9.1.   Performance Challenges for Client-Side Caching. . .   93
        9.2.   Delegation and Callbacks. . . . . . . . . . . . . .   94
               9.2.1.  Delegation Recovery . . . . . . . . . . . .   96
        9.3.   Data Caching. . . . . . . . . . . . . . . . . . . .   98
               9.3.1.   Data Caching and OPENs . . . . . . . . . .   98
               9.3.2.   Data Caching and File Locking. . . . . . .   99
               9.3.3.   Data Caching and Mandatory File Locking. .  101
               9.3.4.   Data Caching and File Identity . . . . . .  101
        9.4.   Open Delegation . . . . . . . . . . . . . . . . . .  102
               9.4.1.   Open Delegation and Data Caching . . . . .  104
               9.4.2.   Open Delegation and File Locks . . . . . .  106
               9.4.3.   Handling of CB_GETATTR . . . . . . . . . .  106
               9.4.4.   Recall of Open Delegation. . . . . . . . .  109
               9.4.5.   Clients that Fail to Honor
                        Delegation Recalls . . . . . . . . . . . .  111
               9.4.6.   Delegation Revocation. . . . . . . . . . .  112
        9.5.   Data Caching and Revocation . . . . . . . . . . . .  112
               9.5.1.   Revocation Recovery for Write Open
                        Delegation . . . . . . . . . . . . . . . .  113
        9.6.   Attribute Caching . . . . . . . . . . . . . . . . .  113
        9.7.   Data and Metadata Caching and Memory Mapped Files .  115
        9.8.   Name Caching  . . . . . . . . . . . . . . . . . . .  118
        9.9.   Directory Caching . . . . . . . . . . . . . . . . .  119
   10.  Minor Versioning . . . . . . . . . . . . . . . . . . . . .  120
   11.  Internationalization . . . . . . . . . . . . . . . . . . .  122
        11.1.  Stringprep profile for the utf8str_cs type. . . . .  123
               11.1.1.  Intended applicability of the
                        nfs4_cs_prep profile . . . . . . . . . . .  123
               11.1.2.  Character repertoire of nfs4_cs_prep . . .  124
               11.1.3.  Mapping used by nfs4_cs_prep . . . . . . .  124
               11.1.4.  Normalization used by nfs4_cs_prep . . . .  124
               11.1.5.  Prohibited output for nfs4_cs_prep . . . .  125
               11.1.6.  Bidirectional output for nfs4_cs_prep. . .  125



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        11.2.  Stringprep profile for the utf8str_cis type . . . .  125
               11.2.1.  Intended applicability of the
                        nfs4_cis_prep profile. . . . . . . . . . .  125
               11.2.2.  Character repertoire of nfs4_cis_prep  . .  125
               11.2.3.  Mapping used by nfs4_cis_prep  . . . . . .  125
               11.2.4.  Normalization used by nfs4_cis_prep  . . .  125
               11.2.5.  Prohibited output for nfs4_cis_prep  . . .  126
               11.2.6.  Bidirectional output for nfs4_cis_prep . .  126
        11.3.  Stringprep profile for the utf8str_mixed type . . .  126
               11.3.1.  Intended applicability of the
                        nfs4_mixed_prep profile. . . . . . . . . .  126
               11.3.2.  Character repertoire of nfs4_mixed_prep  .  126
               11.3.3.  Mapping used by nfs4_cis_prep  . . . . . .  126
               11.3.4.  Normalization used by nfs4_mixed_prep  . .  127
               11.3.5.  Prohibited output for nfs4_mixed_prep  . .  127
               11.3.6.  Bidirectional output for nfs4_mixed_prep .  127
        11.4.  UTF-8 Related Errors. . . . . . . . . . . . . . . .  127
   12.  Error Definitions  . . . . . . . . . . . . . . . . . . . .  128
   13.  NFS version 4 Requests . . . . . . . . . . . . . . . . . .  134
        13.1.  Compound Procedure. . . . . . . . . . . . . . . . .  134
        13.2.  Evaluation of a Compound Request. . . . . . . . . .  135
        13.3.  Synchronous Modifying Operations. . . . . . . . . .  136
        13.4.  Operation Values. . . . . . . . . . . . . . . . . .  136
   14.  NFS version 4 Procedures . . . . . . . . . . . . . . . . .  136
        14.1.  Procedure 0: NULL - No Operation. . . . . . . . . .  136
        14.2.  Procedure 1: COMPOUND - Compound Operations . . . .  137
               14.2.1.   Operation 3: ACCESS - Check Access
                         Rights. . . . . . . . . . . . . . . . . .  140
               14.2.2.   Operation 4: CLOSE - Close File . . . . .  142
               14.2.3.   Operation 5: COMMIT - Commit
                         Cached Data . . . . . . . . . . . . . . .  144
               14.2.4.   Operation 6: CREATE - Create a
                         Non-Regular File Object . . . . . . . . .  147
               14.2.5.   Operation 7: DELEGPURGE -
                         Purge Delegations Awaiting Recovery . . .  150
               14.2.6.   Operation 8: DELEGRETURN - Return
                         Delegation. . . . . . . . . . . . . . . .  151
               14.2.7.   Operation 9: GETATTR - Get Attributes . .  152
               14.2.8.   Operation 10: GETFH - Get Current
                         Filehandle. . . . . . . . . . . . . . . .  153
               14.2.9.   Operation 11: LINK - Create Link to a
                         File. . . . . . . . . . . . . . . . . . .  154
               14.2.10.  Operation 12: LOCK - Create Lock  . . . .  156
               14.2.11.  Operation 13: LOCKT - Test For Lock . . .  160
               14.2.12.  Operation 14: LOCKU - Unlock File . . . .  162
               14.2.13.  Operation 15: LOOKUP - Lookup Filename. .  163
               14.2.14.  Operation 16: LOOKUPP - Lookup
                         Parent Directory. . . . . . . . . . . . .  165



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               14.2.15.  Operation 17: NVERIFY - Verify
                         Difference in Attributes  . . . . . . . .  166
               14.2.16.  Operation 18: OPEN - Open a Regular
                         File. . . . . . . . . . . . . . . . . . .  168
               14.2.17.  Operation 19: OPENATTR - Open Named
                         Attribute Directory . . . . . . . . . . .  178
               14.2.18.  Operation 20: OPEN_CONFIRM -
                         Confirm Open . . . . . . . . . . . . . .   180
               14.2.19.  Operation 21: OPEN_DOWNGRADE -
                         Reduce Open File Access . . . . . . . . .  182
               14.2.20.  Operation 22: PUTFH - Set
                         Current Filehandle. . . . . . . . . . . .  184
               14.2.21.  Operation 23: PUTPUBFH -
                         Set Public Filehandle . . . . . . . . . .  185
               14.2.22.  Operation 24: PUTROOTFH -
                         Set Root Filehandle . . . . . . . . . . .  186
               14.2.23.  Operation 25: READ - Read from File . . .  187
               14.2.24.  Operation 26: READDIR -
                         Read Directory. . . . . . . . . . . . . .  190
               14.2.25.  Operation 27: READLINK -
                         Read Symbolic Link. . . . . . . . . . . .  193
               14.2.26.  Operation 28: REMOVE -
                         Remove Filesystem Object. . . . . . . . .  195
               14.2.27.  Operation 29: RENAME -
                         Rename Directory Entry. . . . . . . . . .  197
               14.2.28.  Operation 30: RENEW - Renew a Lease . . .  200
               14.2.29.  Operation 31: RESTOREFH -
                         Restore Saved Filehandle. . . . . . . . .  201
               14.2.30.  Operation 32: SAVEFH - Save
                         Current Filehandle. . . . . . . . . . . .  202
               14.2.31.  Operation 33: SECINFO - Obtain
                         Available Security. . . . . . . . . . . .  203
               14.2.32.  Operation 34: SETATTR - Set Attributes. .  206
               14.2.33.  Operation 35: SETCLIENTID -
                         Negotiate Clientid. . . . . . . . . . . .  209
               14.2.34.  Operation 36: SETCLIENTID_CONFIRM -
                         Confirm Clientid. . . . . . . . . . . . .  213
               14.2.35.  Operation 37: VERIFY -
                         Verify Same Attributes. . . . . . . . . .  217
               14.2.36.  Operation 38: WRITE - Write to File . . .  218
               14.2.37.  Operation 39: RELEASE_LOCKOWNER -
                         Release Lockowner State . . . . . . . . .  223
               14.2.38.  Operation 10044: ILLEGAL -
                         Illegal operation . . . . . . . . . . . .  224
   15.  NFS version 4 Callback Procedures  . . . . . . . . . . . .  225
        15.1.  Procedure 0: CB_NULL - No Operation . . . . . . . .  225
        15.2.  Procedure 1: CB_COMPOUND - Compound
               Operations. . . . . . . . . . . . . . . . . . . . .  226



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               15.2.1.  Operation 3: CB_GETATTR - Get
                        Attributes . . . . . . . . . . . . . . . .  228
               15.2.2.  Operation 4: CB_RECALL -
                        Recall an Open Delegation. . . . . . . . .  229
               15.2.3.  Operation 10044: CB_ILLEGAL -
                        Illegal Callback Operation . . . . . . . .  230
   16.  Security Considerations  . . . . . . . . . . . . . . . . .  231
   17.  IANA Considerations  . . . . . . . . . . . . . . . . . . .  232
        17.1.  Named Attribute Definition. . . . . . . . . . . . .  232
        17.2.  ONC RPC Network Identifiers (netids). . . . . . . .  232
   18.  RPC definition file  . . . . . . . . . . . . . . . . . . .  234
   19.  Acknowledgements . . . . . . . . . . . . . . . . . . . . .  268
   20.  Normative References . . . . . . . . . . . . . . . . . . .  268
   21.  Informative References . . . . . . . . . . . . . . . . . .  270
   22.  Authors' Information . . . . . . . . . . . . . . . . . . .  273
        22.1.  Editor's Address. . . . . . . . . . . . . . . . . .  273
        22.2.  Authors' Addresses. . . . . . . . . . . . . . . . .  274
   23.  Full Copyright Statement . . . . . . . . . . . . . . . . .  275

































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RFC 3530                 NFS version 4 Protocol               April 2003


1.  Introduction

1.1.  Changes since RFC 3010

   This definition of the NFS version 4 protocol replaces or obsoletes
   the definition present in [RFC3010].  While portions of the two
   documents have remained the same, there have been substantive changes
   in others.  The changes made between [RFC3010] and this document
   represent implementation experience and further review of the
   protocol.  While some modifications were made for ease of
   implementation or clarification, most updates represent errors or
   situations where the [RFC3010] definition were untenable.

   The following list is not all inclusive of all changes but presents
   some of the most notable changes or additions made:

   o  The state model has added an open_owner4 identifier.  This was
      done to accommodate Posix based clients and the model they use for
      file locking.  For Posix clients, an open_owner4 would correspond
      to a file descriptor potentially shared amongst a set of processes
      and the lock_owner4 identifier would correspond to a process that
      is locking a file.

   o  Clarifications and error conditions were added for the handling of
      the owner and group attributes.  Since these attributes are string
      based (as opposed to the numeric uid/gid of previous versions of
      NFS), translations may not be available and hence the changes
      made.

   o  Clarifications for the ACL and mode attributes to address
      evaluation and partial support.

   o  For identifiers that are defined as XDR opaque, limits were set on
      their size.

   o  Added the mounted_on_filed attribute to allow Posix clients to
      correctly construct local mounts.

   o  Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to deal
      correctly with confirmation details along with adding the ability
      to specify new client callback information.  Also added
      clarification of the callback information itself.

   o  Added a new operation LOCKOWNER_RELEASE to enable notifying the
      server that a lock_owner4 will no longer be used by the client.

   o  RENEW operation changes to identify the client correctly and allow
      for additional error returns.



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   o  Verify error return possibilities for all operations.

   o  Remove use of the pathname4 data type from LOOKUP and OPEN in
      favor of having the client construct a sequence of LOOKUP
      operations to achieive the same effect.

   o  Clarification of the internationalization issues and adoption of
      the new stringprep profile framework.

1.2.  NFS Version 4 Goals

   The NFS version 4 protocol is a further revision of the NFS protocol
   defined already by versions 2 [RFC1094] and 3 [RFC1813].  It retains
   the essential characteristics of previous versions: design for easy
   recovery, independent of transport protocols, operating systems and
   filesystems, simplicity, and good performance.  The NFS version 4
   revision has the following goals:

   o  Improved access and good performance on the Internet.

      The protocol is designed to transit firewalls easily, perform well
      where latency is high and bandwidth is low, and scale to very
      large numbers of clients per server.

   o  Strong security with negotiation built into the protocol.

      The protocol builds on the work of the ONCRPC working group in
      supporting the RPCSEC_GSS protocol.  Additionally, the NFS version
      4 protocol provides a mechanism to allow clients and servers the
      ability to negotiate security and require clients and servers to
      support a minimal set of security schemes.

   o  Good cross-platform interoperability.

      The protocol features a filesystem model that provides a useful,
      common set of features that does not unduly favor one filesystem
      or operating system over another.

   o  Designed for protocol extensions.

      The protocol is designed to accept standard extensions that do not
      compromise backward compatibility.

1.3.  Inconsistencies of this Document with Section 18

   Section 18, RPC Definition File, contains the definitions in XDR
   description language of the constructs used by the protocol.  Prior
   to Section 18, several of the constructs are reproduced for purposes



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   of explanation.  The reader is warned of the possibility of errors in
   the reproduced constructs outside of Section 18.  For any part of the
   document that is inconsistent with Section 18, Section 18 is to be
   considered authoritative.

1.4.  Overview of NFS version 4 Features

   To provide a reasonable context for the reader, the major features of
   NFS version 4 protocol will be reviewed in brief.  This will be done
   to provide an appropriate context for both the reader who is familiar
   with the previous versions of the NFS protocol and the reader that is
   new to the NFS protocols.  For the reader new to the NFS protocols,
   there is still a fundamental knowledge that is expected.  The reader
   should be familiar with the XDR and RPC protocols as described in
   [RFC1831] and [RFC1832].  A basic knowledge of filesystems and
   distributed filesystems is expected as well.

1.4.1.  RPC and Security

   As with previous versions of NFS, the External Data Representation
   (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
   version 4 protocol are those defined in [RFC1831] and [RFC1832].  To
   meet end to end security requirements, the RPCSEC_GSS framework
   [RFC2203] will be used to extend the basic RPC security.  With the
   use of RPCSEC_GSS, various mechanisms can be provided to offer
   authentication, integrity, and privacy to the NFS version 4 protocol.
   Kerberos V5 will be used as described in [RFC1964] to provide one
   security framework.  The LIPKEY GSS-API mechanism described in
   [RFC2847] will be used to provide for the use of user password and
   server public key by the NFS version 4 protocol.  With the use of
   RPCSEC_GSS, other mechanisms may also be specified and used for NFS
   version 4 security.

   To enable in-band security negotiation, the NFS version 4 protocol
   has added a new operation which provides the client a method of
   querying the server about its policies regarding which security
   mechanisms must be used for access to the server's filesystem
   resources.  With this, the client can securely match the security
   mechanism that meets the policies specified at both the client and
   server.

1.4.2.  Procedure and Operation Structure

   A significant departure from the previous versions of the NFS
   protocol is the introduction of the COMPOUND procedure.  For the NFS
   version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
   The COMPOUND procedure is defined in terms of operations and these
   operations correspond more closely to the traditional NFS procedures.



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   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical filesystem
   operations.  For example, without previous contact with a server a
   client will be able to read data from a file in one request by
   combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
   With previous versions of the NFS protocol, this type of single
   request was not possible.

   The model used for COMPOUND is very simple.  There is no logical OR
   or ANDing of operations.  The operations combined within a COMPOUND
   request are evaluated in order by the server.  Once an operation
   returns a failing result, the evaluation ends and the results of all
   evaluated operations are returned to the client.

   The NFS version 4 protocol continues to have the client refer to a
   file or directory at the server by a "filehandle".  The COMPOUND
   procedure has a method of passing a filehandle from one operation to
   another within the sequence of operations.  There is a concept of a
   "current filehandle" and "saved filehandle".  Most operations use the
   "current filehandle" as the filesystem object to operate upon.  The
   "saved filehandle" is used as temporary filehandle storage within a
   COMPOUND procedure as well as an additional operand for certain
   operations.

1.4.3.  Filesystem Model

   The general filesystem model used for the NFS version 4 protocol is
   the same as previous versions.  The server filesystem is hierarchical
   with the regular files contained within being treated as opaque byte
   streams.  In a slight departure, file and directory names are encoded
   with UTF-8 to deal with the basics of internationalization.

   The NFS version 4 protocol does not require a separate protocol to
   provide for the initial mapping between path name and filehandle.
   Instead of using the older MOUNT protocol for this mapping, the
   server provides a ROOT filehandle that represents the logical root or
   top of the filesystem tree provided by the server.  The server
   provides multiple filesystems by gluing them together with pseudo
   filesystems.  These pseudo filesystems provide for potential gaps in
   the path names between real filesystems.

1.4.3.1.  Filehandle Types

   In previous versions of the NFS protocol, the filehandle provided by
   the server was guaranteed to be valid or persistent for the lifetime
   of the filesystem object to which it referred.  For some server
   implementations, this persistence requirement has been difficult to



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   meet.  For the NFS version 4 protocol, this requirement has been
   relaxed by introducing another type of filehandle, volatile.  With
   persistent and volatile filehandle types, the server implementation
   can match the abilities of the filesystem at the server along with
   the operating environment.  The client will have knowledge of the
   type of filehandle being provided by the server and can be prepared
   to deal with the semantics of each.

1.4.3.2.  Attribute Types

   The NFS version 4 protocol introduces three classes of filesystem or
   file attributes.  Like the additional filehandle type, the
   classification of file attributes has been done to ease server
   implementations along with extending the overall functionality of the
   NFS protocol.  This attribute model is structured to be extensible
   such that new attributes can be introduced in minor revisions of the
   protocol without requiring significant rework.

   The three classifications are: mandatory, recommended and named
   attributes.  This is a significant departure from the previous
   attribute model used in the NFS protocol.  Previously, the attributes
   for the filesystem and file objects were a fixed set of mainly UNIX
   attributes.  If the server or client did not support a particular
   attribute, it would have to simulate the attribute the best it could.

   Mandatory attributes are the minimal set of file or filesystem
   attributes that must be provided by the server and must be properly
   represented by the server.  Recommended attributes represent
   different filesystem types and operating environments.  The
   recommended attributes will allow for better interoperability and the
   inclusion of more operating environments.  The mandatory and
   recommended attribute sets are traditional file or filesystem
   attributes.  The third type of attribute is the named attribute.  A
   named attribute is an opaque byte stream that is associated with a
   directory or file and referred to by a string name.  Named attributes
   are meant to be used by client applications as a method to associate
   application specific data with a regular file or directory.

   One significant addition to the recommended set of file attributes is
   the Access Control List (ACL) attribute.  This attribute provides for
   directory and file access control beyond the model used in previous
   versions of the NFS protocol.  The ACL definition allows for
   specification of user and group level access control.








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1.4.3.3.  Filesystem Replication and Migration

   With the use of a special file attribute, the ability to migrate or
   replicate server filesystems is enabled within the protocol.  The
   filesystem locations attribute provides a method for the client to
   probe the server about the location of a filesystem.  In the event of
   a migration of a filesystem, the client will receive an error when
   operating on the filesystem and it can then query as to the new file
   system location.  Similar steps are used for replication, the client
   is able to query the server for the multiple available locations of a
   particular filesystem.  From this information, the client can use its
   own policies to access the appropriate filesystem location.

1.4.4.  OPEN and CLOSE

   The NFS version 4 protocol introduces OPEN and CLOSE operations.  The
   OPEN operation provides a single point where file lookup, creation,
   and share semantics can be combined.  The CLOSE operation also
   provides for the release of state accumulated by OPEN.

1.4.5.  File locking

   With the NFS version 4 protocol, the support for byte range file
   locking is part of the NFS protocol.  The file locking support is
   structured so that an RPC callback mechanism is not required.  This
   is a departure from the previous versions of the NFS file locking
   protocol, Network Lock Manager (NLM).  The state associated with file
   locks is maintained at the server under a lease-based model.  The
   server defines a single lease period for all state held by a NFS
   client.  If the client does not renew its lease within the defined
   period, all state associated with the client's lease may be released
   by the server.  The client may renew its lease with use of the RENEW
   operation or implicitly by use of other operations (primarily READ).

1.4.6.  Client Caching and Delegation

   The file, attribute, and directory caching for the NFS version 4
   protocol is similar to previous versions.  Attributes and directory
   information are cached for a duration determined by the client.  At
   the end of a predefined timeout, the client will query the server to
   see if the related filesystem object has been updated.

   For file data, the client checks its cache validity when the file is
   opened.  A query is sent to the server to determine if the file has
   been changed.  Based on this information, the client determines if
   the data cache for the file should kept or released.  Also, when the
   file is closed, any modified data is written to the server.




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   If an application wants to serialize access to file data, file
   locking of the file data ranges in question should be used.

   The major addition to NFS version 4 in the area of caching is the
   ability of the server to delegate certain responsibilities to the
   client.  When the server grants a delegation for a file to a client,
   the client is guaranteed certain semantics with respect to the
   sharing of that file with other clients.  At OPEN, the server may
   provide the client either a read or write delegation for the file.
   If the client is granted a read delegation, it is assured that no
   other client has the ability to write to the file for the duration of
   the delegation.  If the client is granted a write delegation, the
   client is assured that no other client has read or write access to
   the file.

   Delegations can be recalled by the server.  If another client
   requests access to the file in such a way that the access conflicts
   with the granted delegation, the server is able to notify the initial
   client and recall the delegation.  This requires that a callback path
   exist between the server and client.  If this callback path does not
   exist, then delegations can not be granted.  The essence of a
   delegation is that it allows the client to locally service operations
   such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
   interaction with the server.

1.5.  General Definitions

   The following definitions are provided for the purpose of providing
   an appropriate context for the reader.


   Client    The "client" is the entity that accesses the NFS server's
             resources.  The client may be an application which contains
             the logic to access the NFS server directly.  The client
             may also be the traditional operating system client remote
             filesystem services for a set of applications.

             In the case of file locking the client is the entity that
             maintains a set of locks on behalf of one or more
             applications.  This client is responsible for crash or
             failure recovery for those locks it manages.

             Note that multiple clients may share the same transport and
             multiple clients may exist on the same network node.

   Clientid  A 64-bit quantity used as a unique, short-hand reference to
             a client supplied Verifier and ID.  The server is
             responsible for supplying the Clientid.



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   Lease     An interval of time defined by the server for which the
             client is irrevocably granted a lock.  At the end of a
             lease period the lock may be revoked if the lease has not
             been extended.  The lock must be revoked if a conflicting
             lock has been granted after the lease interval.

             All leases granted by a server have the same fixed
             interval.  Note that the fixed interval was chosen to
             alleviate the expense a server would have in maintaining
             state about variable length leases across server failures.

   Lock      The term "lock" is used to refer to both record (byte-
             range) locks as well as share reservations unless
             specifically stated otherwise.

   Server    The "Server" is the entity responsible for coordinating
             client access to a set of filesystems.

   Stable Storage
             NFS version 4 servers must be able to recover without data
             loss from multiple power failures (including cascading
             power failures, that is, several power failures in quick
             succession), operating system failures, and hardware
             failure of components other than the storage medium itself
             (for example, disk, nonvolatile RAM).

             Some examples of stable storage that are allowable for an
             NFS server include:

             1. Media commit of data, that is, the modified data has
                been successfully written to the disk media, for
                example, the disk platter.

             2. An immediate reply disk drive with battery-backed on-
                drive intermediate storage or uninterruptible power
                system (UPS).

             3. Server commit of data with battery-backed intermediate
                storage and recovery software.

             4. Cache commit with uninterruptible power system (UPS) and
                recovery software.

   Stateid   A 128-bit quantity returned by a server that uniquely
             defines the open and locking state provided by the server
             for a specific open or lock owner for a specific file.





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             Stateids composed of all bits 0 or all bits 1 have special
             meaning and are reserved values.

   Verifier  A 64-bit quantity generated by the client that the server
             can use to determine if the client has restarted and lost
             all previous lock state.

2.  Protocol Data Types

   The syntax and semantics to describe the data types of the NFS
   version 4 protocol are defined in the XDR [RFC1832] and RPC [RFC1831]
   documents.  The next sections build upon the XDR data types to define
   types and structures specific to this protocol.

2.1.  Basic Data Types

   Data Type       Definition
   ____________________________________________________________________
   int32_t         typedef int             int32_t;

   uint32_t        typedef unsigned int    uint32_t;

   int64_t         typedef hyper           int64_t;

   uint64_t        typedef unsigned hyper  uint64_t;

   attrlist4       typedef opaque        attrlist4<>;
                   Used for file/directory attributes

   bitmap4         typedef uint32_t        bitmap4<>;
                   Used in attribute array encoding.

   changeid4       typedef       uint64_t        changeid4;
                   Used in definition of change_info

   clientid4       typedef uint64_t        clientid4;
                   Shorthand reference to client identification

   component4      typedef utf8str_cs      component4;
                   Represents path name components

   count4          typedef uint32_t        count4;
                   Various count parameters (READ, WRITE, COMMIT)

   length4         typedef uint64_t        length4;
                   Describes LOCK lengths





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   linktext4       typedef utf8str_cs      linktext4;
                   Symbolic link contents

   mode4           typedef uint32_t        mode4;
                   Mode attribute data type

   nfs_cookie4     typedef uint64_t        nfs_cookie4;
                   Opaque cookie value for READDIR

   nfs_fh4         typedef opaque          nfs_fh4<NFS4_FHSIZE>;
                   Filehandle definition; NFS4_FHSIZE is defined as 128

   nfs_ftype4      enum nfs_ftype4;
                   Various defined file types

   nfsstat4        enum nfsstat4;
                   Return value for operations

   offset4         typedef uint64_t        offset4;
                   Various offset designations (READ, WRITE,
                   LOCK, COMMIT)

   pathname4       typedef component4      pathname4<>;
                   Represents path name for LOOKUP, OPEN and others

   qop4            typedef uint32_t        qop4;
                   Quality of protection designation in SECINFO

   sec_oid4        typedef opaque          sec_oid4<>;
                   Security Object Identifier
                   The sec_oid4 data type is not really opaque.
                   Instead contains an ASN.1 OBJECT IDENTIFIER as used
                   by GSS-API in the mech_type argument to
                   GSS_Init_sec_context.  See [RFC2743] for details.

   seqid4          typedef uint32_t        seqid4;
                   Sequence identifier used for file locking

   utf8string      typedef opaque          utf8string<>;
                   UTF-8 encoding for strings

   utf8str_cis     typedef opaque          utf8str_cis;
                   Case-insensitive UTF-8 string

   utf8str_cs      typedef opaque          utf8str_cs;
                   Case-sensitive UTF-8 string





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   utf8str_mixed   typedef opaque          utf8str_mixed;
                   UTF-8 strings with a case sensitive prefix and
                   a case insensitive suffix.

   verifier4       typedef opaque        verifier4[NFS4_VERIFIER_SIZE];
                   Verifier used for various operations (COMMIT,
                   CREATE, OPEN, READDIR, SETCLIENTID,
                   SETCLIENTID_CONFIRM, WRITE) NFS4_VERIFIER_SIZE is
                   defined as 8.

2.2.  Structured Data Types

   nfstime4
                  struct nfstime4 {
                          int64_t seconds;
                          uint32_t nseconds;
                  }

   The nfstime4 structure gives the number of seconds and nanoseconds
   since midnight or 0 hour January 1, 1970 Coordinated Universal Time
   (UTC).  Values greater than zero for the seconds field denote dates
   after the 0 hour January 1, 1970.  Values less than zero for the
   seconds field denote dates before the 0 hour January 1, 1970.  In
   both cases, the nseconds field is to be added to the seconds field
   for the final time representation.  For example, if the time to be
   represented is one-half second before 0 hour January 1, 1970, the
   seconds field would have a value of negative one (-1) and the
   nseconds fields would have a value of one-half second (500000000).
   Values greater than 999,999,999 for nseconds are considered invalid.

   This data type is used to pass time and date information.  A server
   converts to and from its local representation of time when processing
   time values, preserving as much accuracy as possible.  If the
   precision of timestamps stored for a filesystem object is less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is recommended to reduce client and server time skew.

   time_how4

                  enum time_how4 {
                          SET_TO_SERVER_TIME4 = 0,
                          SET_TO_CLIENT_TIME4 = 1
                  };








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   settime4

                  union settime4 switch (time_how4 set_it) {
                   case SET_TO_CLIENT_TIME4:
                           nfstime4       time;
                   default:
                           void;
                  };

   The above definitions are used as the attribute definitions to set
   time values.  If set_it is SET_TO_SERVER_TIME4, then the server uses
   its local representation of time for the time value.

   specdata4

                  struct specdata4 {
                          uint32_t specdata1; /* major device number */
                          uint32_t specdata2; /* minor device number */
                  };

   This data type represents additional information for the device file
   types NF4CHR and NF4BLK.

   fsid4

                  struct fsid4 {
                    uint64_t        major;
                    uint64_t        minor;
                  };

   This type is the filesystem identifier that is used as a mandatory
   attribute.

   fs_location4

                  struct fs_location4 {
                          utf8str_cis    server<>;
                          pathname4     rootpath;
                  };


   fs_locations4

                  struct fs_locations4 {
                          pathname4     fs_root;
                          fs_location4  locations<>;
                  };




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   The fs_location4 and fs_locations4 data types are used for the
   fs_locations recommended attribute which is used for migration and
   replication support.

   fattr4

                  struct fattr4 {
                          bitmap4       attrmask;
                          attrlist4     attr_vals;
                  };

   The fattr4 structure is used to represent file and directory
   attributes.

   The bitmap is a counted array of 32 bit integers used to contain bit
   values.  The position of the integer in the array that contains bit n
   can be computed from the expression (n / 32) and its bit within that
   integer is (n mod 32).

                           0            1
         +-----------+-----------+-----------+--
         |  count    | 31  ..  0 | 63  .. 32 |
         +-----------+-----------+-----------+--

   change_info4

                  struct change_info4 {
                          bool          atomic;
                          changeid4     before;
                          changeid4     after;
                  };

   This structure is used with the CREATE, LINK, REMOVE, RENAME
   operations to let the client know the value of the change attribute
   for the directory in which the target filesystem object resides.

   clientaddr4

                  struct clientaddr4 {
                          /* see struct rpcb in RFC 1833 */
                          string r_netid<>;    /* network id */
                          string r_addr<>;     /* universal address */
                  };

   The clientaddr4 structure is used as part of the SETCLIENTID
   operation to either specify the address of the client that is using a
   clientid or as part of the callback registration.  The




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   r_netid and r_addr fields are specified in [RFC1833], but they are
   underspecified in [RFC1833] as far as what they should look like for
   specific protocols.

   For TCP over IPv4 and for UDP over IPv4, the format of r_addr is the
   US-ASCII string:

      h1.h2.h3.h4.p1.p2

   The prefix, "h1.h2.h3.h4", is the standard textual form for
   representing an IPv4 address, which is always four octets long.
   Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
   the first through fourth octets each converted to ASCII-decimal.
   Assuming big-endian ordering, p1 and p2 are, respectively, the first
   and second octets each converted to ASCII-decimal.  For example, if a
   host, in big-endian order, has an address of 0x0A010307 and there is
   a service listening on, in big endian order, port 0x020F (decimal
   527), then the complete universal address is "10.1.3.7.2.15".

   For TCP over IPv4 the value of r_netid is the string "tcp".  For UDP
   over IPv4 the value of r_netid is the string "udp".

   For TCP over IPv6 and for UDP over IPv6, the format of r_addr is the
   US-ASCII string:

         x1:x2:x3:x4:x5:x6:x7:x8.p1.p2

   The suffix "p1.p2" is the service port, and is computed the same way
   as with universal addresses for TCP and UDP over IPv4.  The prefix,
   "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
   representing an IPv6 address as defined in Section 2.2 of [RFC2373].
   Additionally, the two alternative forms specified in Section 2.2 of
   [RFC2373] are also acceptable.

   For TCP over IPv6 the value of r_netid is the string "tcp6".  For UDP
   over IPv6 the value of r_netid is the string "udp6".

   cb_client4

                  struct cb_client4 {
                          unsigned int  cb_program;
                          clientaddr4   cb_location;
                  };

   This structure is used by the client to inform the server of its call
   back address; includes the program number and client address.





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   nfs_client_id4

                  struct nfs_client_id4 {
                          verifier4     verifier;
                          opaque        id<NFS4_OPAQUE_LIMIT>;
                  };

   This structure is part of the arguments to the SETCLIENTID operation.
   NFS4_OPAQUE_LIMIT is defined as 1024.

   open_owner4

                  struct open_owner4 {
                          clientid4     clientid;
                          opaque        owner<NFS4_OPAQUE_LIMIT>;
                  };

   This structure is used to identify the owner of open state.
   NFS4_OPAQUE_LIMIT is defined as 1024.

   lock_owner4

                  struct lock_owner4 {
                          clientid4     clientid;
                          opaque        owner<NFS4_OPAQUE_LIMIT>;
                  };

   This structure is used to identify the owner of file locking state.
   NFS4_OPAQUE_LIMIT is defined as 1024.

   open_to_lock_owner4

                  struct open_to_lock_owner4 {
                          seqid4          open_seqid;
                          stateid4        open_stateid;
                          seqid4          lock_seqid;
                          lock_owner4     lock_owner;
                  };

   This structure is used for the first LOCK operation done for an
   open_owner4.  It provides both the open_stateid and lock_owner such
   that the transition is made from a valid open_stateid sequence to
   that of the new lock_stateid sequence.  Using this mechanism avoids
   the confirmation of the lock_owner/lock_seqid pair since it is tied
   to established state in the form of the open_stateid/open_seqid.






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   stateid4

                  struct stateid4 {
                    uint32_t        seqid;
                    opaque          other[12];
                  };

   This structure is used for the various state sharing mechanisms
   between the client and server.  For the client, this data structure
   is read-only.  The starting value of the seqid field is undefined.
   The server is required to increment the seqid field monotonically at
   each transition of the stateid.  This is important since the client
   will inspect the seqid in OPEN stateids to determine the order of
   OPEN processing done by the server.

3.  RPC and Security Flavor

   The NFS version 4 protocol is a Remote Procedure Call (RPC)
   application that uses RPC version 2 and the corresponding eXternal
   Data Representation (XDR) as defined in [RFC1831] and [RFC1832].  The
   RPCSEC_GSS security flavor as defined in [RFC2203] MUST be used as
   the mechanism to deliver stronger security for the NFS version 4
   protocol.

3.1.  Ports and Transports

   Historically, NFS version 2 and version 3 servers have resided on
   port 2049.  The registered port 2049 [RFC3232] for the NFS protocol
   should be the default configuration.  Using the registered port for
   NFS services means the NFS client will not need to use the RPC
   binding protocols as described in [RFC1833]; this will allow NFS to
   transit firewalls.

   Where an NFS version 4 implementation supports operation over the IP
   network protocol, the supported transports between NFS and IP MUST be
   among the IETF-approved congestion control transport protocols, which
   include TCP and SCTP.  To enhance the possibilities for
   interoperability, an NFS version 4 implementation MUST support
   operation over the TCP transport protocol, at least until such time
   as a standards track RFC revises this requirement to use a different
   IETF-approved congestion control transport protocol.

   If TCP is used as the transport, the client and server SHOULD use
   persistent connections.  This will prevent the weakening of TCP's
   congestion control via short lived connections and will improve
   performance for the WAN environment by eliminating the need for SYN
   handshakes.




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   As noted in the Security Considerations section, the authentication
   model for NFS version 4 has moved from machine-based to principal-
   based.  However, this modification of the authentication model does
   not imply a technical requirement to move the TCP connection
   management model from whole machine-based to one based on a per user
   model.  In particular, NFS over TCP client implementations have
   traditionally multiplexed traffic for multiple users over a common
   TCP connection between an NFS client and server.  This has been true,
   regardless whether the NFS client is using AUTH_SYS, AUTH_DH,
   RPCSEC_GSS or any other flavor.  Similarly, NFS over TCP server
   implementations have assumed such a model and thus scale the
   implementation of TCP connection management in proportion to the
   number of expected client machines.  It is intended that NFS version
   4 will not modify this connection management model.  NFS version 4
   clients that violate this assumption can expect scaling issues on the
   server and hence reduced service.

   Note that for various timers, the client and server should avoid
   inadvertent synchronization of those timers.  For further discussion
   of the general issue refer to [Floyd].

3.1.1.  Client Retransmission Behavior

   When processing a request received over a reliable transport such as
   TCP, the NFS version 4 server MUST NOT silently drop the request,
   except if the transport connection has been broken.  Given such a
   contract between NFS version 4 clients and servers, clients MUST NOT
   retry a request unless one or both of the following are true:

   o  The transport connection has been broken

   o  The procedure being retried is the NULL procedure

   Since reliable transports, such as TCP, do not always synchronously
   inform a peer when the other peer has broken the connection (for
   example, when an NFS server reboots), the NFS version 4 client may
   want to actively "probe" the connection to see if has been broken.
   Use of the NULL procedure is one recommended way to do so.  So, when
   a client experiences a remote procedure call timeout (of some
   arbitrary implementation specific amount), rather than retrying the
   remote procedure call, it could instead issue a NULL procedure call
   to the server.  If the server has died, the transport connection
   break will eventually be indicated to the NFS version 4 client.  The
   client can then reconnect, and then retry the original request.  If
   the NULL procedure call gets a response, the connection has not
   broken.  The client can decide to wait longer for the original
   request's response, or it can break the transport connection and
   reconnect before re-sending the original request.



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   For callbacks from the server to the client, the same rules apply,
   but the server doing the callback becomes the client, and the client
   receiving the callback becomes the server.

3.2.  Security Flavors

   Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
   AUTH_DH, and AUTH_KRB4 as security flavors.  With [RFC2203] an
   additional security flavor of RPCSEC_GSS has been introduced which
   uses the functionality of GSS-API [RFC2743].  This allows for the use
   of various security mechanisms by the RPC layer without the
   additional implementation overhead of adding RPC security flavors.
   For NFS version 4, the RPCSEC_GSS security flavor MUST be used to
   enable the mandatory security mechanism.  Other flavors, such as,
   AUTH_NONE, AUTH_SYS, and AUTH_DH MAY be implemented as well.

3.2.1.  Security mechanisms for NFS version 4

   The use of RPCSEC_GSS requires selection of: mechanism, quality of
   protection, and service (authentication, integrity, privacy).  The
   remainder of this document will refer to these three parameters of
   the RPCSEC_GSS security as the security triple.

3.2.1.1.  Kerberos V5 as a security triple

   The Kerberos V5 GSS-API mechanism as described in [RFC1964] MUST be
   implemented and provide the following security triples.

   column descriptions:

   1 == number of pseudo flavor
   2 == name of pseudo flavor
   3 == mechanism's OID
   4 == mechanism's algorithm(s)
   5 == RPCSEC_GSS service

   1      2     3                    4             5
   --------------------------------------------------------------------
   390003 krb5  1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_none
   390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_integrity
   390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5   rpc_gss_svc_privacy
                                     for integrity,
                                     and 56 bit DES
                                     for privacy.

   Note that the pseudo flavor is presented here as a mapping aid to the
   implementor.  Because this NFS protocol includes a method to
   negotiate security and it understands the GSS-API mechanism, the



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   pseudo flavor is not needed.  The pseudo flavor is needed for NFS
   version 3 since the security negotiation is done via the MOUNT
   protocol.

   For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
   see [RFC2623].

   Users and implementors are warned that 56 bit DES is no longer
   considered state of the art in terms of resistance to brute force
   attacks.  Once a revision to [RFC1964] is available that adds support
   for AES, implementors are urged to incorporate AES into their NFSv4
   over Kerberos V5 protocol stacks, and users are similarly urged to
   migrate to the use of AES.

3.2.1.2.  LIPKEY as a security triple

   The LIPKEY GSS-API mechanism as described in [RFC2847] MUST be
   implemented and provide the following security triples.  The
   definition of the columns matches the previous subsection "Kerberos
   V5 as security triple"

   1      2        3                   4              5
   --------------------------------------------------------------------
   390006 lipkey   1.3.6.1.5.5.9       negotiated  rpc_gss_svc_none
   390007 lipkey-i 1.3.6.1.5.5.9       negotiated  rpc_gss_svc_integrity
   390008 lipkey-p 1.3.6.1.5.5.9       negotiated  rpc_gss_svc_privacy

   The mechanism algorithm is listed as "negotiated".  This is because
   LIPKEY is layered on SPKM-3 and in SPKM-3 [RFC2847] the
   confidentiality and integrity algorithms are negotiated.  Since
   SPKM-3 specifies HMAC-MD5 for integrity as MANDATORY, 128 bit
   cast5CBC for confidentiality for privacy as MANDATORY, and further
   specifies that HMAC-MD5 and cast5CBC MUST be listed first before
   weaker algorithms, specifying "negotiated" in column 4 does not
   impair interoperability.  In the event an SPKM-3 peer does not
   support the mandatory algorithms, the other peer is free to accept or
   reject the GSS-API context creation.

   Because SPKM-3 negotiates the algorithms, subsequent calls to
   LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
   of protection value of 0 (zero).  See section 5.2 of [RFC2025] for an
   explanation.

   LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
   name and password from the client to the server.  Once the user name
   and password have been accepted by the server, calls to the LIPKEY
   context are redirected to the SPKM-3 context.  See [RFC2847] for more
   details.



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3.2.1.3.  SPKM-3 as a security triple

   The SPKM-3 GSS-API mechanism as described in [RFC2847] MUST be
   implemented and provide the following security triples.  The
   definition of the columns matches the previous subsection "Kerberos
   V5 as security triple".

   1      2        3                   4              5
   --------------------------------------------------------------------
   390009 spkm3    1.3.6.1.5.5.1.3     negotiated  rpc_gss_svc_none
   390010 spkm3i   1.3.6.1.5.5.1.3     negotiated  rpc_gss_svc_integrity
   390011 spkm3p   1.3.6.1.5.5.1.3     negotiated  rpc_gss_svc_privacy

   For a discussion as to why the mechanism algorithm is listed as
   "negotiated", see the previous section "LIPKEY as a security triple."

   Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
   3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
   protection value of 0 (zero).  See section 5.2 of [RFC2025] for an
   explanation.

   Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
   mandatory set of triples to handle the situations where the initiator
   (the client) is anonymous or where the initiator has its own
   certificate.  If the initiator is anonymous, there will not be a user
   name and password to send to the target (the server).  If the
   initiator has its own certificate, then using passwords is
   superfluous.

3.3.  Security Negotiation

   With the NFS version 4 server potentially offering multiple security
   mechanisms, the client needs a method to determine or negotiate which
   mechanism is to be used for its communication with the server.  The
   NFS server may have multiple points within its filesystem name space
   that are available for use by NFS clients.  In turn the NFS server
   may be configured such that each of these entry points may have
   different or multiple security mechanisms in use.

   The security negotiation between client and server must be done with
   a secure channel to eliminate the possibility of a third party
   intercepting the negotiation sequence and forcing the client and
   server to choose a lower level of security than required or desired.
   See the section "Security Considerations" for further discussion.







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3.3.1.  SECINFO

   The new SECINFO operation will allow the client to determine, on a
   per filehandle basis, what security triple is to be used for server
   access.  In general, the client will not have to use the SECINFO
   operation except during initial communication with the server or when
   the client crosses policy boundaries at the server.  It is possible
   that the server's policies change during the client's interaction
   therefore forcing the client to negotiate a new security triple.

3.3.2.  Security Error

   Based on the assumption that each NFS version 4 client and server
   must support a minimum set of security (i.e., LIPKEY, SPKM-3, and
   Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
   communication with the server with one of the minimal security
   triples.  During communication with the server, the client may
   receive an NFS error of NFS4ERR_WRONGSEC.  This error allows the
   server to notify the client that the security triple currently being
   used is not appropriate for access to the server's filesystem
   resources.  The client is then responsible for determining what
   security triples are available at the server and choose one which is
   appropriate for the client.  See the section for the "SECINFO"
   operation for further discussion of how the client will respond to
   the NFS4ERR_WRONGSEC error and use SECINFO.

3.4.  Callback RPC Authentication

   Except as noted elsewhere in this section, the callback RPC
   (described later) MUST mutually authenticate the NFS server to the
   principal that acquired the clientid (also described later), using
   the security flavor the original SETCLIENTID operation used.

   For AUTH_NONE, there are no principals, so this is a non-issue.

   AUTH_SYS has no notions of mutual authentication or a server
   principal, so the callback from the server simply uses the AUTH_SYS
   credential that the user used when he set up the delegation.

   For AUTH_DH, one commonly used convention is that the server uses the
   credential corresponding to this AUTH_DH principal:

         unix.host@domain

   where host and domain are variables corresponding to the name of
   server host and directory services domain in which it lives such as a
   Network Information System domain or a DNS domain.




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   Because LIPKEY is layered over SPKM-3, it is permissible for the
   server to use SPKM-3 and not LIPKEY for the callback even if the
   client used LIPKEY for SETCLIENTID.

   Regardless of what security mechanism under RPCSEC_GSS is being used,
   the NFS server, MUST identify itself in GSS-API via a
   GSS_C_NT_HOSTBASED_SERVICE name type.  GSS_C_NT_HOSTBASED_SERVICE
   names are of the form:

         service@hostname

   For NFS, the "service" element is

         nfs

   Implementations of security mechanisms will convert nfs@hostname to
   various different forms.  For Kerberos V5 and LIPKEY, the following
   form is RECOMMENDED:

         nfs/hostname

   For Kerberos V5, nfs/hostname would be a server principal in the
   Kerberos Key Distribution Center database.  This is the same
   principal the client acquired a GSS-API context for when it issued
   the SETCLIENTID operation, therefore, the realm name for the server
   principal must be the same for the callback as it was for the
   SETCLIENTID.

   For LIPKEY, this would be the username passed to the target (the NFS
   version 4 client that receives the callback).

   It should be noted that LIPKEY may not work for callbacks, since the
   LIPKEY client uses a user id/password.  If the NFS client receiving
   the callback can authenticate the NFS server's user name/password
   pair, and if the user that the NFS server is authenticating to has a
   public key certificate, then it works.

   In situations where the NFS client uses LIPKEY and uses a per-host
   principal for the SETCLIENTID operation, instead of using LIPKEY for
   SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
   be used.  This effectively means that the client will use a
   certificate to authenticate and identify the initiator to the target
   on the NFS server.  Using SPKM-3 and not LIPKEY has the following
   advantages:

   o  When the server does a callback, it must authenticate to the
      principal used in the SETCLIENTID.  Even if LIPKEY is used,
      because LIPKEY is layered over SPKM-3, the NFS client will need to



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      have a certificate that corresponds to the principal used in the
      SETCLIENTID operation.  From an administrative perspective, having
      a user name, password, and certificate for both the client and
      server is redundant.

   o  LIPKEY was intended to minimize additional infrastructure
      requirements beyond a certificate for the target, and the
      expectation is that existing password infrastructure can be
      leveraged for the initiator.  In some environments, a per-host
      password does not exist yet.  If certificates are used for any
      per-host principals, then additional password infrastructure is
      not needed.

   o  In cases when a host is both an NFS client and server, it can
      share the same per-host certificate.

4.  Filehandles

   The filehandle in the NFS protocol is a per server unique identifier
   for a filesystem object.  The contents of the filehandle are opaque
   to the client.  Therefore, the server is responsible for translating
   the filehandle to an internal representation of the filesystem
   object.

4.1.  Obtaining the First Filehandle

   The operations of the NFS protocol are defined in terms of one or
   more filehandles.  Therefore, the client needs a filehandle to
   initiate communication with the server.  With the NFS version 2
   protocol [RFC1094] and the NFS version 3 protocol [RFC1813], there
   exists an ancillary protocol to obtain this first filehandle.  The
   MOUNT protocol, RPC program number 100005, provides the mechanism of
   translating a string based filesystem path name to a filehandle which
   can then be used by the NFS protocols.

   The MOUNT protocol has deficiencies in the area of security and use
   via firewalls.  This is one reason that the use of the public
   filehandle was introduced in [RFC2054] and [RFC2055].  With the use
   of the public filehandle in combination with the LOOKUP operation in
   the NFS version 2 and 3 protocols, it has been demonstrated that the
   MOUNT protocol is unnecessary for viable interaction between NFS
   client and server.

   Therefore, the NFS version 4 protocol will not use an ancillary
   protocol for translation from string based path names to a
   filehandle.  Two special filehandles will be used as starting points
   for the NFS client.




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4.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the filesystem name space
   at the NFS server.  The client uses or starts with the ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle to the
   ROOT of the server's file tree.  Once this PUTROOTFH operation is
   used, the client can then traverse the entirety of the server's file
   tree with the LOOKUP operation.  A complete discussion of the server
   name space is in the section "NFS Server Name Space".

4.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may be bound or represent an
   arbitrary filesystem object at the server.  The server is responsible
   for this binding.  It may be that the PUBLIC filehandle and the ROOT
   filehandle refer to the same filesystem object.  However, it is up to
   the administrative software at the server and the policies of the
   server administrator to define the binding of the PUBLIC filehandle
   and server filesystem object.  The client may not make any
   assumptions about this binding.  The client uses the PUBLIC
   filehandle via the PUTPUBFH operation.

4.2.  Filehandle Types

   In the NFS version 2 and 3 protocols, there was one type of
   filehandle with a single set of semantics.  This type of filehandle
   is termed "persistent" in NFS Version 4.  The semantics of a
   persistent filehandle remain the same as before.  A new type of
   filehandle introduced in NFS Version 4 is the "volatile" filehandle,
   which attempts to accommodate certain server environments.

   The volatile filehandle type was introduced to address server
   functionality or implementation issues which make correct
   implementation of a persistent filehandle infeasible.  Some server
   environments do not provide a filesystem level invariant that can be
   used to construct a persistent filehandle.  The underlying server
   filesystem may not provide the invariant or the server's filesystem
   programming interfaces may not provide access to the needed
   invariant.  Volatile filehandles may ease the implementation of
   server functionality such as hierarchical storage management or
   filesystem reorganization or migration.  However, the volatile
   filehandle increases the implementation burden for the client.






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   Since the client will need to handle persistent and volatile
   filehandles differently, a file attribute is defined which may be
   used by the client to determine the filehandle types being returned
   by the server.

4.2.1.  General Properties of a Filehandle

   The filehandle contains all the information the server needs to
   distinguish an individual file.  To the client, the filehandle is
   opaque.  The client stores filehandles for use in a later request and
   can compare two filehandles from the same server for equality by
   doing a byte-by-byte comparison.  However, the client MUST NOT
   otherwise interpret the contents of filehandles.  If two filehandles
   from the same server are equal, they MUST refer to the same file.
   Servers SHOULD try to maintain a one-to-one correspondence between
   filehandles and files but this is not required.  Clients MUST use
   filehandle comparisons only to improve performance, not for correct
   behavior.  All clients need to be prepared for situations in which it
   cannot be determined whether two filehandles denote the same object
   and in such cases, avoid making invalid assumptions which might cause
   incorrect behavior.  Further discussion of filehandle and attribute
   comparison in the context of data caching is presented in the section
   "Data Caching and File Identity".

   As an example, in the case that two different path names when
   traversed at the server terminate at the same filesystem object, the
   server SHOULD return the same filehandle for each path.  This can
   occur if a hard link is used to create two file names which refer to
   the same underlying file object and associated data.  For example, if
   paths /a/b/c and /a/d/c refer to the same file, the server SHOULD
   return the same filehandle for both path names traversals.

4.2.2.  Persistent Filehandle

   A persistent filehandle is defined as having a fixed value for the
   lifetime of the filesystem object to which it refers.  Once the
   server creates the filehandle for a filesystem object, the server
   MUST accept the same filehandle for the object for the lifetime of
   the object.  If the server restarts or reboots the NFS server must
   honor the same filehandle value as it did in the server's previous
   instantiation.  Similarly, if the filesystem is migrated, the new NFS
   server must honor the same filehandle as the old NFS server.

   The persistent filehandle will be become stale or invalid when the
   filesystem object is removed.  When the server is presented with a
   persistent filehandle that refers to a deleted object, it MUST return
   an error of NFS4ERR_STALE.  A filehandle may become stale when the
   filesystem containing the object is no longer available.  The file



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   system may become unavailable if it exists on removable media and the
   media is no longer available at the server or the filesystem in whole
   has been destroyed or the filesystem has simply been removed from the
   server's name space (i.e., unmounted in a UNIX environment).

4.2.3.  Volatile Filehandle

   A volatile filehandle does not share the same longevity
   characteristics of a persistent filehandle.  The server may determine
   that a volatile filehandle is no longer valid at many different
   points in time.  If the server can definitively determine that a
   volatile filehandle refers to an object that has been removed, the
   server should return NFS4ERR_STALE to the client (as is the case for
   persistent filehandles).  In all other cases where the server
   determines that a volatile filehandle can no longer be used, it
   should return an error of NFS4ERR_FHEXPIRED.

   The mandatory attribute "fh_expire_type" is used by the client to
   determine what type of filehandle the server is providing for a
   particular filesystem.  This attribute is a bitmask with the
   following values:

   FH4_PERSISTENT
             The value of FH4_PERSISTENT is used to indicate a
             persistent filehandle, which is valid until the object is
             removed from the filesystem.  The server will not return
             NFS4ERR_FHEXPIRED for this filehandle.  FH4_PERSISTENT is
             defined as a value in which none of the bits specified
             below are set.

   FH4_VOLATILE_ANY
             The filehandle may expire at any time, except as
             specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).

   FH4_NOEXPIRE_WITH_OPEN
             May only be set when FH4_VOLATILE_ANY is set.  If this bit
             is set, then the meaning of FH4_VOLATILE_ANY is qualified
             to exclude any expiration of the filehandle when it is
             open.

   FH4_VOL_MIGRATION
             The filehandle will expire as a result of migration.  If
             FH4_VOL_ANY is set, FH4_VOL_MIGRATION is redundant.








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   FH4_VOL_RENAME
             The filehandle will expire during rename.  This includes a
             rename by the requesting client or a rename by any other
             client.  If FH4_VOL_ANY is set, FH4_VOL_RENAME is
             redundant.

   Servers which provide volatile filehandles that may expire while open
   (i.e., if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
   FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN not set), should
   deny a RENAME or REMOVE that would affect an OPEN file of any of the
   components leading to the OPEN file.  In addition, the server should
   deny all RENAME or REMOVE requests during the grace period upon
   server restart.

   Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
   client to determine that expiration has occurred whenever a specific
   event occurs, without an explicit filehandle expiration error from
   the server.  FH4_VOL_ANY does not provide this form of information.
   In situations where the server will expire many, but not all
   filehandles upon migration (e.g., all but those that are open),
   FH4_VOLATILE_ANY (in this case with FH4_NOEXPIRE_WITH_OPEN) is a
   better choice since the client may not assume that all filehandles
   will expire when migration occurs, and it is likely that additional
   expirations will occur (as a result of file CLOSE) that are separated
   in time from the migration event itself.

4.2.4.  One Method of Constructing a Volatile Filehandle

   A volatile filehandle, while opaque to the client could contain:

   [volatile bit = 1 | server boot time | slot | generation number]

   o  slot is an index in the server volatile filehandle table

   o  generation number is the generation number for the table
      entry/slot

   When the client presents a volatile filehandle, the server makes the
   following checks, which assume that the check for the volatile bit
   has passed.  If the server boot time is less than the current server
   boot time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
   NFS4ERR_BADHANDLE.  If the generation number does not match, return
   NFS4ERR_FHEXPIRED.

   When the server reboots, the table is gone (it is volatile).

   If volatile bit is 0, then it is a persistent filehandle with a
   different structure following it.



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4.3.  Client Recovery from Filehandle Expiration

   If possible, the client SHOULD recover from the receipt of an
   NFS4ERR_FHEXPIRED error.  The client must take on additional
   responsibility so that it may prepare itself to recover from the
   expiration of a volatile filehandle.  If the server returns
   persistent filehandles, the client does not need these additional
   steps.

   For volatile filehandles, most commonly the client will need to store
   the component names leading up to and including the filesystem object
   in question.  With these names, the client should be able to recover
   by finding a filehandle in the name space that is still available or
   by starting at the root of the server's filesystem name space.

   If the expired filehandle refers to an object that has been removed
   from the filesystem, obviously the client will not be able to recover
   from the expired filehandle.

   It is also possible that the expired filehandle refers to a file that
   has been renamed.  If the file was renamed by another client, again
   it is possible that the original client will not be able to recover.
   However, in the case that the client itself is renaming the file and
   the file is open, it is possible that the client may be able to
   recover.  The client can determine the new path name based on the
   processing of the rename request.  The client can then regenerate the
   new filehandle based on the new path name.  The client could also use
   the compound operation mechanism to construct a set of operations
   like:
           RENAME A B
           LOOKUP B
           GETFH

   Note that the COMPOUND procedure does not provide atomicity.  This
   example only reduces the overhead of recovering from an expired
   filehandle.

5.  File Attributes

   To meet the requirements of extensibility and increased
   interoperability with non-UNIX platforms, attributes must be handled
   in a flexible manner.  The NFS version 3 fattr3 structure contains a
   fixed list of attributes that not all clients and servers are able to
   support or care about.  The fattr3 structure can not be extended as
   new needs arise and it provides no way to indicate non-support.  With
   the NFS version 4 protocol, the client is able query what attributes
   the server supports and construct requests with only those supported
   attributes (or a subset thereof).



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   To this end, attributes are divided into three groups: mandatory,
   recommended, and named.  Both mandatory and recommended attributes
   are supported in the NFS version 4 protocol by a specific and well-
   defined encoding and are identified by number.  They are requested by
   setting a bit in the bit vector sent in the GETATTR request; the
   server response includes a bit vector to list what attributes were
   returned in the response.  New mandatory or recommended attributes
   may be added to the NFS protocol between major revisions by
   publishing a standards-track RFC which allocates a new attribute
   number value and defines the encoding for the attribute.  See the
   section "Minor Versioning" for further discussion.

   Named attributes are accessed by the new OPENATTR operation, which
   accesses a hidden directory of attributes associated with a file
   system object.  OPENATTR takes a filehandle for the object and
   returns the filehandle for the attribute hierarchy.  The filehandle
   for the named attributes is a directory object accessible by LOOKUP
   or READDIR and contains files whose names represent the named
   attributes and whose data bytes are the value of the attribute.  For
   example:

      LOOKUP     "foo"       ; look up file
      GETATTR    attrbits
      OPENATTR               ; access foo's named attributes
      LOOKUP     "x11icon"   ; look up specific attribute
      READ       0,4096      ; read stream of bytes

   Named attributes are intended for data needed by applications rather
   than by an NFS client implementation.  NFS implementors are strongly
   encouraged to define their new attributes as recommended attributes
   by bringing them to the IETF standards-track process.

   The set of attributes which are classified as mandatory is
   deliberately small since servers must do whatever it takes to support
   them.  A server should support as many of the recommended attributes
   as possible but by their definition, the server is not required to
   support all of them.  Attributes are deemed mandatory if the data is
   both needed by a large number of clients and is not otherwise
   reasonably computable by the client when support is not provided on
   the server.

   Note that the hidden directory returned by OPENATTR is a convenience
   for protocol processing.  The client should not make any assumptions
   about the server's implementation of named attributes and whether the
   underlying filesystem at the server has a named attribute directory
   or not.  Therefore, operations such as SETATTR and GETATTR on the
   named attribute directory are undefined.




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5.1.  Mandatory Attributes

   These MUST be supported by every NFS version 4 client and server in
   order to ensure a minimum level of interoperability.  The server must
   store and return these attributes and the client must be able to
   function with an attribute set limited to these attributes.  With
   just the mandatory attributes some client functionality may be
   impaired or limited in some ways.  A client may ask for any of these
   attributes to be returned by setting a bit in the GETATTR request and
   the server must return their value.

5.2.  Recommended Attributes

   These attributes are understood well enough to warrant support in the
   NFS version 4 protocol.  However, they may not be supported on all
   clients and servers.  A client may ask for any of these attributes to
   be returned by setting a bit in the GETATTR request but must handle
   the case where the server does not return them.  A client may ask for
   the set of attributes the server supports and should not request
   attributes the server does not support.  A server should be tolerant
   of requests for unsupported attributes and simply not return them
   rather than considering the request an error.  It is expected that
   servers will support all attributes they comfortably can and only
   fail to support attributes which are difficult to support in their
   operating environments.  A server should provide attributes whenever
   they don't have to "tell lies" to the client.  For example, a file
   modification time should be either an accurate time or should not be
   supported by the server.  This will not always be comfortable to
   clients but the client is better positioned decide whether and how to
   fabricate or construct an attribute or whether to do without the
   attribute.

5.3.  Named Attributes

   These attributes are not supported by direct encoding in the NFS
   Version 4 protocol but are accessed by string names rather than
   numbers and correspond to an uninterpreted stream of bytes which are
   stored with the filesystem object.  The name space for these
   attributes may be accessed by using the OPENATTR operation.  The
   OPENATTR operation returns a filehandle for a virtual "attribute
   directory" and further perusal of the name space may be done using
   READDIR and LOOKUP operations on this filehandle.  Named attributes
   may then be examined or changed by normal READ and WRITE and CREATE
   operations on the filehandles returned from READDIR and LOOKUP.
   Named attributes may have attributes.






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   It is recommended that servers support arbitrary named attributes.  A
   client should not depend on the ability to store any named attributes
   in the server's filesystem.  If a server does support named
   attributes, a client which is also able to handle them should be able
   to copy a file's data and meta-data with complete transparency from
   one location to another; this would imply that names allowed for
   regular directory entries are valid for named attribute names as
   well.

   Names of attributes will not be controlled by this document or other
   IETF standards track documents.  See the section "IANA
   Considerations" for further discussion.

5.4.  Classification of Attributes

   Each of the Mandatory and Recommended attributes can be classified in
   one of three categories: per server, per filesystem, or per
   filesystem object.  Note that it is possible that some per filesystem
   attributes may vary within the filesystem.  See the "homogeneous"
   attribute for its definition.  Note that the attributes
   time_access_set and time_modify_set are not listed in this section
   because they are write-only attributes corresponding to time_access
   and time_modify, and are used in a special instance of SETATTR.

   o  The per server attribute is:

         lease_time

   o  The per filesystem attributes are:

      supp_attr, fh_expire_type, link_support, symlink_support,
      unique_handles, aclsupport, cansettime, case_insensitive,
      case_preserving, chown_restricted, files_avail, files_free,
      files_total, fs_locations, homogeneous, maxfilesize, maxname,
      maxread, maxwrite, no_trunc, space_avail, space_free, space_total,
      time_delta

   o  The per filesystem object attributes are:

      type, change, size, named_attr, fsid, rdattr_error, filehandle,
      ACL, archive, fileid, hidden, maxlink, mimetype, mode, numlinks,
      owner, owner_group, rawdev, space_used, system, time_access,
      time_backup, time_create, time_metadata, time_modify,
      mounted_on_fileid

   For quota_avail_hard, quota_avail_soft, and quota_used see their
   definitions below for the appropriate classification.




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5.5.  Mandatory Attributes - Definitions

   Name              #    DataType     Access   Description
   ___________________________________________________________________
   supp_attr         0    bitmap       READ     The bit vector which
                                                would retrieve all
                                                mandatory and
                                                recommended attributes
                                                that are supported for
                                                this object.  The
                                                scope of this
                                                attribute applies to
                                                all objects with a
                                                matching fsid.

   type              1    nfs4_ftype   READ     The type of the object
                                                (file, directory,
                                                symlink, etc.)

   fh_expire_type    2    uint32       READ     Server uses this to
                                                specify filehandle
                                                expiration behavior to
                                                the client.  See the
                                                section "Filehandles"
                                                for additional
                                                description.

   change            3    uint64       READ     A value created by the
                                                server that the client
                                                can use to determine
                                                if file data,
                                                directory contents or
                                                attributes of the
                                                object have been
                                                modified.  The server
                                                may return the
                                                object's time_metadata
                                                attribute for this
                                                attribute's value but
                                                only if the filesystem
                                                object can not be
                                                updated more
                                                frequently than the
                                                resolution of
                                                time_metadata.

   size              4    uint64       R/W      The size of the object
                                                in bytes.



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   link_support      5    bool         READ     True, if the object's
                                                filesystem supports
                                                hard links.

   symlink_support   6    bool         READ     True, if the object's
                                                filesystem supports
                                                symbolic links.

   named_attr        7    bool         READ     True, if this object
                                                has named attributes.
                                                In other words, object
                                                has a non-empty named
                                                attribute directory.

   fsid              8    fsid4        READ     Unique filesystem
                                                identifier for the
                                                filesystem holding
                                                this object.  fsid
                                                contains major and
                                                minor components each
                                                of which are uint64.

   unique_handles    9    bool         READ     True, if two distinct
                                                filehandles guaranteed
                                                to refer to two
                                                different filesystem
                                                objects.

   lease_time        10   nfs_lease4   READ     Duration of leases at
                                                server in seconds.

   rdattr_error      11   enum         READ     Error returned from
                                                getattr during
                                                readdir.

   filehandle        19   nfs_fh4      READ     The filehandle of this
                                                object (primarily for
                                                readdir requests).













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5.6.  Recommended Attributes - Definitions

   Name                #    Data Type      Access   Description
   _____________________________________________________________________
   ACL                 12   nfsace4<>      R/W      The access control
                                                    list for the object.

   aclsupport          13   uint32         READ     Indicates what types
                                                    of ACLs are
                                                    supported on the
                                                    current filesystem.

   archive             14   bool           R/W      True, if this file
                                                    has been archived
                                                    since the time of
                                                    last modification
                                                    (deprecated in favor
                                                    of time_backup).

   cansettime          15   bool           READ     True, if the server
                                                    is able to change
                                                    the times for a
                                                    filesystem object as
                                                    specified in a
                                                    SETATTR operation.

   case_insensitive    16   bool           READ     True, if filename
                                                    comparisons on this
                                                    filesystem are case
                                                    insensitive.

   case_preserving     17   bool           READ     True, if filename
                                                    case on this
                                                    filesystem are
                                                    preserved.

   chown_restricted    18   bool           READ     If TRUE, the server
                                                    will reject any
                                                    request to change
                                                    either the owner or
                                                    the group associated
                                                    with a file if the
                                                    caller is not a
                                                    privileged user (for
                                                    example, "root" in
                                                    UNIX operating
                                                    environments or in
                                                    Windows 2000 the



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                                                    "Take Ownership"
                                                    privilege).

   fileid              20   uint64         READ     A number uniquely
                                                    identifying the file
                                                    within the
                                                    filesystem.

   files_avail         21   uint64         READ     File slots available
                                                    to this user on the
                                                    filesystem
                                                    containing this
                                                    object - this should
                                                    be the smallest
                                                    relevant limit.

   files_free          22   uint64         READ     Free file slots on
                                                    the filesystem
                                                    containing this
                                                    object - this should
                                                    be the smallest
                                                    relevant limit.

   files_total         23   uint64         READ     Total file slots on
                                                    the filesystem
                                                    containing this
                                                    object.

   fs_locations        24   fs_locations   READ     Locations where this
                                                    filesystem may be
                                                    found.  If the
                                                    server returns
                                                    NFS4ERR_MOVED
                                                    as an error, this
                                                    attribute MUST be
                                                    supported.

   hidden              25   bool           R/W      True, if the file is
                                                    considered hidden
                                                    with respect to the
                                                    Windows API.

   homogeneous         26   bool           READ     True, if this
                                                    object's filesystem
                                                    is homogeneous,
                                                    i.e., are per
                                                    filesystem
                                                    attributes the same



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                                                    for all filesystem's
                                                    objects?

   maxfilesize         27   uint64         READ     Maximum supported
                                                    file size for the
                                                    filesystem of this
                                                    object.

   maxlink             28   uint32         READ     Maximum number of
                                                    links for this
                                                    object.

   maxname             29   uint32         READ     Maximum filename
                                                    size supported for
                                                    this object.

   maxread             30   uint64         READ     Maximum read size
                                                    supported for this
                                                    object.

   maxwrite            31   uint64         READ     Maximum write size
                                                    supported for this
                                                    object.  This
                                                    attribute SHOULD be
                                                    supported if the
                                                    file is writable.
                                                    Lack of this
                                                    attribute can
                                                    lead to the client
                                                    either wasting
                                                    bandwidth or not
                                                    receiving the best
                                                    performance.

   mimetype            32   utf8<>         R/W      MIME body
                                                    type/subtype of this
                                                    object.

   mode                33   mode4          R/W      UNIX-style mode and
                                                    permission bits for
                                                    this object.

   no_trunc            34   bool           READ     True, if a name
                                                    longer than name_max
                                                    is used, an error be
                                                    returned and name is
                                                    not truncated.




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   numlinks            35   uint32         READ     Number of hard links
                                                    to this object.

   owner               36   utf8<>         R/W      The string name of
                                                    the owner of this
                                                    object.

   owner_group         37   utf8<>         R/W      The string name of
                                                    the group ownership
                                                    of this object.

   quota_avail_hard    38   uint64         READ     For definition see
                                                    "Quota Attributes"
                                                    section below.

   quota_avail_soft    39   uint64         READ     For definition see
                                                    "Quota Attributes"
                                                    section below.

   quota_used          40   uint64         READ     For definition see
                                                    "Quota Attributes"
                                                    section below.

   rawdev              41   specdata4      READ     Raw device
                                                    identifier.  UNIX
                                                    device major/minor
                                                    node information.
                                                    If the value of
                                                    type is not
                                                    NF4BLK or NF4CHR,
                                                    the value return
                                                    SHOULD NOT be
                                                    considered useful.

   space_avail         42   uint64         READ     Disk space in bytes
                                                    available to this
                                                    user on the
                                                    filesystem
                                                    containing this
                                                    object - this should
                                                    be the smallest
                                                    relevant limit.

   space_free          43   uint64         READ     Free disk space in
                                                    bytes on the
                                                    filesystem
                                                    containing this
                                                    object - this should



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                                                    be the smallest
                                                    relevant limit.

   space_total         44   uint64         READ     Total disk space in
                                                    bytes on the
                                                    filesystem
                                                    containing this
                                                    object.

   space_used          45   uint64         READ     Number of filesystem
                                                    bytes allocated to
                                                    this object.

   system              46   bool           R/W      True, if this file
                                                    is a "system" file
                                                    with respect to the
                                                    Windows API.

   time_access         47   nfstime4       READ     The time of last
                                                    access to the object
                                                    by a read that was
                                                    satisfied by the
                                                    server.

   time_access_set     48   settime4       WRITE    Set the time of last
                                                    access to the
                                                    object.  SETATTR
                                                    use only.

   time_backup         49   nfstime4       R/W      The time of last
                                                    backup of the
                                                    object.

   time_create         50   nfstime4       R/W      The time of creation
                                                    of the object.  This
                                                    attribute does not
                                                    have any relation to
                                                    the traditional UNIX
                                                    file attribute
                                                    "ctime" or "change
                                                    time".

   time_delta          51   nfstime4       READ     Smallest useful
                                                    server time
                                                    granularity.






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   time_metadata       52   nfstime4       READ     The time of last
                                                    meta-data
                                                    modification of the
                                                    object.

   time_modify         53   nfstime4       READ     The time of last
                                                    modification to the
                                                    object.

   time_modify_set     54   settime4       WRITE    Set the time of last
                                                    modification to the
                                                    object.  SETATTR use
                                                    only.

   mounted_on_fileid   55   uint64         READ     Like fileid, but if
                                                    the target
                                                    filehandle is the
                                                    root of a filesystem
                                                    return the fileid of
                                                    the underlying
                                                    directory.

5.7.  Time Access

   As defined above, the time_access attribute represents the time of
   last access to the object by a read that was satisfied by the server.
   The notion of what is an "access" depends on server's operating
   environment and/or the server's filesystem semantics.  For example,
   for servers obeying POSIX semantics, time_access would be updated
   only by the READLINK, READ, and READDIR operations and not any of the
   operations that modify the content of the object.  Of course, setting
   the corresponding time_access_set attribute is another way to modify
   the time_access attribute.

   Whenever the file object resides on a writable filesystem, the server
   should make best efforts to record time_access into stable storage.
   However, to mitigate the performance effects of doing so, and most
   especially whenever the server is satisfying the read of the object's
   content from its cache, the server MAY cache access time updates and
   lazily write them to stable storage.  It is also acceptable to give
   administrators of the server the option to disable time_access
   updates.









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5.8.  Interpreting owner and owner_group

   The recommended attributes "owner" and "owner_group" (and also users
   and groups within the "acl" attribute) are represented in terms of a
   UTF-8 string.  To avoid a representation that is tied to a particular
   underlying implementation at the client or server, the use of the
   UTF-8 string has been chosen.  Note that section 6.1 of [RFC2624]
   provides additional rationale.  It is expected that the client and
   server will have their own local representation of owner and
   owner_group that is used for local storage or presentation to the end
   user.  Therefore, it is expected that when these attributes are
   transferred between the client and server that the local
   representation is translated to a syntax of the form
   "user@dns_domain".  This will allow for a client and server that do
   not use the same local representation the ability to translate to a
   common syntax that can be interpreted by both.

   Similarly, security principals may be represented in different ways
   by different security mechanisms.  Servers normally translate these
   representations into a common format, generally that used by local
   storage, to serve as a means of identifying the users corresponding
   to these security principals.  When these local identifiers are
   translated to the form of the owner attribute, associated with files
   created by such principals they identify, in a common format, the
   users associated with each corresponding set of security principals.

   The translation used to interpret owner and group strings is not
   specified as part of the protocol.  This allows various solutions to
   be employed.  For example, a local translation table may be consulted
   that maps between a numeric id to the user@dns_domain syntax.  A name
   service may also be used to accomplish the translation.  A server may
   provide a more general service, not limited by any particular
   translation (which would only translate a limited set of possible
   strings) by storing the owner and owner_group attributes in local
   storage without any translation or it may augment a translation
   method by storing the entire string for attributes for which no
   translation is available while using the local representation for
   those cases in which a translation is available.

   Servers that do not provide support for all possible values of the
   owner and owner_group attributes, should return an error
   (NFS4ERR_BADOWNER) when a string is presented that has no
   translation, as the value to be set for a SETATTR of the owner,
   owner_group, or acl attributes.  When a server does accept an owner
   or owner_group value as valid on a SETATTR (and similarly for the
   owner and group strings in an acl), it is promising to return that
   same string when a corresponding GETATTR is done.  Configuration
   changes and ill-constructed name translations (those that contain



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   aliasing) may make that promise impossible to honor.  Servers should
   make appropriate efforts to avoid a situation in which these
   attributes have their values changed when no real change to ownership
   has occurred.

   The "dns_domain" portion of the owner string is meant to be a DNS
   domain name.  For example, user@ietf.org.  Servers should accept as
   valid a set of users for at least one domain.  A server may treat
   other domains as having no valid translations.  A more general
   service is provided when a server is capable of accepting users for
   multiple domains, or for all domains, subject to security
   constraints.

   In the case where there is no translation available to the client or
   server, the attribute value must be constructed without the "@".
   Therefore, the absence of the @ from the owner or owner_group
   attribute signifies that no translation was available at the sender
   and that the receiver of the attribute should not use that string as
   a basis for translation into its own internal format.  Even though
   the attribute value can not be translated, it may still be useful.
   In the case of a client, the attribute string may be used for local
   display of ownership.

   To provide a greater degree of compatibility with previous versions
   of NFS (i.e., v2 and v3), which identified users and groups by 32-bit
   unsigned uid's and gid's, owner and group strings that consist of
   decimal numeric values with no leading zeros can be given a special
   interpretation by clients and servers which choose to provide such
   support.  The receiver may treat such a user or group string as
   representing the same user as would be represented by a v2/v3 uid or
   gid having the corresponding numeric value.  A server is not
   obligated to accept such a string, but may return an NFS4ERR_BADOWNER
   instead.  To avoid this mechanism being used to subvert user and
   group translation, so that a client might pass all of the owners and
   groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
   error when there is a valid translation for the user or owner
   designated in this way.  In that case, the client must use the
   appropriate name@domain string and not the special form for
   compatibility.

   The owner string "nobody" may be used to designate an anonymous user,
   which will be associated with a file created by a security principal
   that cannot be mapped through normal means to the owner attribute.








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5.9.  Character Case Attributes

   With respect to the case_insensitive and case_preserving attributes,
   each UCS-4 character (which UTF-8 encodes) has a "long descriptive
   name" [RFC1345] which may or may not included the word "CAPITAL" or
   "SMALL".  The presence of SMALL or CAPITAL allows an NFS server to
   implement unambiguous and efficient table driven mappings for case
   insensitive comparisons, and non-case-preserving storage.  For
   general character handling and internationalization issues, see the
   section "Internationalization".

5.10.  Quota Attributes

   For the attributes related to filesystem quotas, the following
   definitions apply:

   quota_avail_soft
         The value in bytes which represents the amount of additional
         disk space that can be allocated to this file or directory
         before the user may reasonably be warned.  It is understood
         that this space may be consumed by allocations to other files
         or directories though there is a rule as to which other files
         or directories.

   quota_avail_hard
         The value in bytes which represent the amount of additional
         disk space beyond the current allocation that can be allocated
         to this file or directory before further allocations will be
         refused.  It is understood that this space may be consumed by
         allocations to other files or directories.

   quota_used
         The value in bytes which represent the amount of disc space
         used by this file or directory and possibly a number of other
         similar files or directories, where the set of "similar" meets
         at least the criterion that allocating space to any file or
         directory in the set will reduce the "quota_avail_hard" of
         every other file or directory in the set.

         Note that there may be a number of distinct but overlapping
         sets of files or directories for which a quota_used value is
         maintained (e.g., "all files with a given owner", "all files
         with a given group owner", etc.).

         The server is at liberty to choose any of those sets but should
         do so in a repeatable way.  The rule may be configured per-
         filesystem or may be "choose the set with the smallest quota".




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5.11.  Access Control Lists

   The NFS version 4 ACL attribute is an array of access control entries
   (ACE).  Although, the client can read and write the ACL attribute,
   the NFSv4 model is the server does all access control based on the
   server's interpretation of the ACL.  If at any point the client wants
   to check access without issuing an operation that modifies or reads
   data or metadata, the client can use the OPEN and ACCESS operations
   to do so.  There are various access control entry types, as defined
   in the Section "ACE type".  The server is able to communicate which
   ACE types are supported by returning the appropriate value within the
   aclsupport attribute.  Each ACE covers one or more operations on a
   file or directory as described in the Section "ACE Access Mask".  It
   may also contain one or more flags that modify the semantics of the
   ACE as defined in the Section "ACE flag".

   The NFS ACE attribute is defined as follows:

         typedef uint32_t        acetype4;
         typedef uint32_t        aceflag4;
         typedef uint32_t        acemask4;

         struct nfsace4 {
                 acetype4        type;
                 aceflag4        flag;
                 acemask4        access_mask;
                 utf8str_mixed   who;
         };

   To determine if a request succeeds, each nfsace4 entry is processed
   in order by the server.  Only ACEs which have a "who" that matches
   the requester are considered.  Each ACE is processed until all of the
   bits of the requester's access have been ALLOWED.  Once a bit (see
   below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
   considered in the processing of later ACEs.  If an ACCESS_DENIED_ACE
   is encountered where the requester's access still has unALLOWED bits
   in common with the "access_mask" of the ACE, the request is denied.
   However, unlike the ALLOWED and DENIED ACE types, the ALARM and AUDIT
   ACE types do not affect a requester's access, and instead are for
   triggering events as a result of a requester's access attempt.

   Therefore, all AUDIT and ALARM ACEs are processed until end of the
   ACL.  When the ACL is fully processed, if there are bits in
   requester's mask that have not been considered whether the server
   allows or denies the access is undefined.  If there is a mode
   attribute on the file, then this cannot happen, since the mode's
   MODE4_*OTH bits will map to EVERYONE@ ACEs that unambiguously specify
   the requester's access.



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   The NFS version 4 ACL model is quite rich.  Some server platforms may
   provide access control functionality that goes beyond the UNIX-style
   mode attribute, but which is not as rich as the NFS ACL model.  So
   that users can take advantage of this more limited functionality, the
   server may indicate that it supports ACLs as long as it follows the
   guidelines for mapping between its ACL model and the NFS version 4
   ACL model.

   The situation is complicated by the fact that a server may have
   multiple modules that enforce ACLs.  For example, the enforcement for
   NFS version 4 access may be different from the enforcement for local
   access, and both may be different from the enforcement for access
   through other protocols such as SMB.  So it may be useful for a
   server to accept an ACL even if not all of its modules are able to
   support it.

   The guiding principle in all cases is that the server must not accept
   ACLs that appear to make the file more secure than it really is.

5.11.1.  ACE type

   Type         Description
   _____________________________________________________
   ALLOW        Explicitly grants the access defined in
                acemask4 to the file or directory.

   DENY         Explicitly denies the access defined in
                acemask4 to the file or directory.

   AUDIT        LOG (system dependent) any access
                attempt to a file or directory which
                uses any of the access methods specified
                in acemask4.

   ALARM        Generate a system ALARM (system
                dependent) when any access attempt is
                made to a file or directory for the
                access methods specified in acemask4.

   A server need not support all of the above ACE types.  The bitmask
   constants used to represent the above definitions within the

   aclsupport attribute are as follows:

      const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
      const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
      const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
      const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;



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   The semantics of the "type" field follow the descriptions provided
   above.

   The constants used for the type field (acetype4) are as follows:

      const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
      const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
      const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
      const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;

   Clients should not attempt to set an ACE unless the server claims
   support for that ACE type.  If the server receives a request to set
   an ACE that it cannot store, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.  If the server receives a request to set an ACE
   that it can store but cannot enforce, the server SHOULD reject the
   request with NFS4ERR_ATTRNOTSUPP.

   Example: suppose a server can enforce NFS ACLs for NFS access but
   cannot enforce ACLs for local access.  If arbitrary processes can run
   on the server, then the server SHOULD NOT indicate ACL support.  On
   the other hand, if only trusted administrative programs run locally,
   then the server may indicate ACL support.

5.11.2.  ACE Access Mask

   The access_mask field contains values based on the following:

   Access                 Description
   _______________________________________________________________
   READ_DATA              Permission to read the data of the file
   LIST_DIRECTORY         Permission to list the contents of a
                          directory
   WRITE_DATA             Permission to modify the file's data
   ADD_FILE               Permission to add a new file to a
                          directory
   APPEND_DATA            Permission to append data to a file
   ADD_SUBDIRECTORY       Permission to create a subdirectory to a
                          directory
   READ_NAMED_ATTRS       Permission to read the named attributes
                          of a file
   WRITE_NAMED_ATTRS      Permission to write the named attributes
                          of a file
   EXECUTE                Permission to execute a file
   DELETE_CHILD           Permission to delete a file or directory
                          within a directory
   READ_ATTRIBUTES        The ability to read basic attributes
                          (non-acls) of a file
   WRITE_ATTRIBUTES       Permission to change basic attributes



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                          (non-acls) of a file
   DELETE                 Permission to Delete the file
   READ_ACL               Permission to Read the ACL
   WRITE_ACL              Permission to Write the ACL
   WRITE_OWNER            Permission to change the owner
   SYNCHRONIZE            Permission to access file locally at the
                          server with synchronous reads and writes

   The bitmask constants used for the access mask field are as follows:

   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   Server implementations need not provide the granularity of control
   that is implied by this list of masks.  For example, POSIX-based
   systems might not distinguish APPEND_DATA (the ability to append to a
   file) from WRITE_DATA (the ability to modify existing contents); both
   masks would be tied to a single "write" permission.  When such a
   server returns attributes to the client, it would show both
   APPEND_DATA and WRITE_DATA if and only if the write permission is
   enabled.

   If a server receives a SETATTR request that it cannot accurately
   implement, it should error in the direction of more restricted
   access.  For example, suppose a server cannot distinguish overwriting
   data from appending new data, as described in the previous paragraph.
   If a client submits an ACE where APPEND_DATA is set but WRITE_DATA is
   not (or vice versa), the server should reject the request with
   NFS4ERR_ATTRNOTSUPP.  Nonetheless, if the ACE has type DENY, the
   server may silently turn on the other bit, so that both APPEND_DATA
   and WRITE_DATA are denied.





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5.11.3.  ACE flag

   The "flag" field contains values based on the following descriptions.

   ACE4_FILE_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new non-directory file created.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new directory created.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory,
      only to newly created files/directories as specified by the above
      two flags.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  Normally when a new directory is
      created and an ACE exists on the parent directory which is marked
      ACL4_DIRECTORY_INHERIT_ACE, two ACEs are placed on the new
      directory.  One for the directory itself and one which is an
      inheritable ACE for newly created directories.  This flag tells
      the server to not place an ACE on the newly created directory
      which is inheritable by subdirectories of the created directory.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

   ACL4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits relate only to
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during the processing of the file's ACL,
      the server encounters an AUDIT or ALARM ACE that matches the
      principal attempting the OPEN, the server notes that fact, and the
      presence, if any, of the SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
      processing, and the share reservation processing, and the OPEN
      call, it then notes if the OPEN succeeded or failed.  If the OPEN
      succeeded, and if the SUCCESS flag was set for a matching AUDIT or
      ALARM, then the appropriate AUDIT or ALARM event occurs.  If the
      OPEN failed, and if the FAILED flag was set for the matching AUDIT
      or ALARM, then the appropriate AUDIT or ALARM event occurs.
      Clearly either or both of the SUCCESS or FAILED can be set, but if
      neither is set, the AUDIT or ALARM ACE is not useful.






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      The previously described processing applies to that of the ACCESS
      operation as well.  The difference being that "success" or
      "failure" does not mean whether ACCESS returns NFS4_OK or not.
      Success means whether ACCESS returns all requested and supported
      bits.  Failure means whether ACCESS failed to return a bit that
      was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to a GROUP as defined under UNIX.

   The bitmask constants used for the flag field are as follows:

   const ACE4_FILE_INHERIT_ACE             = 0x00000001;
   const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
   const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
   const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
   const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
   const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
   const ACE4_IDENTIFIER_GROUP             = 0x00000040;

   A server need not support any of these flags.  If the server supports
   flags that are similar to, but not exactly the same as, these flags,
   the implementation may define a mapping between the protocol-defined
   flags and the implementation-defined flags.  Again, the guiding
   principle is that the file not appear to be more secure than it
   really is.

   For example, suppose a client tries to set an ACE with
   ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.  If the
   server does not support any form of ACL inheritance, the server
   should reject the request with NFS4ERR_ATTRNOTSUPP.  If the server
   supports a single "inherit ACE" flag that applies to both files and
   directories, the server may reject the request (i.e., requiring the
   client to set both the file and directory inheritance flags).  The
   server may also accept the request and silently turn on the
   ACE4_DIRECTORY_INHERIT_ACE flag.

5.11.4.  ACE who

   There are several special identifiers ("who") which need to be
   understood universally, rather than in the context of a particular
   DNS domain.  Some of these identifiers cannot be understood when an
   NFS client accesses the server, but have meaning when a local process
   accesses the file.  The ability to display and modify these
   permissions is permitted over NFS, even if none of the access methods
   on the server understands the identifiers.





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   Who                    Description
   _______________________________________________________________
   "OWNER"                The owner of the file.
   "GROUP"                The group associated with the file.
   "EVERYONE"             The world.
   "INTERACTIVE"          Accessed from an interactive terminal.
   "NETWORK"              Accessed via the network.
   "DIALUP"               Accessed as a dialup user to the server.
   "BATCH"                Accessed from a batch job.
   "ANONYMOUS"            Accessed without any authentication.
   "AUTHENTICATED"        Any authenticated user (opposite of
                          ANONYMOUS)
   "SERVICE"              Access from a system service.

   To avoid conflict, these special identifiers are distinguish by an
   appended "@" and should appear in the form "xxxx@" (note: no domain
   name after the "@").  For example: ANONYMOUS@.

5.11.5.  Mode Attribute

   The NFS version 4 mode attribute is based on the UNIX mode bits.  The
   following bits are defined:

      const MODE4_SUID = 0x800;  /* set user id on execution */
      const MODE4_SGID = 0x400;  /* set group id on execution */
      const MODE4_SVTX = 0x200;  /* save text even after use */
      const MODE4_RUSR = 0x100;  /* read permission: owner */
      const MODE4_WUSR = 0x080;  /* write permission: owner */
      const MODE4_XUSR = 0x040;  /* execute permission: owner */
      const MODE4_RGRP = 0x020;  /* read permission: group */
      const MODE4_WGRP = 0x010;  /* write permission: group */
      const MODE4_XGRP = 0x008;  /* execute permission: group */
      const MODE4_ROTH = 0x004;  /* read permission: other */
      const MODE4_WOTH = 0x002;  /* write permission: other */
      const MODE4_XOTH = 0x001;  /* execute permission: other */

   Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
   identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and

   MODE4_XGRP apply to the principals identified in the owner_group
   attribute.  Bits MODE4_ROTH, MODE4_WOTH, MODE4_XOTH apply to any
   principal that does not match that in the owner group, and does not
   have a group matching that of the owner_group attribute.

   The remaining bits are not defined by this protocol and MUST NOT be
   used.  The minor version mechanism must be used to define further bit
   usage.




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   Note that in UNIX, if a file has the MODE4_SGID bit set and no
   MODE4_XGRP bit set, then READ and WRITE must use mandatory file
   locking.

5.11.6.  Mode and ACL Attribute

   The server that supports both mode and ACL must take care to
   synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
   ACEs which have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@" so that the client can see semantically equivalent access
   permissions exist whether the client asks for owner, owner_group and
   mode attributes, or for just the ACL.

   Because the mode attribute includes bits (e.g., MODE4_SVTX) that have
   nothing to do with ACL semantics, it is permitted for clients to
   specify both the ACL attribute and mode in the same SETATTR
   operation.  However, because there is no prescribed order for
   processing the attributes in a SETATTR, the client must ensure that
   ACL attribute, if specified without mode, would produce the desired
   mode bits, and conversely, the mode attribute if specified without
   ACL, would produce the desired "OWNER@", "GROUP@", and "EVERYONE@"
   ACEs.

5.11.7.  mounted_on_fileid

   UNIX-based operating environments connect a filesystem into the
   namespace by connecting (mounting) the filesystem onto the existing
   file object (the mount point, usually a directory) of an existing
   filesystem.  When the mount point's parent directory is read via an
   API like readdir(), the return results are directory entries, each
   with a component name and a fileid.  The fileid of the mount point's
   directory entry will be different from the fileid that the stat()
   system call returns.  The stat() system call is returning the fileid
   of the root of the mounted filesystem, whereas readdir() is returning
   the fileid stat() would have returned before any filesystems were
   mounted on the mount point.

   Unlike NFS version 3, NFS version 4 allows a client's LOOKUP request
   to cross other filesystems.  The client detects the filesystem
   crossing whenever the filehandle argument of LOOKUP has an fsid
   attribute different from that of the filehandle returned by LOOKUP.
   A UNIX-based client will consider this a "mount point crossing".
   UNIX has a legacy scheme for allowing a process to determine its
   current working directory.  This relies on readdir() of a mount
   point's parent and stat() of the mount point returning fileids as
   previously described.  The mounted_on_fileid attribute corresponds to
   the fileid that readdir() would have returned as described
   previously.



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   While the NFS version 4 client could simply fabricate a fileid
   corresponding to what mounted_on_fileid provides (and if the server
   does not support mounted_on_fileid, the client has no choice), there
   is a risk that the client will generate a fileid that conflicts with
   one that is already assigned to another object in the filesystem.
   Instead, if the server can provide the mounted_on_fileid, the
   potential for client operational problems in this area is eliminated.

   If the server detects that there is no mounted point at the target
   file object, then the value for mounted_on_fileid that it returns is
   the same as that of the fileid attribute.

   The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
   provide it if possible, and for a UNIX-based server, this is
   straightforward.  Usually, mounted_on_fileid will be requested during
   a READDIR operation, in which case it is trivial (at least for UNIX-
   based servers) to return mounted_on_fileid since it is equal to the
   fileid of a directory entry returned by readdir().  If
   mounted_on_fileid is requested in a GETATTR operation, the server
   should obey an invariant that has it returning a value that is equal
   to the file object's entry in the object's parent directory, i.e.,
   what readdir() would have returned.  Some operating environments
   allow a series of two or more filesystems to be mounted onto a single
   mount point.  In this case, for the server to obey the aforementioned
   invariant, it will need to find the base mount point, and not the
   intermediate mount points.

6.  Filesystem Migration and Replication

   With the use of the recommended attribute "fs_locations", the NFS
   version 4 server has a method of providing filesystem migration or
   replication services.  For the purposes of migration and replication,
   a filesystem will be defined as all files that share a given fsid
   (both major and minor values are the same).

   The fs_locations attribute provides a list of filesystem locations.
   These locations are specified by providing the server name (either
   DNS domain or IP address) and the path name representing the root of
   the filesystem.  Depending on the type of service being provided, the
   list will provide a new location or a set of alternate locations for
   the filesystem.  The client will use this information to redirect its
   requests to the new server.

6.1.  Replication

   It is expected that filesystem replication will be used in the case
   of read-only data.  Typically, the filesystem will be replicated on
   two or more servers.  The fs_locations attribute will provide the



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   list of these locations to the client.  On first access of the
   filesystem, the client should obtain the value of the fs_locations
   attribute.  If, in the future, the client finds the server
   unresponsive, the client may attempt to use another server specified
   by fs_locations.

   If applicable, the client must take the appropriate steps to recover
   valid filehandles from the new server.  This is described in more
   detail in the following sections.

6.2.  Migration

   Filesystem migration is used to move a filesystem from one server to
   another.  Migration is typically used for a filesystem that is
   writable and has a single copy.  The expected use of migration is for
   load balancing or general resource reallocation.  The protocol does
   not specify how the filesystem will be moved between servers.  This
   server-to-server transfer mechanism is left to the server
   implementor.  However, the method used to communicate the migration
   event between client and server is specified here.

   Once the servers participating in the migration have completed the
   move of the filesystem, the error NFS4ERR_MOVED will be returned for
   subsequent requests received by the original server.  The
   NFS4ERR_MOVED error is returned for all operations except PUTFH and
   GETATTR.  Upon receiving the NFS4ERR_MOVED error, the client will
   obtain the value of the fs_locations attribute.  The client will then
   use the contents of the attribute to redirect its requests to the
   specified server.  To facilitate the use of GETATTR, operations such
   as PUTFH must also be accepted by the server for the migrated file
   system's filehandles.  Note that if the server returns NFS4ERR_MOVED,
   the server MUST support the fs_locations attribute.

   If the client requests more attributes than just fs_locations, the
   server may return fs_locations only.  This is to be expected since
   the server has migrated the filesystem and may not have a method of
   obtaining additional attribute data.

   The server implementor needs to be careful in developing a migration
   solution.  The server must consider all of the state information
   clients may have outstanding at the server.  This includes but is not
   limited to locking/share state, delegation state, and asynchronous
   file writes which are represented by WRITE and COMMIT verifiers.  The
   server should strive to minimize the impact on its clients during and
   after the migration process.






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6.3.  Interpretation of the fs_locations Attribute

   The fs_location attribute is structured in the following way:

   struct fs_location {
           utf8str_cis     server<>;
           pathname4       rootpath;
   };

   struct fs_locations {
           pathname4       fs_root;
           fs_location     locations<>;
   };

   The fs_location struct is used to represent the location of a
   filesystem by providing a server name and the path to the root of the
   filesystem.  For a multi-homed server or a set of servers that use
   the same rootpath, an array of server names may be provided.  An
   entry in the server array is an UTF8 string and represents one of a
   traditional DNS host name, IPv4 address, or IPv6 address.  It is not
   a requirement that all servers that share the same rootpath be listed
   in one fs_location struct.  The array of server names is provided for
   convenience.  Servers that share the same rootpath may also be listed
   in separate fs_location entries in the fs_locations attribute.

   The fs_locations struct and attribute then contains an array of
   locations.  Since the name space of each server may be constructed
   differently, the "fs_root" field is provided.  The path represented
   by fs_root represents the location of the filesystem in the server's
   name space.  Therefore, the fs_root path is only associated with the
   server from which the fs_locations attribute was obtained.  The
   fs_root path is meant to aid the client in locating the filesystem at
   the various servers listed.

   As an example, there is a replicated filesystem located at two
   servers (servA and servB).  At servA the filesystem is located at
   path "/a/b/c".  At servB the filesystem is located at path "/x/y/z".
   In this example the client accesses the filesystem first at servA
   with a multi-component lookup path of "/a/b/c/d".  Since the client
   used a multi-component lookup to obtain the filehandle at "/a/b/c/d",
   it is unaware that the filesystem's root is located in servA's name
   space at "/a/b/c".  When the client switches to servB, it will need
   to determine that the directory it first referenced at servA is now
   represented by the path "/x/y/z/d" on servB.  To facilitate this, the
   fs_locations attribute provided by servA would have a fs_root value
   of "/a/b/c" and two entries in fs_location.  One entry in fs_location
   will be for itself (servA) and the other will be for servB with a




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   path of "/x/y/z".  With this information, the client is able to
   substitute "/x/y/z" for the "/a/b/c" at the beginning of its access
   path and construct "/x/y/z/d" to use for the new server.

   See the section "Security Considerations" for a discussion on the
   recommendations for the security flavor to be used by any GETATTR
   operation that requests the "fs_locations" attribute.

6.4.  Filehandle Recovery for Migration or Replication

   Filehandles for filesystems that are replicated or migrated generally
   have the same semantics as for filesystems that are not replicated or
   migrated.  For example, if a filesystem has persistent filehandles
   and it is migrated to another server, the filehandle values for the
   filesystem will be valid at the new server.

   For volatile filehandles, the servers involved likely do not have a
   mechanism to transfer filehandle format and content between
   themselves.  Therefore, a server may have difficulty in determining
   if a volatile filehandle from an old server should return an error of
   NFS4ERR_FHEXPIRED.  Therefore, the client is informed, with the use
   of the fh_expire_type attribute, whether volatile filehandles will
   expire at the migration or replication event.  If the bit
   FH4_VOL_MIGRATION is set in the fh_expire_type attribute, the client
   must treat the volatile filehandle as if the server had returned the
   NFS4ERR_FHEXPIRED error.  At the migration or replication event in
   the presence of the FH4_VOL_MIGRATION bit, the client will not
   present the original or old volatile filehandle to the new server.
   The client will start its communication with the new server by
   recovering its filehandles using the saved file names.

7.  NFS Server Name Space

7.1.  Server Exports

   On a UNIX server the name space describes all the files reachable by
   pathnames under the root directory or "/".  On a Windows NT server
   the name space constitutes all the files on disks named by mapped
   disk letters.  NFS server administrators rarely make the entire
   server's filesystem name space available to NFS clients.  More often
   portions of the name space are made available via an "export"
   feature.  In previous versions of the NFS protocol, the root
   filehandle for each export is obtained through the MOUNT protocol;
   the client sends a string that identifies the export of name space
   and the server returns the root filehandle for it.  The MOUNT
   protocol supports an EXPORTS procedure that will enumerate the
   server's exports.




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7.2.  Browsing Exports

   The NFS version 4 protocol provides a root filehandle that clients
   can use to obtain filehandles for these exports via a multi-component
   LOOKUP.  A common user experience is to use a graphical user
   interface (perhaps a file "Open" dialog window) to find a file via
   progressive browsing through a directory tree.  The client must be
   able to move from one export to another export via single-component,
   progressive LOOKUP operations.

   This style of browsing is not well supported by the NFS version 2 and
   3 protocols.  The client expects all LOOKUP operations to remain
   within a single server filesystem.  For example, the device attribute
   will not change.  This prevents a client from taking name space paths
   that span exports.

   An automounter on the client can obtain a snapshot of the server's
   name space using the EXPORTS procedure of the MOUNT protocol.  If it
   understands the server's pathname syntax, it can create an image of
   the server's name space on the client.  The parts of the name space
   that are not exported by the server are filled in with a "pseudo
   filesystem" that allows the user to browse from one mounted
   filesystem to another.  There is a drawback to this representation of
   the server's name space on the client: it is static.  If the server
   administrator adds a new export the client will be unaware of it.

7.3.  Server Pseudo Filesystem

   NFS version 4 servers avoid this name space inconsistency by
   presenting all the exports within the framework of a single server
   name space.  An NFS version 4 client uses LOOKUP and READDIR
   operations to browse seamlessly from one export to another.  Portions
   of the server name space that are not exported are bridged via a
   "pseudo filesystem" that provides a view of exported directories
   only.  A pseudo filesystem has a unique fsid and behaves like a
   normal, read only filesystem.

   Based on the construction of the server's name space, it is possible
   that multiple pseudo filesystems may exist.  For example,

   /a         pseudo filesystem
   /a/b       real filesystem
   /a/b/c     pseudo filesystem
   /a/b/c/d   real filesystem

   Each of the pseudo filesystems are considered separate entities and
   therefore will have a unique fsid.




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7.4.  Multiple Roots

   The DOS and Windows operating environments are sometimes described as
   having "multiple roots".  Filesystems are commonly represented as
   disk letters.  MacOS represents filesystems as top level names.  NFS
   version 4 servers for these platforms can construct a pseudo file
   system above these root names so that disk letters or volume names
   are simply directory names in the pseudo root.

7.5.  Filehandle Volatility

   The nature of the server's pseudo filesystem is that it is a logical
   representation of filesystem(s) available from the server.
   Therefore, the pseudo filesystem is most likely constructed
   dynamically when the server is first instantiated.  It is expected
   that the pseudo filesystem may not have an on disk counterpart from
   which persistent filehandles could be constructed.  Even though it is
   preferable that the server provide persistent filehandles for the
   pseudo filesystem, the NFS client should expect that pseudo file
   system filehandles are volatile.  This can be confirmed by checking
   the associated "fh_expire_type" attribute for those filehandles in
   question.  If the filehandles are volatile, the NFS client must be
   prepared to recover a filehandle value (e.g., with a multi-component
   LOOKUP) when receiving an error of NFS4ERR_FHEXPIRED.

7.6.  Exported Root

   If the server's root filesystem is exported, one might conclude that
   a pseudo-filesystem is not needed.  This would be wrong.  Assume the
   following filesystems on a server:

         /       disk1  (exported)
         /a      disk2  (not exported)
         /a/b    disk3  (exported)

   Because disk2 is not exported, disk3 cannot be reached with simple
   LOOKUPs.  The server must bridge the gap with a pseudo-filesystem.

7.7.  Mount Point Crossing

   The server filesystem environment may be constructed in such a way
   that one filesystem contains a directory which is 'covered' or
   mounted upon by a second filesystem.  For example:

         /a/b            (filesystem 1)
         /a/b/c/d        (filesystem 2)





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   The pseudo filesystem for this server may be constructed to look
   like:

         /               (place holder/not exported)
         /a/b            (filesystem 1)
         /a/b/c/d        (filesystem 2)

   It is the server's responsibility to present the pseudo filesystem
   that is complete to the client.  If the client sends a lookup request
   for the path "/a/b/c/d", the server's response is the filehandle of
   the filesystem "/a/b/c/d".  In previous versions of the NFS protocol,
   the server would respond with the filehandle of directory "/a/b/c/d"
   within the filesystem "/a/b".

   The NFS client will be able to determine if it crosses a server mount
   point by a change in the value of the "fsid" attribute.

7.8.  Security Policy and Name Space Presentation

   The application of the server's security policy needs to be carefully
   considered by the implementor.  One may choose to limit the
   viewability of portions of the pseudo filesystem based on the
   server's perception of the client's ability to authenticate itself
   properly.  However, with the support of multiple security mechanisms
   and the ability to negotiate the appropriate use of these mechanisms,
   the server is unable to properly determine if a client will be able
   to authenticate itself.  If, based on its policies, the server
   chooses to limit the contents of the pseudo filesystem, the server
   may effectively hide filesystems from a client that may otherwise
   have legitimate access.

   As suggested practice, the server should apply the security policy of
   a shared resource in the server's namespace to the components of the
   resource's ancestors.  For example:

         /
         /a/b
         /a/b/c

   The /a/b/c directory is a real filesystem and is the shared resource.
   The security policy for /a/b/c is Kerberos with integrity.  The
   server should apply the same security policy to /, /a, and /a/b.
   This allows for the extension of the protection of the server's
   namespace to the ancestors of the real shared resource.







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   For the case of the use of multiple, disjoint security mechanisms in
   the server's resources, the security for a particular object in the
   server's namespace should be the union of all security mechanisms of
   all direct descendants.

8.  File Locking and Share Reservations

   Integrating locking into the NFS protocol necessarily causes it to be
   stateful.  With the inclusion of share reservations the protocol
   becomes substantially more dependent on state than the traditional
   combination of NFS and NLM [XNFS].  There are three components to
   making this state manageable:

   o  Clear division between client and server

   o  Ability to reliably detect inconsistency in state between client
      and server

   o  Simple and robust recovery mechanisms

   In this model, the server owns the state information.  The client
   communicates its view of this state to the server as needed.  The
   client is also able to detect inconsistent state before modifying a
   file.

   To support Win32 share reservations it is necessary to atomically
   OPEN or CREATE files.  Having a separate share/unshare operation
   would not allow correct implementation of the Win32 OpenFile API.  In
   order to correctly implement share semantics, the previous NFS
   protocol mechanisms used when a file is opened or created (LOOKUP,
   CREATE, ACCESS) need to be replaced.  The NFS version 4 protocol has
   an OPEN operation that subsumes the NFS version 3 methodology of
   LOOKUP, CREATE, and ACCESS.  However, because many operations require
   a filehandle, the traditional LOOKUP is preserved to map a file name
   to filehandle without establishing state on the server.  The policy
   of granting access or modifying files is managed by the server based
   on the client's state.  These mechanisms can implement policy ranging
   from advisory only locking to full mandatory locking.

8.1.  Locking

   It is assumed that manipulating a lock is rare when compared to READ
   and WRITE operations.  It is also assumed that crashes and network
   partitions are relatively rare.  Therefore it is important that the
   READ and WRITE operations have a lightweight mechanism to indicate if
   they possess a held lock.  A lock request contains the heavyweight
   information required to establish a lock and uniquely define the lock
   owner.



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   The following sections describe the transition from the heavy weight
   information to the eventual stateid used for most client and server
   locking and lease interactions.

8.1.1.  Client ID

   For each LOCK request, the client must identify itself to the server.

   This is done in such a way as to allow for correct lock
   identification and crash recovery.  A sequence of a SETCLIENTID
   operation followed by a SETCLIENTID_CONFIRM operation is required to
   establish the identification onto the server.  Establishment of
   identification by a new incarnation of the client also has the effect
   of immediately breaking any leased state that a previous incarnation
   of the client might have had on the server, as opposed to forcing the
   new client incarnation to wait for the leases to expire.  Breaking
   the lease state amounts to the server removing all lock, share
   reservation, and, where the server is not supporting the
   CLAIM_DELEGATE_PREV claim type, all delegation state associated with
   same client with the same identity.  For discussion of delegation
   state recovery, see the section "Delegation Recovery".

   Client identification is encapsulated in the following structure:

         struct nfs_client_id4 {
                 verifier4     verifier;
                 opaque        id<NFS4_OPAQUE_LIMIT>;
         };

   The first field, verifier is a client incarnation verifier that is
   used to detect client reboots.  Only if the verifier is different
   from that which the server has previously recorded the client (as
   identified by the second field of the structure, id) does the server
   start the process of canceling the client's leased state.

   The second field, id is a variable length string that uniquely
   defines the client.

   There are several considerations for how the client generates the id
   string:

   o  The string should be unique so that multiple clients do not
      present the same string.  The consequences of two clients
      presenting the same string range from one client getting an error
      to one client having its leased state abruptly and unexpectedly
      canceled.





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   o  The string should be selected so the subsequent incarnations
      (e.g., reboots) of the same client cause the client to present the
      same string.  The implementor is cautioned against an approach
      that requires the string to be recorded in a local file because
      this precludes the use of the implementation in an environment
      where there is no local disk and all file access is from an NFS
      version 4 server.

   o  The string should be different for each server network address
      that the client accesses, rather than common to all server network
      addresses.  The reason is that it may not be possible for the
      client to tell if the same server is listening on multiple network
      addresses.  If the client issues SETCLIENTID with the same id
      string to each network address of such a server, the server will
      think it is the same client, and each successive SETCLIENTID will
      cause the server to begin the process of removing the client's
      previous leased state.

   o  The algorithm for generating the string should not assume that the
      client's network address won't change.  This includes changes
      between client incarnations and even changes while the client is
      stilling running in its current incarnation.  This means that if
      the client includes just the client's and server's network address
      in the id string, there is a real risk, after the client gives up
      the network address, that another client, using a similar
      algorithm for generating the id string, will generate a
      conflicting id string.

   Given the above considerations, an example of a well generated id
   string is one that includes:

   o  The server's network address.

   o  The client's network address.

   o  For a user level NFS version 4 client, it should contain
      additional information to distinguish the client from other user
      level clients running on the same host, such as a process id or
      other unique sequence.

   o  Additional information that tends to be unique, such as one or
      more of:

      -  The client machine's serial number (for privacy reasons, it is
         best to perform some one way function on the serial number).

      -  A MAC address.




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      -  The timestamp of when the NFS version 4 software was first
         installed on the client (though this is subject to the
         previously mentioned caution about using information that is
         stored in a file, because the file might only be accessible
         over NFS version 4).

      -  A true random number.  However since this number ought to be
         the same between client incarnations, this shares the same
         problem as that of the using the timestamp of the software
         installation.

   As a security measure, the server MUST NOT cancel a client's leased
   state if the principal established the state for a given id string is
   not the same as the principal issuing the SETCLIENTID.

   Note that SETCLIENTID and SETCLIENTID_CONFIRM has a secondary purpose
   of establishing the information the server needs to make callbacks to
   the client for purpose of supporting delegations.  It is permitted to
   change this information via SETCLIENTID and SETCLIENTID_CONFIRM
   within the same incarnation of the client without removing the
   client's leased state.

   Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has successfully
   completed, the client uses the shorthand client identifier, of type
   clientid4, instead of the longer and less compact nfs_client_id4
   structure.  This shorthand client identifier (a clientid) is assigned
   by the server and should be chosen so that it will not conflict with
   a clientid previously assigned by the server.  This applies across
   server restarts or reboots.  When a clientid is presented to a server
   and that clientid is not recognized, as would happen after a server
   reboot, the server will reject the request with the error
   NFS4ERR_STALE_CLIENTID.  When this happens, the client must obtain a
   new clientid by use of the SETCLIENTID operation and then proceed to
   any other necessary recovery for the server reboot case (See the
   section "Server Failure and Recovery").

   The client must also employ the SETCLIENTID operation when it
   receives a NFS4ERR_STALE_STATEID error using a stateid derived from
   its current clientid, since this also indicates a server reboot which
   has invalidated the existing clientid (see the next section
   "lock_owner and stateid Definition" for details).

   See the detailed descriptions of SETCLIENTID and SETCLIENTID_CONFIRM
   for a complete specification of the operations.







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8.1.2.  Server Release of Clientid

   If the server determines that the client holds no associated state
   for its clientid, the server may choose to release the clientid.  The
   server may make this choice for an inactive client so that resources
   are not consumed by those intermittently active clients.  If the
   client contacts the server after this release, the server must ensure
   the client receives the appropriate error so that it will use the
   SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish a new identity.
   It should be clear that the server must be very hesitant to release a
   clientid since the resulting work on the client to recover from such
   an event will be the same burden as if the server had failed and
   restarted.  Typically a server would not release a clientid unless
   there had been no activity from that client for many minutes.

   Note that if the id string in a SETCLIENTID request is properly
   constructed, and if the client takes care to use the same principal
   for each successive use of SETCLIENTID, then, barring an active
   denial of service attack, NFS4ERR_CLID_INUSE should never be
   returned.

   However, client bugs, server bugs, or perhaps a deliberate change of
   the principal owner of the id string (such as the case of a client
   that changes security flavors, and under the new flavor, there is no
   mapping to the previous owner) will in rare cases result in
   NFS4ERR_CLID_INUSE.

   In that event, when the server gets a SETCLIENTID for a client id
   that currently has no state, or it has state, but the lease has
   expired, rather than returning NFS4ERR_CLID_INUSE, the server MUST
   allow the SETCLIENTID, and confirm the new clientid if followed by
   the appropriate SETCLIENTID_CONFIRM.

8.1.3.  lock_owner and stateid Definition

   When requesting a lock, the client must present to the server the
   clientid and an identifier for the owner of the requested lock.
   These two fields are referred to as the lock_owner and the definition
   of those fields are:

   o  A clientid returned by the server as part of the client's use of
      the SETCLIENTID operation.

   o  A variable length opaque array used to uniquely define the owner
      of a lock managed by the client.

      This may be a thread id, process id, or other unique value.




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   When the server grants the lock, it responds with a unique stateid.
   The stateid is used as a shorthand reference to the lock_owner, since
   the server will be maintaining the correspondence between them.

   The server is free to form the stateid in any manner that it chooses
   as long as it is able to recognize invalid and out-of-date stateids.
   This requirement includes those stateids generated by earlier
   instances of the server.  From this, the client can be properly
   notified of a server restart.  This notification will occur when the
   client presents a stateid to the server from a previous
   instantiation.

   The server must be able to distinguish the following situations and
   return the error as specified:

   o  The stateid was generated by an earlier server instance (i.e.,
      before a server reboot).  The error NFS4ERR_STALE_STATEID should
      be returned.

   o  The stateid was generated by the current server instance but the
      stateid no longer designates the current locking state for the
      lockowner-file pair in question (i.e., one or more locking
      operations has occurred).  The error NFS4ERR_OLD_STATEID should be
      returned.

      This error condition will only occur when the client issues a
      locking request which changes a stateid while an I/O request that
      uses that stateid is outstanding.

   o  The stateid was generated by the current server instance but the
      stateid does not designate a locking state for any active
      lockowner-file pair.  The error NFS4ERR_BAD_STATEID should be
      returned.

      This error condition will occur when there has been a logic error
      on the part of the client or server.  This should not happen.

   One mechanism that may be used to satisfy these requirements is for
   the server to,

   o  divide the "other" field of each stateid into two fields:

      -  A server verifier which uniquely designates a particular server
         instantiation.

      -  An index into a table of locking-state structures.





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   o  utilize the "seqid" field of each stateid, such that seqid is
      monotonically incremented for each stateid that is associated with
      the same index into the locking-state table.

   By matching the incoming stateid and its field values with the state
   held at the server, the server is able to easily determine if a
   stateid is valid for its current instantiation and state.  If the
   stateid is not valid, the appropriate error can be supplied to the
   client.

8.1.4.  Use of the stateid and Locking

   All READ, WRITE and SETATTR operations contain a stateid.  For the
   purposes of this section, SETATTR operations which change the size
   attribute of a file are treated as if they are writing the area
   between the old and new size (i.e., the range truncated or added to
   the file by means of the SETATTR), even where SETATTR is not
   explicitly mentioned in the text.

   If the lock_owner performs a READ or WRITE in a situation in which it
   has established a lock or share reservation on the server (any OPEN
   constitutes a share reservation) the stateid (previously returned by
   the server) must be used to indicate what locks, including both
   record locks and share reservations, are held by the lockowner.  If
   no state is established by the client, either record lock or share
   reservation, a stateid of all bits 0 is used.  Regardless whether a
   stateid of all bits 0, or a stateid returned by the server is used,
   if there is a conflicting share reservation or mandatory record lock
   held on the file, the server MUST refuse to service the READ or WRITE
   operation.

   Share reservations are established by OPEN operations and by their
   nature are mandatory in that when the OPEN denies READ or WRITE
   operations, that denial results in such operations being rejected
   with error NFS4ERR_LOCKED.  Record locks may be implemented by the
   server as either mandatory or advisory, or the choice of mandatory or
   advisory behavior may be determined by the server on the basis of the
   file being accessed (for example, some UNIX-based servers support a
   "mandatory lock bit" on the mode attribute such that if set, record
   locks are required on the file before I/O is possible).  When record
   locks are advisory, they only prevent the granting of conflicting
   lock requests and have no effect on READs or WRITEs.  Mandatory
   record locks, however, prevent conflicting I/O operations.  When they
   are attempted, they are rejected with NFS4ERR_LOCKED.  When the
   client gets NFS4ERR_LOCKED on a file it knows it has the proper share
   reservation for, it will need to issue a LOCK request on the region





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   of the file that includes the region the I/O was to be performed on,
   with an appropriate locktype (i.e., READ*_LT for a READ operation,
   WRITE*_LT for a WRITE operation).

   With NFS version 3, there was no notion of a stateid so there was no
   way to tell if the application process of the client sending the READ
   or WRITE operation had also acquired the appropriate record lock on
   the file.  Thus there was no way to implement mandatory locking.
   With the stateid construct, this barrier has been removed.

   Note that for UNIX environments that support mandatory file locking,
   the distinction between advisory and mandatory locking is subtle.  In
   fact, advisory and mandatory record locks are exactly the same in so
   far as the APIs and requirements on implementation.  If the mandatory
   lock attribute is set on the file, the server checks to see if the
   lockowner has an appropriate shared (read) or exclusive (write)
   record lock on the region it wishes to read or write to.  If there is
   no appropriate lock, the server checks if there is a conflicting lock
   (which can be done by attempting to acquire the conflicting lock on
   the behalf of the lockowner, and if successful, release the lock
   after the READ or WRITE is done), and if there is, the server returns
   NFS4ERR_LOCKED.

   For Windows environments, there are no advisory record locks, so the
   server always checks for record locks during I/O requests.

   Thus, the NFS version 4 LOCK operation does not need to distinguish
   between advisory and mandatory record locks.  It is the NFS version 4
   server's processing of the READ and WRITE operations that introduces
   the distinction.

   Every stateid other than the special stateid values noted in this
   section, whether returned by an OPEN-type operation (i.e., OPEN,
   OPEN_DOWNGRADE), or by a LOCK-type operation (i.e., LOCK or LOCKU),
   defines an access mode for the file (i.e., READ, WRITE, or READ-
   WRITE) as established by the original OPEN which began the stateid
   sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
   within that stateid sequence.  When a READ, WRITE, or SETATTR which
   specifies the size attribute, is done, the operation is subject to
   checking against the access mode to verify that the operation is
   appropriate given the OPEN with which the operation is associated.

   In the case of WRITE-type operations (i.e., WRITEs and SETATTRs which
   set size), the server must verify that the access mode allows writing
   and return an NFS4ERR_OPENMODE error if it does not.  In the case, of
   READ, the server may perform the corresponding check on the access
   mode, or it may choose to allow READ on opens for WRITE only, to
   accommodate clients whose write implementation may unavoidably do



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   reads (e.g., due to buffer cache constraints).  However, even if
   READs are allowed in these circumstances, the server MUST still check
   for locks that conflict with the READ (e.g., another open specify
   denial of READs).  Note that a server which does enforce the access
   mode check on READs need not explicitly check for conflicting share
   reservations since the existence of OPEN for read access guarantees
   that no conflicting share reservation can exist.

   A stateid of all bits 1 (one) MAY allow READ operations to bypass
   locking checks at the server.  However, WRITE operations with a
   stateid with bits all 1 (one) MUST NOT bypass locking checks and are
   treated exactly the same as if a stateid of all bits 0 were used.

   A lock may not be granted while a READ or WRITE operation using one
   of the special stateids is being performed and the range of the lock
   request conflicts with the range of the READ or WRITE operation.  For
   the purposes of this paragraph, a conflict occurs when a shared lock
   is requested and a WRITE operation is being performed, or an
   exclusive lock is requested and either a READ or a WRITE operation is
   being performed.  A SETATTR that sets size is treated similarly to a
   WRITE as discussed above.

8.1.5.  Sequencing of Lock Requests

   Locking is different than most NFS operations as it requires "at-
   most-one" semantics that are not provided by ONCRPC.  ONCRPC over a
   reliable transport is not sufficient because a sequence of locking
   requests may span multiple TCP connections.  In the face of
   retransmission or reordering, lock or unlock requests must have a
   well defined and consistent behavior.  To accomplish this, each lock
   request contains a sequence number that is a consecutively increasing
   integer.  Different lock_owners have different sequences.  The server
   maintains the last sequence number (L) received and the response that
   was returned.  The first request issued for any given lock_owner is
   issued with a sequence number of zero.

   Note that for requests that contain a sequence number, for each
   lock_owner, there should be no more than one outstanding request.

   If a request (r) with a previous sequence number (r < L) is received,
   it is rejected with the return of error NFS4ERR_BAD_SEQID.  Given a
   properly-functioning client, the response to (r) must have been
   received before the last request (L) was sent.  If a duplicate of
   last request (r == L) is received, the stored response is returned.
   If a request beyond the next sequence (r == L + 2) is received, it is
   rejected with the return of error NFS4ERR_BAD_SEQID.  Sequence
   history is reinitialized whenever the SETCLIENTID/SETCLIENTID_CONFIRM
   sequence changes the client verifier.



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   Since the sequence number is represented with an unsigned 32-bit
   integer, the arithmetic involved with the sequence number is mod
   2^32.  For an example of modulo arithmetic involving sequence numbers
   see [RFC793].

   It is critical the server maintain the last response sent to the
   client to provide a more reliable cache of duplicate non-idempotent
   requests than that of the traditional cache described in [Juszczak].
   The traditional duplicate request cache uses a least recently used
   algorithm for removing unneeded requests.  However, the last lock
   request and response on a given lock_owner must be cached as long as
   the lock state exists on the server.

   The client MUST monotonically increment the sequence number for the
   CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
   operations.  This is true even in the event that the previous
   operation that used the sequence number received an error.  The only
   exception to this rule is if the previous operation received one of
   the following errors: NFS4ERR_STALE_CLIENTID, NFS4ERR_STALE_STATEID,
   NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID, NFS4ERR_BADXDR,
   NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE.

8.1.6.  Recovery from Replayed Requests

   As described above, the sequence number is per lock_owner.  As long
   as the server maintains the last sequence number received and follows
   the methods described above, there are no risks of a Byzantine router
   re-sending old requests.  The server need only maintain the
   (lock_owner, sequence number) state as long as there are open files
   or closed files with locks outstanding.

   LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a sequence
   number and therefore the risk of the replay of these operations
   resulting in undesired effects is non-existent while the server
   maintains the lock_owner state.

8.1.7.  Releasing lock_owner State

   When a particular lock_owner no longer holds open or file locking
   state at the server, the server may choose to release the sequence
   number state associated with the lock_owner.  The server may make
   this choice based on lease expiration, for the reclamation of server
   memory, or other implementation specific details.  In any event, the
   server is able to do this safely only when the lock_owner no longer
   is being utilized by the client.  The server may choose to hold the
   lock_owner state in the event that retransmitted requests are
   received.  However, the period to hold this state is implementation
   specific.



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   In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
   retransmitted after the server has previously released the lock_owner
   state, the server will find that the lock_owner has no files open and
   an error will be returned to the client.  If the lock_owner does have
   a file open, the stateid will not match and again an error is
   returned to the client.

8.1.8.  Use of Open Confirmation

   In the case that an OPEN is retransmitted and the lock_owner is being
   used for the first time or the lock_owner state has been previously
   released by the server, the use of the OPEN_CONFIRM operation will
   prevent incorrect behavior.  When the server observes the use of the
   lock_owner for the first time, it will direct the client to perform
   the OPEN_CONFIRM for the corresponding OPEN.  This sequence
   establishes the use of an lock_owner and associated sequence number.
   Since the OPEN_CONFIRM sequence connects a new open_owner on the
   server with an existing open_owner on a client, the sequence number
   may have any value.  The OPEN_CONFIRM step assures the server that
   the value received is the correct one.  See the section "OPEN_CONFIRM
   - Confirm Open" for further details.

   There are a number of situations in which the requirement to confirm
   an OPEN would pose difficulties for the client and server, in that
   they would be prevented from acting in a timely fashion on
   information received, because that information would be provisional,
   subject to deletion upon non-confirmation.  Fortunately, these are
   situations in which the server can avoid the need for confirmation
   when responding to open requests.  The two constraints are:

   o  The server must not bestow a delegation for any open which would
      require confirmation.

   o  The server MUST NOT require confirmation on a reclaim-type open
      (i.e., one specifying claim type CLAIM_PREVIOUS or
      CLAIM_DELEGATE_PREV).

   These constraints are related in that reclaim-type opens are the only
   ones in which the server may be required to send a delegation.  For
   CLAIM_NULL, sending the delegation is optional while for
   CLAIM_DELEGATE_CUR, no delegation is sent.

   Delegations being sent with an open requiring confirmation are
   troublesome because recovering from non-confirmation adds undue
   complexity to the protocol while requiring confirmation on reclaim-
   type opens poses difficulties in that the inability to resolve





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   the status of the reclaim until lease expiration may make it
   difficult to have timely determination of the set of locks being
   reclaimed (since the grace period may expire).

   Requiring open confirmation on reclaim-type opens is avoidable
   because of the nature of the environments in which such opens are
   done.  For CLAIM_PREVIOUS opens, this is immediately after server
   reboot, so there should be no time for lockowners to be created,
   found to be unused, and recycled.  For CLAIM_DELEGATE_PREV opens, we
   are dealing with a client reboot situation.  A server which supports
   delegation can be sure that no lockowners for that client have been
   recycled since client initialization and thus can ensure that
   confirmation will not be required.

8.2.  Lock Ranges

   The protocol allows a lock owner to request a lock with a byte range
   and then either upgrade or unlock a sub-range of the initial lock.
   It is expected that this will be an uncommon type of request.  In any
   case, servers or server filesystems may not be able to support sub-
   range lock semantics.  In the event that a server receives a locking
   request that represents a sub-range of current locking state for the
   lock owner, the server is allowed to return the error
   NFS4ERR_LOCK_RANGE to signify that it does not support sub-range lock
   operations.  Therefore, the client should be prepared to receive this
   error and, if appropriate, report the error to the requesting
   application.

   The client is discouraged from combining multiple independent locking
   ranges that happen to be adjacent into a single request since the
   server may not support sub-range requests and for reasons related to
   the recovery of file locking state in the event of server failure.
   As discussed in the section "Server Failure and Recovery" below, the
   server may employ certain optimizations during recovery that work
   effectively only when the client's behavior during lock recovery is
   similar to the client's locking behavior prior to server failure.

8.3.  Upgrading and Downgrading Locks

   If a client has a write lock on a record, it can request an atomic
   downgrade of the lock to a read lock via the LOCK request, by setting
   the type to READ_LT.  If the server supports atomic downgrade, the
   request will succeed.  If not, it will return NFS4ERR_LOCK_NOTSUPP.
   The client should be prepared to receive this error, and if
   appropriate, report the error to the requesting application.






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   If a client has a read lock on a record, it can request an atomic
   upgrade of the lock to a write lock via the LOCK request by setting
   the type to WRITE_LT or WRITEW_LT.  If the server does not support
   atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the upgrade
   can be achieved without an existing conflict, the request will
   succeed.  Otherwise, the server will return either NFS4ERR_DENIED or
   NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the
   client issued the LOCK request with the type set to WRITEW_LT and the
   server has detected a deadlock.  The client should be prepared to
   receive such errors and if appropriate, report the error to the
   requesting application.

8.4.  Blocking Locks

   Some clients require the support of blocking locks.  The NFS version
   4 protocol must not rely on a callback mechanism and therefore is
   unable to notify a client when a previously denied lock has been
   granted.  Clients have no choice but to continually poll for the
   lock.  This presents a fairness problem.  Two new lock types are
   added, READW and WRITEW, and are used to indicate to the server that
   the client is requesting a blocking lock.  The server should maintain
   an ordered list of pending blocking locks.  When the conflicting lock
   is released, the server may wait the lease period for the first
   waiting client to re-request the lock.  After the lease period
   expires the next waiting client request is allowed the lock.  Clients
   are required to poll at an interval sufficiently small that it is
   likely to acquire the lock in a timely manner.  The server is not
   required to maintain a list of pending blocked locks as it is used to
   increase fairness and not correct operation.  Because of the
   unordered nature of crash recovery, storing of lock state to stable
   storage would be required to guarantee ordered granting of blocking
   locks.

   Servers may also note the lock types and delay returning denial of
   the request to allow extra time for a conflicting lock to be
   released, allowing a successful return.  In this way, clients can
   avoid the burden of needlessly frequent polling for blocking locks.
   The server should take care in the length of delay in the event the
   client retransmits the request.

8.5.  Lease Renewal

   The purpose of a lease is to allow a server to remove stale locks
   that are held by a client that has crashed or is otherwise
   unreachable.  It is not a mechanism for cache consistency and lease
   renewals may not be denied if the lease interval has not expired.





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   The following events cause implicit renewal of all of the leases for
   a given client (i.e., all those sharing a given clientid).  Each of
   these is a positive indication that the client is still active and
   that the associated state held at the server, for the client, is
   still valid.

   o  An OPEN with a valid clientid.

   o  Any operation made with a valid stateid (CLOSE, DELEGPURGE,
      DELEGRETURN, LOCK, LOCKU, OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE,
      READ, RENEW, SETATTR, WRITE).  This does not include the special
      stateids of all bits 0 or all bits 1.

      Note that if the client had restarted or rebooted, the client
      would not be making these requests without issuing the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence.  The use of the
      SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the
      client verifier) notifies the server to drop the locking state
      associated with the client.  SETCLIENTID/SETCLIENTID_CONFIRM never
      renews a lease.

      If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
      error) or the clientid (NFS4ERR_STALE_CLIENTID error) will not be
      valid hence preventing spurious renewals.

   This approach allows for low overhead lease renewal which scales
   well.  In the typical case no extra RPC calls are required for lease
   renewal and in the worst case one RPC is required every lease period
   (i.e., a RENEW operation).  The number of locks held by the client is
   not a factor since all state for the client is involved with the
   lease renewal action.

   Since all operations that create a new lease also renew existing
   leases, the server must maintain a common lease expiration time for
   all valid leases for a given client.  This lease time can then be
   easily updated upon implicit lease renewal actions.

8.6.  Crash Recovery

   The important requirement in crash recovery is that both the client
   and the server know when the other has failed.  Additionally, it is
   required that a client sees a consistent view of data across server
   restarts or reboots.  All READ and WRITE operations that may have
   been queued within the client or network buffers must wait until the
   client has successfully recovered the locks protecting the READ and
   WRITE operations.





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8.6.1.  Client Failure and Recovery

   In the event that a client fails, the server may recover the client's
   locks when the associated leases have expired.  Conflicting locks
   from another client may only be granted after this lease expiration.
   If the client is able to restart or reinitialize within the lease
   period the client may be forced to wait the remainder of the lease
   period before obtaining new locks.

   To minimize client delay upon restart, lock requests are associated
   with an instance of the client by a client supplied verifier.  This
   verifier is part of the initial SETCLIENTID call made by the client.
   The server returns a clientid as a result of the SETCLIENTID
   operation.  The client then confirms the use of the clientid with
   SETCLIENTID_CONFIRM.  The clientid in combination with an opaque
   owner field is then used by the client to identify the lock owner for
   OPEN.  This chain of associations is then used to identify all locks
   for a particular client.

   Since the verifier will be changed by the client upon each
   initialization, the server can compare a new verifier to the verifier
   associated with currently held locks and determine that they do not
   match.  This signifies the client's new instantiation and subsequent
   loss of locking state.  As a result, the server is free to release
   all locks held which are associated with the old clientid which was
   derived from the old verifier.

   Note that the verifier must have the same uniqueness properties of
   the verifier for the COMMIT operation.

8.6.2.  Server Failure and Recovery

   If the server loses locking state (usually as a result of a restart
   or reboot), it must allow clients time to discover this fact and re-
   establish the lost locking state.  The client must be able to re-
   establish the locking state without having the server deny valid
   requests because the server has granted conflicting access to another
   client.  Likewise, if there is the possibility that clients have not
   yet re-established their locking state for a file, the server must
   disallow READ and WRITE operations for that file.  The duration of
   this recovery period is equal to the duration of the lease period.

   A client can determine that server failure (and thus loss of locking
   state) has occurred, when it receives one of two errors.  The
   NFS4ERR_STALE_STATEID error indicates a stateid invalidated by a
   reboot or restart.  The NFS4ERR_STALE_CLIENTID error indicates a





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   clientid invalidated by reboot or restart.  When either of these are
   received, the client must establish a new clientid (See the section
   "Client ID") and re-establish the locking state as discussed below.

   The period of special handling of locking and READs and WRITEs, equal
   in duration to the lease period, is referred to as the "grace
   period".  During the grace period, clients recover locks and the
   associated state by reclaim-type locking requests (i.e., LOCK
   requests with reclaim set to true and OPEN operations with a claim
   type of CLAIM_PREVIOUS).  During the grace period, the server must
   reject READ and WRITE operations and non-reclaim locking requests
   (i.e., other LOCK and OPEN operations) with an error of
   NFS4ERR_GRACE.

   If the server can reliably determine that granting a non-reclaim
   request will not conflict with reclamation of locks by other clients,
   the NFS4ERR_GRACE error does not have to be returned and the non-
   reclaim client request can be serviced.  For the server to be able to
   service READ and WRITE operations during the grace period, it must
   again be able to guarantee that no possible conflict could arise
   between an impending reclaim locking request and the READ or WRITE
   operation.  If the server is unable to offer that guarantee, the
   NFS4ERR_GRACE error must be returned to the client.

   For a server to provide simple, valid handling during the grace
   period, the easiest method is to simply reject all non-reclaim
   locking requests and READ and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, a server may keep information about
   granted locks in stable storage.  With this information, the server
   could determine if a regular lock or READ or WRITE operation can be
   safely processed.

   For example, if a count of locks on a given file is available in
   stable storage, the server can track reclaimed locks for the file and
   when all reclaims have been processed, non-reclaim locking requests
   may be processed.  This way the server can ensure that non-reclaim
   locking requests will not conflict with potential reclaim requests.
   With respect to I/O requests, if the server is able to determine that
   there are no outstanding reclaim requests for a file by information
   from stable storage or another similar mechanism, the processing of
   I/O requests could proceed normally for the file.

   To reiterate, for a server that allows non-reclaim lock and I/O
   requests to be processed during the grace period, it MUST determine
   that no lock subsequently reclaimed will be rejected and that no lock
   subsequently reclaimed would have prevented any I/O operation
   processed during the grace period.




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   Clients should be prepared for the return of NFS4ERR_GRACE errors for
   non-reclaim lock and I/O requests.  In this case the client should
   employ a retry mechanism for the request.  A delay (on the order of
   several seconds) between retries should be used to avoid overwhelming
   the server.  Further discussion of the general issue is included in
   [Floyd].  The client must account for the server that is able to
   perform I/O and non-reclaim locking requests within the grace period
   as well as those that can not do so.

   A reclaim-type locking request outside the server's grace period can
   only succeed if the server can guarantee that no conflicting lock or
   I/O request has been granted since reboot or restart.

   A server may, upon restart, establish a new value for the lease
   period.  Therefore, clients should, once a new clientid is
   established, refetch the lease_time attribute and use it as the basis
   for lease renewal for the lease associated with that server.
   However, the server must establish, for this restart event, a grace
   period at least as long as the lease period for the previous server
   instantiation.  This allows the client state obtained during the
   previous server instance to be reliably re-established.

8.6.3.  Network Partitions and Recovery

   If the duration of a network partition is greater than the lease
   period provided by the server, the server will have not received a
   lease renewal from the client.  If this occurs, the server may free
   all locks held for the client.  As a result, all stateids held by the
   client will become invalid or stale.  Once the client is able to
   reach the server after such a network partition, all I/O submitted by
   the client with the now invalid stateids will fail with the server
   returning the error NFS4ERR_EXPIRED.  Once this error is received,
   the client will suitably notify the application that held the lock.

   As a courtesy to the client or as an optimization, the server may
   continue to hold locks on behalf of a client for which recent
   communication has extended beyond the lease period.  If the server
   receives a lock or I/O request that conflicts with one of these
   courtesy locks, the server must free the courtesy lock and grant the
   new request.

   When a network partition is combined with a server reboot, there are
   edge conditions that place requirements on the server in order to
   avoid silent data corruption following the server reboot.  Two of
   these edge conditions are known, and are discussed below.






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   The first edge condition has the following scenario:

      1. Client A acquires a lock.

      2. Client A and server experience mutual network partition, such
         that client A is unable to renew its lease.

      3. Client A's lease expires, so server releases lock.

      4. Client B acquires a lock that would have conflicted with that
         of Client A.

      5. Client B releases the lock

      6. Server reboots

      7. Network partition between client A and server heals.

      8. Client A issues a RENEW operation, and gets back a
         NFS4ERR_STALE_CLIENTID.

      9. Client A reclaims its lock within the server's grace period.

   Thus, at the final step, the server has erroneously granted client
   A's lock reclaim.  If client B modified the object the lock was
   protecting, client A will experience object corruption.

   The second known edge condition follows:

      1. Client A acquires a lock.

      2. Server reboots.

      3. Client A and server experience mutual network partition, such
         that client A is unable to reclaim its lock within the grace
         period.

      4. Server's reclaim grace period ends.  Client A has no locks
         recorded on server.

      5. Client B acquires a lock that would have conflicted with that
         of Client A.

      6. Client B releases the lock.

      7. Server reboots a second time.

      8. Network partition between client A and server heals.



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      9. Client A issues a RENEW operation, and gets back a
         NFS4ERR_STALE_CLIENTID.

     10. Client A reclaims its lock within the server's grace period.

   As with the first edge condition, the final step of the scenario of
   the second edge condition has the server erroneously granting client
   A's lock reclaim.

   Solving the first and second edge conditions requires that the server
   either assume after it reboots that edge condition occurs, and thus
   return NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
   record some information stable storage.  The amount of information
   the server records in stable storage is in inverse proportion to how
   harsh the server wants to be whenever the edge conditions occur.  The
   server that is completely tolerant of all edge conditions will record
   in stable storage every lock that is acquired, removing the lock
   record from stable storage only when the lock is unlocked by the
   client and the lock's lockowner advances the sequence number such
   that the lock release is not the last stateful event for the
   lockowner's sequence.  For the two aforementioned edge conditions,
   the harshest a server can be, and still support a grace period for
   reclaims, requires that the server record in stable storage
   information some minimal information.  For example, a server
   implementation could, for each client, save in stable storage a
   record containing:

   o  the client's id string

   o  a boolean that indicates if the client's lease expired or if there
      was administrative intervention (see the section, Server
      Revocation of Locks) to revoke a record lock, share reservation,
      or delegation

   o  a timestamp that is updated the first time after a server boot or
      reboot the client acquires record locking, share reservation, or
      delegation state on the server.  The timestamp need not be updated
      on subsequent lock requests until the server reboots.

   The server implementation would also record in the stable storage the
   timestamps from the two most recent server reboots.

   Assuming the above record keeping, for the first edge condition,
   after the server reboots, the record that client A's lease expired
   means that another client could have acquired a conflicting record
   lock, share reservation, or delegation.  Hence the server must reject
   a reclaim from client A with the error NFS4ERR_NO_GRACE.




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   For the second edge condition, after the server reboots for a second
   time, the record that the client had an unexpired record lock, share
   reservation, or delegation established before the server's previous
   incarnation means that the server must reject a reclaim from client A
   with the error NFS4ERR_NO_GRACE.

   Regardless of the level and approach to record keeping, the server
   MUST implement one of the following strategies (which apply to
   reclaims of share reservations, record locks, and delegations):

      1. Reject all reclaims with NFS4ERR_NO_GRACE.  This is superharsh,
         but necessary if the server does not want to record lock state
         in stable storage.

      2. Record sufficient state in stable storage such that all known
         edge conditions involving server reboot, including the two
         noted in this section, are detected.  False positives are
         acceptable.  Note that at this time, it is not known if there
         are other edge conditions.

         In the event, after a server reboot, the server determines that
         there is unrecoverable damage or corruption to the the stable
         storage, then for all clients and/or locks affected, the server
         MUST return NFS4ERR_NO_GRACE.

   A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
   outside the scope of this specification, since the strategies for
   such handling are very dependent on the client's operating
   environment.  However, one potential approach is described below.

   When the client receives NFS4ERR_NO_GRACE, it could examine the
   change attribute of the objects the client is trying to reclaim state
   for, and use that to determine whether to re-establish the state via
   normal OPEN or LOCK requests.  This is acceptable provided the
   client's operating environment allows it.  In otherwords, the client
   implementor is advised to document for his users the behavior.  The
   client could also inform the application that its record lock or
   share reservations (whether they were delegated or not) have been
   lost, such as via a UNIX signal, a GUI pop-up window, etc.  See the
   section, "Data Caching and Revocation" for a discussion of what the
   client should do for dealing with unreclaimed delegations on client
   state.

   For further discussion of revocation of locks see the section "Server
   Revocation of Locks".






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8.7.  Recovery from a Lock Request Timeout or Abort

   In the event a lock request times out, a client may decide to not
   retry the request.  The client may also abort the request when the
   process for which it was issued is terminated (e.g., in UNIX due to a
   signal).  It is possible though that the server received the request
   and acted upon it.  This would change the state on the server without
   the client being aware of the change.  It is paramount that the
   client re-synchronize state with server before it attempts any other
   operation that takes a seqid and/or a stateid with the same
   lock_owner.  This is straightforward to do without a special re-
   synchronize operation.

   Since the server maintains the last lock request and response
   received on the lock_owner, for each lock_owner, the client should
   cache the last lock request it sent such that the lock request did
   not receive a response.  From this, the next time the client does a
   lock operation for the lock_owner, it can send the cached request, if
   there is one, and if the request was one that established state
   (e.g., a LOCK or OPEN operation), the server will return the cached
   result or if never saw the request, perform it.  The client can
   follow up with a request to remove the state (e.g., a LOCKU or CLOSE
   operation).  With this approach, the sequencing and stateid
   information on the client and server for the given lock_owner will
   re-synchronize and in turn the lock state will re-synchronize.

8.8.  Server Revocation of Locks

   At any point, the server can revoke locks held by a client and the
   client must be prepared for this event.  When the client detects that
   its locks have been or may have been revoked, the client is
   responsible for validating the state information between itself and
   the server.  Validating locking state for the client means that it
   must verify or reclaim state for each lock currently held.

   The first instance of lock revocation is upon server reboot or re-
   initialization.  In this instance the client will receive an error
   (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the client will
   proceed with normal crash recovery as described in the previous
   section.

   The second lock revocation event is the inability to renew the lease
   before expiration.  While this is considered a rare or unusual event,
   the client must be prepared to recover.  Both the server and client
   will be able to detect the failure to renew the lease and are capable
   of recovering without data corruption.  For the server, it tracks the
   last renewal event serviced for the client and knows when the lease
   will expire.  Similarly, the client must track operations which will



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   renew the lease period.  Using the time that each such request was
   sent and the time that the corresponding reply was received, the
   client should bound the time that the corresponding renewal could
   have occurred on the server and thus determine if it is possible that
   a lease period expiration could have occurred.

   The third lock revocation event can occur as a result of
   administrative intervention within the lease period.  While this is
   considered a rare event, it is possible that the server's
   administrator has decided to release or revoke a particular lock held
   by the client.  As a result of revocation, the client will receive an
   error of NFS4ERR_ADMIN_REVOKED.  In this instance the client may
   assume that only the lock_owner's locks have been lost.  The client
   notifies the lock holder appropriately.  The client may not assume
   the lease period has been renewed as a result of failed operation.

   When the client determines the lease period may have expired, the
   client must mark all locks held for the associated lease as
   "unvalidated".  This means the client has been unable to re-establish
   or confirm the appropriate lock state with the server.  As described
   in the previous section on crash recovery, there are scenarios in
   which the server may grant conflicting locks after the lease period
   has expired for a client.  When it is possible that the lease period
   has expired, the client must validate each lock currently held to
   ensure that a conflicting lock has not been granted.  The client may
   accomplish this task by issuing an I/O request, either a pending I/O
   or a zero-length read, specifying the stateid associated with the
   lock in question.  If the response to the request is success, the
   client has validated all of the locks governed by that stateid and
   re-established the appropriate state between itself and the server.

   If the I/O request is not successful, then one or more of the locks
   associated with the stateid was revoked by the server and the client
   must notify the owner.

8.9.  Share Reservations

   A share reservation is a mechanism to control access to a file.  It
   is a separate and independent mechanism from record locking.  When a
   client opens a file, it issues an OPEN operation to the server
   specifying the type of access required (READ, WRITE, or BOTH) and the
   type of access to deny others (deny NONE, READ, WRITE, or BOTH).  If
   the OPEN fails the client will fail the application's open request.

   Pseudo-code definition of the semantics:

   if (request.access == 0)
      return (NFS4ERR_INVAL)



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   else
      if ((request.access & file_state.deny)) ||
            (request.deny & file_state.access))
                    return (NFS4ERR_DENIED)

   This checking of share reservations on OPEN is done with no exception
   for an existing OPEN for the same open_owner.

   The constants used for the OPEN and OPEN_DOWNGRADE operations for the
   access and deny fields are as follows:

   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

8.10.  OPEN/CLOSE Operations

   To provide correct share semantics, a client MUST use the OPEN
   operation to obtain the initial filehandle and indicate the desired
   access and what if any access to deny.  Even if the client intends to
   use a stateid of all 0's or all 1's, it must still obtain the
   filehandle for the regular file with the OPEN operation so the
   appropriate share semantics can be applied.  For clients that do not
   have a deny mode built into their open programming interfaces, deny
   equal to NONE should be used.

   The OPEN operation with the CREATE flag, also subsumes the CREATE
   operation for regular files as used in previous versions of the NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the
   lock_owner on that file.  If record locks are held, the client SHOULD
   release all locks before issuing a CLOSE.  The server MAY free all
   outstanding locks on CLOSE but some servers may not support the CLOSE
   of a file that still has record locks held.  The server MUST return
   failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
   CLOSE.

   The LOOKUP operation will return a filehandle without establishing
   any lock state on the server.  Without a valid stateid, the server
   will assume the client has the least access.  For example, a file





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   opened with deny READ/WRITE cannot be accessed using a filehandle
   obtained through LOOKUP because it would not have a valid stateid
   (i.e., using a stateid of all bits 0 or all bits 1).

8.10.1.  Close and Retention of State Information

   Since a CLOSE operation requests deallocation of a stateid, dealing
   with retransmission of the CLOSE, may pose special difficulties,
   since the state information, which normally would be used to
   determine the state of the open file being designated, might be
   deallocated, resulting in an NFS4ERR_BAD_STATEID error.

   Servers may deal with this problem in a number of ways.  To provide
   the greatest degree assurance that the protocol is being used
   properly, a server should, rather than deallocate the stateid, mark
   it as close-pending, and retain the stateid with this status, until
   later deallocation.  In this way, a retransmitted CLOSE can be
   recognized since the stateid points to state information with this
   distinctive status, so that it can be handled without error.

   When adopting this strategy, a server should retain the state
   information until the earliest of:

   o  Another validly sequenced request for the same lockowner, that is
      not a retransmission.

   o  The time that a lockowner is freed by the server due to period
      with no activity.

   o  All locks for the client are freed as a result of a SETCLIENTID.

   Servers may avoid this complexity, at the cost of less complete
   protocol error checking, by simply responding NFS4_OK in the event of
   a CLOSE for a deallocated stateid, on the assumption that this case
   must be caused by a retransmitted close.  When adopting this
   approach, it is desirable to at least log an error when returning a
   no-error indication in this situation.  If the server maintains a
   reply-cache mechanism, it can verify the CLOSE is indeed a
   retransmission and avoid error logging in most cases.

8.11.  Open Upgrade and Downgrade

   When an OPEN is done for a file and the lockowner for which the open
   is being done already has the file open, the result is to upgrade the
   open file status maintained on the server to include the access and
   deny bits specified by the new OPEN as well as those for the existing
   OPEN.  The result is that there is one open file, as far as the
   protocol is concerned, and it includes the union of the access and



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   deny bits for all of the OPEN requests completed.  Only a single
   CLOSE will be done to reset the effects of both OPENs.  Note that the
   client, when issuing the OPEN, may not know that the same file is in
   fact being opened.  The above only applies if both OPENs result in
   the OPENed object being designated by the same filehandle.

   When the server chooses to export multiple filehandles corresponding
   to the same file object and returns different filehandles on two
   different OPENs of the same file object, the server MUST NOT "OR"
   together the access and deny bits and coalesce the two open files.
   Instead the server must maintain separate OPENs with separate
   stateids and will require separate CLOSEs to free them.

   When multiple open files on the client are merged into a single open
   file object on the server, the close of one of the open files (on the
   client) may necessitate change of the access and deny status of the
   open file on the server.  This is because the union of the access and
   deny bits for the remaining opens may be smaller (i.e., a proper
   subset) than previously.  The OPEN_DOWNGRADE operation is used to
   make the necessary change and the client should use it to update the
   server so that share reservation requests by other clients are
   handled properly.

8.12.  Short and Long Leases

   When determining the time period for the server lease, the usual
   lease tradeoffs apply.  Short leases are good for fast server
   recovery at a cost of increased RENEW or READ (with zero length)
   requests.  Longer leases are certainly kinder and gentler to servers
   trying to handle very large numbers of clients.  The number of RENEW
   requests drop in proportion to the lease time.  The disadvantages of
   long leases are slower recovery after server failure (the server must
   wait for the leases to expire and the grace period to elapse before
   granting new lock requests) and increased file contention (if client
   fails to transmit an unlock request then server must wait for lease
   expiration before granting new locks).

   Long leases are usable if the server is able to store lease state in
   non-volatile memory.  Upon recovery, the server can reconstruct the
   lease state from its non-volatile memory and continue operation with
   its clients and therefore long leases would not be an issue.

8.13.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the need for synchronized clocks, lease times are granted by
   the server as a time delta.  However, there is a requirement that the
   client and server clocks do not drift excessively over the duration
   of the lock.  There is also the issue of propagation delay across the



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   network which could easily be several hundred milliseconds as well as
   the possibility that requests will be lost and need to be
   retransmitted.

   To take propagation delay into account, the client should subtract it
   from lease times (e.g., if the client estimates the one-way
   propagation delay as 200 msec, then it can assume that the lease is
   already 200 msec old when it gets it).  In addition, it will take
   another 200 msec to get a response back to the server.  So the client
   must send a lock renewal or write data back to the server 400 msec
   before the lease would expire.

   The server's lease period configuration should take into account the
   network distance of the clients that will be accessing the server's
   resources.  It is expected that the lease period will take into
   account the network propagation delays and other network delay
   factors for the client population.  Since the protocol does not allow
   for an automatic method to determine an appropriate lease period, the
   server's administrator may have to tune the lease period.

8.14.  Migration, Replication and State

   When responsibility for handling a given file system is transferred
   to a new server (migration) or the client chooses to use an alternate
   server (e.g., in response to server unresponsiveness) in the context
   of file system replication, the appropriate handling of state shared
   between the client and server (i.e., locks, leases, stateids, and
   clientids) is as described below.  The handling differs between
   migration and replication.  For related discussion of file server
   state and recover of such see the sections under "File Locking and
   Share Reservations".

   If server replica or a server immigrating a filesystem agrees to, or
   is expected to, accept opaque values from the client that originated
   from another server, then it is a wise implementation practice for
   the servers to encode the "opaque" values in network byte order.
   This way, servers acting as replicas or immigrating filesystems will
   be able to parse values like stateids, directory cookies,
   filehandles, etc. even if their native byte order is different from
   other servers cooperating in the replication and migration of the
   filesystem.

8.14.1.  Migration and State

   In the case of migration, the servers involved in the migration of a
   filesystem SHOULD transfer all server state from the original to the
   new server.  This must be done in a way that is transparent to the
   client.  This state transfer will ease the client's transition when a



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   filesystem migration occurs.  If the servers are successful in
   transferring all state, the client will continue to use stateids
   assigned by the original server.  Therefore the new server must
   recognize these stateids as valid.  This holds true for the clientid
   as well.  Since responsibility for an entire filesystem is
   transferred with a migration event, there is no possibility that
   conflicts will arise on the new server as a result of the transfer of
   locks.

   As part of the transfer of information between servers, leases would
   be transferred as well.  The leases being transferred to the new
   server will typically have a different expiration time from those for
   the same client, previously on the old server.  To maintain the
   property that all leases on a given server for a given client expire
   at the same time, the server should advance the expiration time to
   the later of the leases being transferred or the leases already
   present.  This allows the client to maintain lease renewal of both
   classes without special effort.

   The servers may choose not to transfer the state information upon
   migration.  However, this choice is discouraged.  In this case, when
   the client presents state information from the original server, the
   client must be prepared to receive either NFS4ERR_STALE_CLIENTID or
   NFS4ERR_STALE_STATEID from the new server.  The client should then
   recover its state information as it normally would in response to a
   server failure.  The new server must take care to allow for the
   recovery of state information as it would in the event of server
   restart.

8.14.2.  Replication and State

   Since client switch-over in the case of replication is not under
   server control, the handling of state is different.  In this case,
   leases, stateids and clientids do not have validity across a
   transition from one server to another.  The client must re-establish
   its locks on the new server.  This can be compared to the re-
   establishment of locks by means of reclaim-type requests after a
   server reboot.  The difference is that the server has no provision to
   distinguish requests reclaiming locks from those obtaining new locks
   or to defer the latter.  Thus, a client re-establishing a lock on the
   new server (by means of a LOCK or OPEN request), may have the
   requests denied due to a conflicting lock.  Since replication is
   intended for read-only use of filesystems, such denial of locks
   should not pose large difficulties in practice.  When an attempt to
   re-establish a lock on a new server is denied, the client should
   treat the situation as if his original lock had been revoked.





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8.14.3.  Notification of Migrated Lease

   In the case of lease renewal, the client may not be submitting
   requests for a filesystem that has been migrated to another server.
   This can occur because of the implicit lease renewal mechanism.  The
   client renews leases for all filesystems when submitting a request to
   any one filesystem at the server.

   In order for the client to schedule renewal of leases that may have
   been relocated to the new server, the client must find out about
   lease relocation before those leases expire.  To accomplish this, all
   operations which implicitly renew leases for a client (i.e., OPEN,
   CLOSE, READ, WRITE, RENEW, LOCK, LOCKT, LOCKU), will return the error
   NFS4ERR_LEASE_MOVED if responsibility for any of the leases to be
   renewed has been transferred to a new server.  This condition will
   continue until the client receives an NFS4ERR_MOVED error and the
   server receives the subsequent GETATTR(fs_locations) for an access to
   each filesystem for which a lease has been moved to a new server.

   When a client receives an NFS4ERR_LEASE_MOVED error, it should
   perform an operation on each filesystem associated with the server in
   question.  When the client receives an NFS4ERR_MOVED error, the
   client can follow the normal process to obtain the new server
   information (through the fs_locations attribute) and perform renewal
   of those leases on the new server.  If the server has not had state
   transferred to it transparently, the client will receive either
   NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new server,
   as described above, and the client can then recover state information
   as it does in the event of server failure.

8.14.4.  Migration and the Lease_time Attribute

   In order that the client may appropriately manage its leases in the
   case of migration, the destination server must establish proper
   values for the lease_time attribute.

   When state is transferred transparently, that state should include
   the correct value of the lease_time attribute.  The lease_time
   attribute on the destination server must never be less than that on
   the source since this would result in premature expiration of leases
   granted by the source server.  Upon migration in which state is
   transferred transparently, the client is under no obligation to re-
   fetch the lease_time attribute and may continue to use the value
   previously fetched (on the source server).

   If state has not been transferred transparently (i.e., the client
   sees a real or simulated server reboot), the client should fetch the
   value of lease_time on the new (i.e., destination) server, and use it



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   for subsequent locking requests.  However the server must respect a
   grace period at least as long as the lease_time on the source server,
   in order to ensure that clients have ample time to reclaim their
   locks before potentially conflicting non-reclaimed locks are granted.
   The means by which the new server obtains the value of lease_time on
   the old server is left to the server implementations.  It is not
   specified by the NFS version 4 protocol.

9.  Client-Side Caching

   Client-side caching of data, of file attributes, and of file names is
   essential to providing good performance with the NFS protocol.
   Providing distributed cache coherence is a difficult problem and
   previous versions of the NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been used
   to reduce the problems that a lack of coherence poses for users.
   These techniques have not been clearly defined by earlier protocol
   specifications and it is often unclear what is valid or invalid
   client behavior.

   The NFS version 4 protocol uses many techniques similar to those that
   have been used in previous protocol versions.  The NFS version 4
   protocol does not provide distributed cache coherence.  However, it
   defines a more limited set of caching guarantees to allow locks and
   share reservations to be used without destructive interference from
   client side caching.

   In addition, the NFS version 4 protocol introduces a delegation
   mechanism which allows many decisions normally made by the server to
   be made locally by clients.  This mechanism provides efficient
   support of the common cases where sharing is infrequent or where
   sharing is read-only.

9.1.  Performance Challenges for Client-Side Caching

   Caching techniques used in previous versions of the NFS protocol have
   been successful in providing good performance.  However, several
   scalability challenges can arise when those techniques are used with
   very large numbers of clients.  This is particularly true when
   clients are geographically distributed which classically increases
   the latency for cache revalidation requests.

   The previous versions of the NFS protocol repeat their file data
   cache validation requests at the time the file is opened.  This
   behavior can have serious performance drawbacks.  A common case is
   one in which a file is only accessed by a single client.  Therefore,
   sharing is infrequent.




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   In this case, repeated reference to the server to find that no
   conflicts exist is expensive.  A better option with regards to
   performance is to allow a client that repeatedly opens a file to do
   so without reference to the server.  This is done until potentially
   conflicting operations from another client actually occur.

   A similar situation arises in connection with file locking.  Sending
   file lock and unlock requests to the server as well as the read and
   write requests necessary to make data caching consistent with the
   locking semantics (see the section "Data Caching and File Locking")
   can severely limit performance.  When locking is used to provide
   protection against infrequent conflicts, a large penalty is incurred.
   This penalty may discourage the use of file locking by applications.

   The NFS version 4 protocol provides more aggressive caching
   strategies with the following design goals:

   o  Compatibility with a large range of server semantics.

   o  Provide the same caching benefits as previous versions of the NFS
      protocol when unable to provide the more aggressive model.

   o  Requirements for aggressive caching are organized so that a large
      portion of the benefit can be obtained even when not all of the
      requirements can be met.

   The appropriate requirements for the server are discussed in later
   sections in which specific forms of caching are covered.  (see the
   section "Open Delegation").

9.2.  Delegation and Callbacks

   Recallable delegation of server responsibilities for a file to a
   client improves performance by avoiding repeated requests to the
   server in the absence of inter-client conflict.  With the use of a
   "callback" RPC from server to client, a server recalls delegated
   responsibilities when another client engages in sharing of a
   delegated file.

   A delegation is passed from the server to the client, specifying the
   object of the delegation and the type of delegation.  There are
   different types of delegations but each type contains a stateid to be
   used to represent the delegation when performing operations that
   depend on the delegation.  This stateid is similar to those
   associated with locks and share reservations but differs in that the
   stateid for a delegation is associated with a clientid and may be





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   used on behalf of all the open_owners for the given client.  A
   delegation is made to the client as a whole and not to any specific
   process or thread of control within it.

   Because callback RPCs may not work in all environments (due to
   firewalls, for example), correct protocol operation does not depend
   on them.  Preliminary testing of callback functionality by means of a
   CB_NULL procedure determines whether callbacks can be supported.  The
   CB_NULL procedure checks the continuity of the callback path.  A
   server makes a preliminary assessment of callback availability to a
   given client and avoids delegating responsibilities until it has
   determined that callbacks are supported.  Because the granting of a
   delegation is always conditional upon the absence of conflicting
   access, clients must not assume that a delegation will be granted and
   they must always be prepared for OPENs to be processed without any
   delegations being granted.

   Once granted, a delegation behaves in most ways like a lock.  There
   is an associated lease that is subject to renewal together with all
   of the other leases held by that client.

   Unlike locks, an operation by a second client to a delegated file
   will cause the server to recall a delegation through a callback.

   On recall, the client holding the delegation must flush modified
   state (such as modified data) to the server and return the
   delegation.  The conflicting request will not receive a response
   until the recall is complete.  The recall is considered complete when
   the client returns the delegation or the server times out on the
   recall and revokes the delegation as a result of the timeout.
   Following the resolution of the recall, the server has the
   information necessary to grant or deny the second client's request.

   At the time the client receives a delegation recall, it may have
   substantial state that needs to be flushed to the server.  Therefore,
   the server should allow sufficient time for the delegation to be
   returned since it may involve numerous RPCs to the server.  If the
   server is able to determine that the client is diligently flushing
   state to the server as a result of the recall, the server may extend
   the usual time allowed for a recall.  However, the time allowed for
   recall completion should not be unbounded.

   An example of this is when responsibility to mediate opens on a given
   file is delegated to a client (see the section "Open Delegation").
   The server will not know what opens are in effect on the client.
   Without this knowledge the server will be unable to determine if the
   access and deny state for the file allows any particular open until
   the delegation for the file has been returned.



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   A client failure or a network partition can result in failure to
   respond to a recall callback.  In this case, the server will revoke
   the delegation which in turn will render useless any modified state
   still on the client.

9.2.1.  Delegation Recovery

   There are three situations that delegation recovery must deal with:

   o   Client reboot or restart

   o   Server reboot or restart

   o   Network partition (full or callback-only)

   In the event the client reboots or restarts, the failure to renew
   leases will result in the revocation of record locks and share
   reservations.  Delegations, however, may be treated a bit
   differently.

   There will be situations in which delegations will need to be
   reestablished after a client reboots or restarts.  The reason for
   this is the client may have file data stored locally and this data
   was associated with the previously held delegations.  The client will
   need to reestablish the appropriate file state on the server.

   To allow for this type of client recovery, the server MAY extend the
   period for delegation recovery beyond the typical lease expiration
   period.  This implies that requests from other clients that conflict
   with these delegations will need to wait.  Because the normal recall
   process may require significant time for the client to flush changed
   state to the server, other clients need be prepared for delays that
   occur because of a conflicting delegation.  This longer interval
   would increase the window for clients to reboot and consult stable
   storage so that the delegations can be reclaimed.  For open
   delegations, such delegations are reclaimed using OPEN with a claim
   type of CLAIM_DELEGATE_PREV.  (See the sections on "Data Caching and
   Revocation" and "Operation 18: OPEN" for discussion of open
   delegation and the details of OPEN respectively).

   A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
   does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM, and
   instead MUST, for a period of time no less than that of the value of
   the lease_time attribute, maintain the client's delegations to allow
   time for the client to issue CLAIM_DELEGATE_PREV requests.  The
   server that supports CLAIM_DELEGATE_PREV MUST support the DELEGPURGE
   operation.




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   When the server reboots or restarts, delegations are reclaimed (using
   the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to
   record locks and share reservations.  However, there is a slight
   semantic difference.  In the normal case if the server decides that a
   delegation should not be granted, it performs the requested action
   (e.g., OPEN) without granting any delegation.  For reclaim, the
   server grants the delegation but a special designation is applied so
   that the client treats the delegation as having been granted but
   recalled by the server.  Because of this, the client has the duty to
   write all modified state to the server and then return the
   delegation.  This process of handling delegation reclaim reconciles
   three principles of the NFS version 4 protocol:

   o  Upon reclaim, a client reporting resources assigned to it by an
      earlier server instance must be granted those resources.

   o  The server has unquestionable authority to determine whether
      delegations are to be granted and, once granted, whether they are
      to be continued.

   o  The use of callbacks is not to be depended upon until the client
      has proven its ability to receive them.

   When a network partition occurs, delegations are subject to freeing
   by the server when the lease renewal period expires.  This is similar
   to the behavior for locks and share reservations.  For delegations,
   however, the server may extend the period in which conflicting
   requests are held off.  Eventually the occurrence of a conflicting
   request from another client will cause revocation of the delegation.
   A loss of the callback path (e.g., by later network configuration
   change) will have the same effect.  A recall request will fail and
   revocation of the delegation will result.

   A client normally finds out about revocation of a delegation when it
   uses a stateid associated with a delegation and receives the error
   NFS4ERR_EXPIRED.  It also may find out about delegation revocation
   after a client reboot when it attempts to reclaim a delegation and
   receives that same error.  Note that in the case of a revoked write
   open delegation, there are issues because data may have been modified
   by the client whose delegation is revoked and separately by other
   clients.  See the section "Revocation Recovery for Write Open
   Delegation" for a discussion of such issues.  Note also that when
   delegations are revoked, information about the revoked delegation
   will be written by the server to stable storage (as described in the
   section "Crash Recovery").  This is done to deal with the case in
   which a server reboots after revoking a delegation but before the
   client holding the revoked delegation is notified about the
   revocation.



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9.3.  Data Caching

   When applications share access to a set of files, they need to be
   implemented so as to take account of the possibility of conflicting
   access by another application.  This is true whether the applications
   in question execute on different clients or reside on the same
   client.

   Share reservations and record locks are the facilities the NFS
   version 4 protocol provides to allow applications to coordinate
   access by providing mutual exclusion facilities.  The NFS version 4
   protocol's data caching must be implemented such that it does not
   invalidate the assumptions that those using these facilities depend
   upon.

9.3.1.  Data Caching and OPENs

   In order to avoid invalidating the sharing assumptions that
   applications rely on, NFS version 4 clients should not provide cached
   data to applications or modify it on behalf of an application when it
   would not be valid to obtain or modify that same data via a READ or
   WRITE operation.

   Furthermore, in the absence of open delegation (see the section "Open
   Delegation") two additional rules apply.  Note that these rules are
   obeyed in practice by many NFS version 2 and version 3 clients.

   o  First, cached data present on a client must be revalidated after
      doing an OPEN.  Revalidating means that the client fetches the
      change attribute from the server, compares it with the cached
      change attribute, and if different, declares the cached data (as
      well as the cached attributes) as invalid.  This is to ensure that
      the data for the OPENed file is still correctly reflected in the
      client's cache.  This validation must be done at least when the
      client's OPEN operation includes DENY=WRITE or BOTH thus
      terminating a period in which other clients may have had the
      opportunity to open the file with WRITE access.  Clients may
      choose to do the revalidation more often (i.e., at OPENs
      specifying DENY=NONE) to parallel the NFS version 3 protocol's
      practice for the benefit of users assuming this degree of cache
      revalidation.

      Since the change attribute is updated for data and metadata
      modifications, some client implementors may be tempted to use the
      time_modify attribute and not change to validate cached data, so
      that metadata changes do not spuriously invalidate clean data.
      The implementor is cautioned in this approach.  The change
      attribute is guaranteed to change for each update to the file,



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      whereas time_modify is guaranteed to change only at the
      granularity of the time_delta attribute.  Use by the client's data
      cache validation logic of time_modify and not change runs the risk
      of the client incorrectly marking stale data as valid.

   o  Second, modified data must be flushed to the server before closing
      a file OPENed for write.  This is complementary to the first rule.
      If the data is not flushed at CLOSE, the revalidation done after
      client OPENs as file is unable to achieve its purpose.  The other
      aspect to flushing the data before close is that the data must be
      committed to stable storage, at the server, before the CLOSE
      operation is requested by the client.  In the case of a server
      reboot or restart and a CLOSEd file, it may not be possible to
      retransmit the data to be written to the file.  Hence, this
      requirement.

9.3.2.  Data Caching and File Locking

   For those applications that choose to use file locking instead of
   share reservations to exclude inconsistent file access, there is an
   analogous set of constraints that apply to client side data caching.
   These rules are effective only if the file locking is used in a way
   that matches in an equivalent way the actual READ and WRITE
   operations executed.  This is as opposed to file locking that is
   based on pure convention.  For example, it is possible to manipulate
   a two-megabyte file by dividing the file into two one-megabyte
   regions and protecting access to the two regions by file locks on
   bytes zero and one.  A lock for write on byte zero of the file would
   represent the right to do READ and WRITE operations on the first
   region.  A lock for write on byte one of the file would represent the
   right to do READ and WRITE operations on the second region.  As long
   as all applications manipulating the file obey this convention, they
   will work on a local filesystem.  However, they may not work with the
   NFS version 4 protocol unless clients refrain from data caching.

   The rules for data caching in the file locking environment are:

   o  First, when a client obtains a file lock for a particular region,
      the data cache corresponding to that region (if any cached data
      exists) must be revalidated.  If the change attribute indicates
      that the file may have been updated since the cached data was
      obtained, the client must flush or invalidate the cached data for
      the newly locked region.  A client might choose to invalidate all
      of non-modified cached data that it has for the file but the only
      requirement for correct operation is to invalidate all of the data
      in the newly locked region.





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   o  Second, before releasing a write lock for a region, all modified
      data for that region must be flushed to the server.  The modified
      data must also be written to stable storage.

   Note that flushing data to the server and the invalidation of cached
   data must reflect the actual byte ranges locked or unlocked.
   Rounding these up or down to reflect client cache block boundaries
   will cause problems if not carefully done.  For example, writing a
   modified block when only half of that block is within an area being
   unlocked may cause invalid modification to the region outside the
   unlocked area.  This, in turn, may be part of a region locked by
   another client.  Clients can avoid this situation by synchronously
   performing portions of write operations that overlap that portion
   (initial or final) that is not a full block.  Similarly, invalidating
   a locked area which is not an integral number of full buffer blocks
   would require the client to read one or two partial blocks from the
   server if the revalidation procedure shows that the data which the
   client possesses may not be valid.

   The data that is written to the server as a prerequisite to the
   unlocking of a region must be written, at the server, to stable
   storage.  The client may accomplish this either with synchronous
   writes or by following asynchronous writes with a COMMIT operation.
   This is required because retransmission of the modified data after a
   server reboot might conflict with a lock held by another client.

   A client implementation may choose to accommodate applications which
   use record locking in non-standard ways (e.g., using a record lock as
   a global semaphore) by flushing to the server more data upon an LOCKU
   than is covered by the locked range.  This may include modified data
   within files other than the one for which the unlocks are being done.
   In such cases, the client must not interfere with applications whose
   READs and WRITEs are being done only within the bounds of record
   locks which the application holds.  For example, an application locks
   a single byte of a file and proceeds to write that single byte.  A
   client that chose to handle a LOCKU by flushing all modified data to
   the server could validly write that single byte in response to an
   unrelated unlock.  However, it would not be valid to write the entire
   block in which that single written byte was located since it includes
   an area that is not locked and might be locked by another client.
   Client implementations can avoid this problem by dividing files with
   modified data into those for which all modifications are done to
   areas covered by an appropriate record lock and those for which there
   are modifications not covered by a record lock.  Any writes done for
   the former class of files must not include areas not locked and thus
   not modified on the client.





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9.3.3.  Data Caching and Mandatory File Locking

   Client side data caching needs to respect mandatory file locking when
   it is in effect.  The presence of mandatory file locking for a given
   file is indicated when the client gets back NFS4ERR_LOCKED from a
   READ or WRITE on a file it has an appropriate share reservation for.
   When mandatory locking is in effect for a file, the client must check
   for an appropriate file lock for data being read or written.  If a
   lock exists for the range being read or written, the client may
   satisfy the request using the client's validated cache.  If an
   appropriate file lock is not held for the range of the read or write,
   the read or write request must not be satisfied by the client's cache
   and the request must be sent to the server for processing.  When a
   read or write request partially overlaps a locked region, the request
   should be subdivided into multiple pieces with each region (locked or
   not) treated appropriately.

9.3.4.  Data Caching and File Identity

   When clients cache data, the file data needs to be organized
   according to the filesystem object to which the data belongs.  For
   NFS version 3 clients, the typical practice has been to assume for
   the purpose of caching that distinct filehandles represent distinct
   filesystem objects.  The client then has the choice to organize and
   maintain the data cache on this basis.

   In the NFS version 4 protocol, there is now the possibility to have
   significant deviations from a "one filehandle per object" model
   because a filehandle may be constructed on the basis of the object's
   pathname.  Therefore, clients need a reliable method to determine if
   two filehandles designate the same filesystem object.  If clients
   were simply to assume that all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between the distinct client side objects
   which mapped to the same server side object.

   By providing a method to differentiate filehandles, the NFS version 4
   protocol alleviates a potential functional regression in comparison
   with the NFS version 3 protocol.  Without this method, caching
   inconsistencies within the same client could occur and this has not
   been present in previous versions of the NFS protocol.  Note that it
   is possible to have such inconsistencies with applications executing
   on multiple clients but that is not the issue being addressed here.

   For the purposes of data caching, the following steps allow an NFS
   version 4 client to determine whether two distinct filehandles denote
   the same server side object:




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   o  If GETATTR directed to two filehandles returns different values of
      the fsid attribute, then the filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches the fsid of the
      two filehandles in question returns a unique_handles attribute
      with a value of TRUE, then the two objects are distinct.

   o  If GETATTR directed to the two filehandles does not return the
      fileid attribute for both of the handles, then it cannot be
      determined whether the two objects are the same.  Therefore,
      operations which depend on that knowledge (e.g., client side data
      caching) cannot be done reliably.

   o  If GETATTR directed to the two filehandles returns different
      values for the fileid attribute, then they are distinct objects.

   o  Otherwise they are the same object.

9.4.  Open Delegation

   When a file is being OPENed, the server may delegate further handling
   of opens and closes for that file to the opening client.  Any such
   delegation is recallable, since the circumstances that allowed for
   the delegation are subject to change.  In particular, the server may
   receive a conflicting OPEN from another client, the server must
   recall the delegation before deciding whether the OPEN from the other
   client may be granted.  Making a delegation is up to the server and
   clients should not assume that any particular OPEN either will or
   will not result in an open delegation.  The following is a typical
   set of conditions that servers might use in deciding whether OPEN
   should be delegated:

   o  The client must be able to respond to the server's callback
      requests.  The server will use the CB_NULL procedure for a test of
      callback ability.

   o  The client must have responded properly to previous recalls.

   o  There must be no current open conflicting with the requested
      delegation.

   o  There should be no current delegation that conflicts with the
      delegation being requested.

   o  The probability of future conflicting open requests should be low
      based on the recent history of the file.




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   o  The existence of any server-specific semantics of OPEN/CLOSE that
      would make the required handling incompatible with the prescribed
      handling that the delegated client would apply (see below).

   There are two types of open delegations, read and write.  A read open
   delegation allows a client to handle, on its own, requests to open a
   file for reading that do not deny read access to others.  Multiple
   read open delegations may be outstanding simultaneously and do not
   conflict.  A write open delegation allows the client to handle, on
   its own, all opens.  Only one write open delegation may exist for a
   given file at a given time and it is inconsistent with any read open
   delegations.

   When a client has a read open delegation, it may not make any changes
   to the contents or attributes of the file but it is assured that no
   other client may do so.  When a client has a write open delegation,
   it may modify the file data since no other client will be accessing
   the file's data.  The client holding a write delegation may only
   affect file attributes which are intimately connected with the file
   data:  size, time_modify, change.

   When a client has an open delegation, it does not send OPENs or
   CLOSEs to the server but updates the appropriate status internally.
   For a read open delegation, opens that cannot be handled locally
   (opens for write or that deny read access) must be sent to the
   server.

   When an open delegation is made, the response to the OPEN contains an
   open delegation structure which specifies the following:

   o  the type of delegation (read or write)

   o  space limitation information to control flushing of data on close
      (write open delegation only, see the section "Open Delegation and
      Data Caching")

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the delegation for READ and WRITE

   The delegation stateid is separate and distinct from the stateid for
   the OPEN proper.  The standard stateid, unlike the delegation
   stateid, is associated with a particular lock_owner and will continue
   to be valid after the delegation is recalled and the file remains
   open.






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   When a request internal to the client is made to open a file and open
   delegation is in effect, it will be accepted or rejected solely on
   the basis of the following conditions.  Any requirement for other
   checks to be made by the delegate should result in open delegation
   being denied so that the checks can be made by the server itself.

   o  The access and deny bits for the request and the file as described
      in the section "Share Reservations".

   o  The read and write permissions as determined below.

   The nfsace4 passed with delegation can be used to avoid frequent
   ACCESS calls.  The permission check should be as follows:

   o  If the nfsace4 indicates that the open may be done, then it should
      be granted without reference to the server.

   o  If the nfsace4 indicates that the open may not be done, then an
      ACCESS request must be sent to the server to obtain the definitive
      answer.

   The server may return an nfsace4 that is more restrictive than the
   actual ACL of the file.  This includes an nfsace4 that specifies
   denial of all access.  Note that some common practices such as
   mapping the traditional user "root" to the user "nobody" may make it
   incorrect to return the actual ACL of the file in the delegation
   response.

   The use of delegation together with various other forms of caching
   creates the possibility that no server authentication will ever be
   performed for a given user since all of the user's requests might be
   satisfied locally.  Where the client is depending on the server for
   authentication, the client should be sure authentication occurs for
   each user by use of the ACCESS operation.  This should be the case
   even if an ACCESS operation would not be required otherwise.  As
   mentioned before, the server may enforce frequent authentication by
   returning an nfsace4 denying all access with every open delegation.

9.4.1.  Open Delegation and Data Caching

   OPEN delegation allows much of the message overhead associated with
   the opening and closing files to be eliminated.  An open when an open
   delegation is in effect does not require that a validation message be
   sent to the server.  The continued endurance of the "read open
   delegation" provides a guarantee that no OPEN for write and thus no
   write has occurred.  Similarly, when closing a file opened for write
   and if write open delegation is in effect, the data written does not
   have to be flushed to the server until the open delegation is



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   recalled.  The continued endurance of the open delegation provides a
   guarantee that no open and thus no read or write has been done by
   another client.

   For the purposes of open delegation, READs and WRITEs done without an
   OPEN are treated as the functional equivalents of a corresponding
   type of OPEN.  This refers to the READs and WRITEs that use the
   special stateids consisting of all zero bits or all one bits.
   Therefore, READs or WRITEs with a special stateid done by another
   client will force the server to recall a write open delegation.  A
   WRITE with a special stateid done by another client will force a
   recall of read open delegations.

   With delegations, a client is able to avoid writing data to the
   server when the CLOSE of a file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of
   stable storage for the modified file data generated by the
   application.  At the close, file data is written to the server and
   through normal accounting the server is able to determine if the
   available filesystem space for the data has been exceeded (i.e.,
   server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that a
   alternative method be in place for the same type of communication to
   occur between client and server.

   In the delegation response, the server provides either the limit of
   the size of the file or the number of modified blocks and associated
   block size.  The server must ensure that the client will be able to
   flush data to the server of a size equal to that provided in the
   original delegation.  The server must make this assurance for all
   outstanding delegations.  Therefore, the server must be careful in
   its management of available space for new or modified data taking
   into account available filesystem space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available filesystem space.  The client should abide by the server's
   state space limits for delegations.  If the client exceeds the stated
   limits for the delegation, the server's behavior is undefined.

   Based on server conditions, quotas or available filesystem space, the
   server may grant write open delegations with very restrictive space
   limitations.  The limitations may be defined in a way that will
   always force modified data to be flushed to the server on close.

   With respect to authentication, flushing modified data to the server
   after a CLOSE has occurred may be problematic.  For example, the user
   of the application may have logged off the client and unexpired
   authentication credentials may not be present.  In this case, the
   client may need to take special care to ensure that local unexpired



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   credentials will in fact be available.  This may be accomplished by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration or by making private copies of
   credentials to assure their availability when needed.

9.4.2.  Open Delegation and File Locks

   When a client holds a write open delegation, lock operations may be
   performed locally.  This includes those required for mandatory file
   locking.  This can be done since the delegation implies that there
   can be no conflicting locks.  Similarly, all of the revalidations
   that would normally be associated with obtaining locks and the
   flushing of data associated with the releasing of locks need not be
   done.

   When a client holds a read open delegation, lock operations are not
   performed locally.  All lock operations, including those requesting
   non-exclusive locks, are sent to the server for resolution.

9.4.3.  Handling of CB_GETATTR

   The server needs to employ special handling for a GETATTR where the
   target is a file that has a write open delegation in effect.  The
   reason for this is that the client holding the write delegation may
   have modified the data and the server needs to reflect this change to
   the second client that submitted the GETATTR.  Therefore, the client
   holding the write delegation needs to be interrogated.  The server
   will use the CB_GETATTR operation.  The only attributes that the
   server can reliably query via CB_GETATTR are size and change.

   Since CB_GETATTR is being used to satisfy another client's GETATTR
   request, the server only needs to know if the client holding the
   delegation has a modified version of the file.  If the client's copy
   of the delegated file is not modified (data or size), the server can
   satisfy the second client's GETATTR request from the attributes
   stored locally at the server.  If the file is modified, the server
   only needs to know about this modified state.  If the server
   determines that the file is currently modified, it will respond to
   the second client's GETATTR as if the file had been modified locally
   at the server.

   Since the form of the change attribute is determined by the server
   and is opaque to the client, the client and server need to agree on a
   method of communicating the modified state of the file.  For the size
   attribute, the client will report its current view of the file size.

   For the change attribute, the handling is more involved.




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   For the client, the following steps will be taken when receiving a
   write delegation:

   o  The value of the change attribute will be obtained from the server
      and cached.  Let this value be represented by c.

   o  The client will create a value greater than c that will be used
      for communicating modified data is held at the client.  Let this
      value be represented by d.

   o  When the client is queried via CB_GETATTR for the change
      attribute, it checks to see if it holds modified data.  If the
      file is modified, the value d is returned for the change attribute
      value.  If this file is not currently modified, the client returns
      the value c for the change attribute.

   For simplicity of implementation, the client MAY for each CB_GETATTR
   return the same value d.  This is true even if, between successive
   CB_GETATTR operations, the client again modifies in the file's data
   or metadata in its cache.  The client can return the same value
   because the only requirement is that the client be able to indicate
   to the server that the client holds modified data.  Therefore, the
   value of d may always be c + 1.

   While the change attribute is opaque to the client in the sense that
   it has no idea what units of time, if any, the server is counting
   change with, it is not opaque in that the client has to treat it as
   an unsigned integer, and the server has to be able to see the results
   of the client's changes to that integer.  Therefore, the server MUST
   encode the change attribute in network order when sending it to the
   client.  The client MUST decode it from network order to its native
   order when receiving it and the client MUST encode it network order
   when sending it to the server.  For this reason, change is defined as
   an unsigned integer rather than an opaque array of octets.

   For the server, the following steps will be taken when providing a
   write delegation:

   o  Upon providing a write delegation, the server will cache a copy of
      the change attribute in the data structure it uses to record the
      delegation.  Let this value be represented by sc.

   o  When a second client sends a GETATTR operation on the same file to
      the server, the server obtains the change attribute from the first
      client.  Let this value be cc.






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   o  If the value cc is equal to sc, the file is not modified and the
      server returns the current values for change, time_metadata, and
      time_modify (for example) to the second client.

   o  If the value cc is NOT equal to sc, the file is currently modified
      at the first client and most likely will be modified at the server
      at a future time.  The server then uses its current time to
      construct attribute values for time_metadata and time_modify.  A
      new value of sc, which we will call nsc, is computed by the
      server, such that nsc >= sc + 1.  The server then returns the
      constructed time_metadata, time_modify, and nsc values to the
      requester.  The server replaces sc in the delegation record with
      nsc.  To prevent the possibility of time_modify, time_metadata,
      and change from appearing to go backward (which would happen if
      the client holding the delegation fails to write its modified data
      to the server before the delegation is revoked or returned), the
      server SHOULD update the file's metadata record with the
      constructed attribute values.  For reasons of reasonable
      performance, committing the constructed attribute values to stable
      storage is OPTIONAL.

      As discussed earlier in this section, the client MAY return the
      same cc value on subsequent CB_GETATTR calls, even if the file was
      modified in the client's cache yet again between successive
      CB_GETATTR calls.  Therefore, the server must assume that the file
      has been modified yet again, and MUST take care to ensure that the
      new nsc it constructs and returns is greater than the previous nsc
      it returned.  An example implementation's delegation record would
      satisfy this mandate by including a boolean field (let us call it
      "modified") that is set to false when the delegation is granted,
      and an sc value set at the time of grant to the change attribute
      value.  The modified field would be set to true the first time cc
      != sc, and would stay true until the delegation is returned or
      revoked.  The processing for constructing nsc, time_modify, and
      time_metadata would use this pseudo code:

      if (!modified) {
          do CB_GETATTR for change and size;

             if (cc != sc)
                 modified = TRUE;
         } else {
                 do CB_GETATTR for size;
         }

         if (modified) {
             sc = sc + 1;
          time_modify = time_metadata = current_time;



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          update sc, time_modify, time_metadata into file's metadata;
      }

      return to client (that sent GETATTR) the attributes
         it requested, but make sure size comes from what
         CB_GETATTR returned.  Do not update the file's metadata
         with the client's modified size.

   o  In the case that the file attribute size is different than the
      server's current value, the server treats this as a modification
      regardless of the value of the change attribute retrieved via
      CB_GETATTR and responds to the second client as in the last step.

   This methodology resolves issues of clock differences between client
   and server and other scenarios where the use of CB_GETATTR break
   down.

   It should be noted that the server is under no obligation to use
   CB_GETATTR and therefore the server MAY simply recall the delegation
   to avoid its use.

9.4.4.  Recall of Open Delegation

   The following events necessitate recall of an open delegation:

   o  Potentially conflicting OPEN request (or READ/WRITE done with
      "special" stateid)

   o  SETATTR issued by another client

   o  REMOVE request for the file

   o  RENAME request for the file as either source or target of the
      RENAME

   Whether a RENAME of a directory in the path leading to the file
   results in recall of an open delegation depends on the semantics of
   the server filesystem.  If that filesystem denies such RENAMEs when a
   file is open, the recall must be performed to determine whether the
   file in question is, in fact, open.

   In addition to the situations above, the server may choose to recall
   open delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for the
   possibility of recall.






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   When a client receives a recall for an open delegation, it needs to
   update state on the server before returning the delegation.  These
   same updates must be done whenever a client chooses to return a
   delegation voluntarily.  The following items of state need to be
   dealt with:

   o  If the file associated with the delegation is no longer open and
      no previous CLOSE operation has been sent to the server, a CLOSE
      operation must be sent to the server.

   o  If a file has other open references at the client, then OPEN
      operations must be sent to the server.  The appropriate stateids
      will be provided by the server for subsequent use by the client
      since the delegation stateid will not longer be valid.  These OPEN
      requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
      will allow the presentation of the delegation stateid so that the
      client can establish the appropriate rights to perform the OPEN.
      (see the section "Operation 18: OPEN" for details.)

   o  If there are granted file locks, the corresponding LOCK operations
      need to be performed.  This applies to the write open delegation
      case only.

   o  For a write open delegation, if at the time of recall the file is
      not open for write, all modified data for the file must be flushed
      to the server.  If the delegation had not existed, the client
      would have done this data flush before the CLOSE operation.

   o  For a write open delegation when a file is still open at the time
      of recall, any modified data for the file needs to be flushed to
      the server.

   o  With the write open delegation in place, it is possible that the
      file was truncated during the duration of the delegation.  For
      example, the truncation could have occurred as a result of an OPEN
      UNCHECKED with a size attribute value of zero.  Therefore, if a
      truncation of the file has occurred and this operation has not
      been propagated to the server, the truncation must occur before
      any modified data is written to the server.

   In the case of write open delegation, file locking imposes some
   additional requirements.  To precisely maintain the associated
   invariant, it is required to flush any modified data in any region
   for which a write lock was released while the write delegation was in
   effect.  However, because the write open delegation implies no other
   locking by other clients, a simpler implementation is to flush all
   modified data for the file (as described just above) if any write
   lock has been released while the write open delegation was in effect.



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   An implementation need not wait until delegation recall (or deciding
   to voluntarily return a delegation) to perform any of the above
   actions, if implementation considerations (e.g., resource
   availability constraints) make that desirable.  Generally, however,
   the fact that the actual open state of the file may continue to
   change makes it not worthwhile to send information about opens and
   closes to the server, except as part of delegation return.  Only in
   the case of closing the open that resulted in obtaining the
   delegation would clients be likely to do this early, since, in that
   case, the close once done will not be undone.  Regardless of the
   client's choices on scheduling these actions, all must be performed
   before the delegation is returned, including (when applicable) the
   close that corresponds to the open that resulted in the delegation.
   These actions can be performed either in previous requests or in
   previous operations in the same COMPOUND request.

9.4.5.  Clients that Fail to Honor Delegation Recalls

   A client may fail to respond to a recall for various reasons, such as
   a failure of the callback path from server to the client.  The client
   may be unaware of a failure in the callback path.  This lack of
   awareness could result in the client finding out long after the
   failure that its delegation has been revoked, and another client has
   modified the data for which the client had a delegation.  This is
   especially a problem for the client that held a write delegation.

   The server also has a dilemma in that the client that fails to
   respond to the recall might also be sending other NFS requests,
   including those that renew the lease before the lease expires.
   Without returning an error for those lease renewing operations, the
   server leads the client to believe that the delegation it has is in
   force.

   This difficulty is solved by the following rules:

   o  When the callback path is down, the server MUST NOT revoke the
      delegation if one of the following occurs:

      -  The client has issued a RENEW operation and the server has
         returned an NFS4ERR_CB_PATH_DOWN error.  The server MUST renew
         the lease for any record locks and share reservations the
         client has that the server has known about (as opposed to those
         locks and share reservations the client has established but not
         yet sent to the server, due to the delegation).  The server
         SHOULD give the client a reasonable time to return its
         delegations to the server before revoking the client's
         delegations.




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      -  The client has not issued a RENEW operation for some period of
         time after the server attempted to recall the delegation.  This
         period of time MUST NOT be less than the value of the
         lease_time attribute.

   o  When the client holds a delegation, it can not rely on operations,
      except for RENEW, that take a stateid, to renew delegation leases
      across callback path failures.  The client that wants to keep
      delegations in force across callback path failures must use RENEW
      to do so.

9.4.6.  Delegation Revocation

   At the point a delegation is revoked, if there are associated opens
   on the client, the applications holding these opens need to be
   notified.  This notification usually occurs by returning errors for
   READ/WRITE operations or when a close is attempted for the open file.

   If no opens exist for the file at the point the delegation is
   revoked, then notification of the revocation is unnecessary.
   However, if there is modified data present at the client for the
   file, the user of the application should be notified.  Unfortunately,
   it may not be possible to notify the user since active applications
   may not be present at the client.  See the section "Revocation
   Recovery for Write Open Delegation" for additional details.

9.5.  Data Caching and Revocation

   When locks and delegations are revoked, the assumptions upon which
   successful caching depend are no longer guaranteed.  For any locks or
   share reservations that have been revoked, the corresponding owner
   needs to be notified.  This notification includes applications with a
   file open that has a corresponding delegation which has been revoked.
   Cached data associated with the revocation must be removed from the
   client.  In the case of modified data existing in the client's cache,
   that data must be removed from the client without it being written to
   the server.  As mentioned, the assumptions made by the client are no
   longer valid at the point when a lock or delegation has been revoked.
   For example, another client may have been granted a conflicting lock
   after the revocation of the lock at the first client.  Therefore, the
   data within the lock range may have been modified by the other
   client.  Obviously, the first client is unable to guarantee to the
   application what has occurred to the file in the case of revocation.

   Notification to a lock owner will in many cases consist of simply
   returning an error on the next and all subsequent READs/WRITEs to the
   open file or on the close.  Where the methods available to a client
   make such notification impossible because errors for certain



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   operations may not be returned, more drastic action such as signals
   or process termination may be appropriate.  The justification for
   this is that an invariant for which an application depends on may be
   violated.  Depending on how errors are typically treated for the
   client operating environment, further levels of notification
   including logging, console messages, and GUI pop-ups may be
   appropriate.

9.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery for a write open delegation poses the special
   issue of modified data in the client cache while the file is not
   open.  In this situation, any client which does not flush modified
   data to the server on each close must ensure that the user receives
   appropriate notification of the failure as a result of the
   revocation.  Since such situations may require human action to
   correct problems, notification schemes in which the appropriate user
   or administrator is notified may be necessary.  Logging and console
   messages are typical examples.

   If there is modified data on the client, it must not be flushed
   normally to the server.  A client may attempt to provide a copy of
   the file data as modified during the delegation under a different
   name in the filesystem name space to ease recovery.  Note that when
   the client can determine that the file has not been modified by any
   other client, or when the client has a complete cached copy of file
   in question, such a saved copy of the client's view of the file may
   be of particular value for recovery.  In other case, recovery using a
   copy of the file based partially on the client's cached data and
   partially on the server copy as modified by other clients, will be
   anything but straightforward, so clients may avoid saving file
   contents in these situations or mark the results specially to warn
   users of possible problems.

   Saving of such modified data in delegation revocation situations may
   be limited to files of a certain size or might be used only when
   sufficient disk space is available within the target filesystem.
   Such saving may also be restricted to situations when the client has
   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target filesystem.

9.6.  Attribute Caching

   The attributes discussed in this section do not include named
   attributes.  Individual named attributes are analogous to files and
   caching of the data for these needs to be handled just as data





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   caching is for ordinary files.  Similarly, LOOKUP results from an
   OPENATTR directory are to be cached on the same basis as any other
   pathnames and similarly for directory contents.

   Clients may cache file attributes obtained from the server and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through in that modification to file attributes is always done by
   means of requests to the server and should not be done locally and
   cached.  The exception to this are modifications to attributes that
   are intimately connected with data caching.  Therefore, extending a
   file by writing data to the local data cache is reflected immediately
   in the size as seen on the client without this change being
   immediately reflected on the server.  Normally such changes are not
   propagated directly to the server but when the modified data is
   flushed to the server, analogous attribute changes are made on the
   server.  When open delegation is in effect, the modified attributes
   may be returned to the server in the response to a CB_RECALL call.

   The result of local caching of attributes is that the attribute
   caches maintained on individual clients will not be coherent.
   Changes made in one order on the server may be seen in a different
   order on one client and in a third order on a different client.

   The typical filesystem application programming interfaces do not
   provide means to atomically modify or interrogate attributes for
   multiple files at the same time.  The following rules provide an
   environment where the potential incoherences mentioned above can be
   reasonably managed.  These rules are derived from the practice of
   previous NFS protocols.

   o  All attributes for a given file (per-fsid attributes excepted) are
      cached as a unit at the client so that no non-serializability can
      arise within the context of a single file.

   o  An upper time boundary is maintained on how long a client cache
      entry can be kept without being refreshed from the server.

   o  When operations are performed that change attributes at the
      server, the updated attribute set is requested as part of the
      containing RPC.  This includes directory operations that update
      attributes indirectly.  This is accomplished by following the
      modifying operation with a GETATTR operation and then using the
      results of the GETATTR to update the client's cached attributes.

   Note that if the full set of attributes to be cached is requested by
   READDIR, the results can be cached by the client on the same basis as
   attributes obtained via GETATTR.




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   A client may validate its cached version of attributes for a file by
   fetching just both the change and time_access attributes and assuming
   that if the change attribute has the same value as it did when the
   attributes were cached, then no attributes other than time_access
   have changed.  The reason why time_access is also fetched is because
   many servers operate in environments where the operation that updates
   change does not update time_access.  For example, POSIX file
   semantics do not update access time when a file is modified by the
   write system call.  Therefore, the client that wants a current
   time_access value should fetch it with change during the attribute
   cache validation processing and update its cached time_access.

   The client may maintain a cache of modified attributes for those
   attributes intimately connected with data of modified regular files
   (size, time_modify, and change).  Other than those three attributes,
   the client MUST NOT maintain a cache of modified attributes.
   Instead, attribute changes are immediately sent to the server.

   In some operating environments, the equivalent to time_access is
   expected to be implicitly updated by each read of the content of the
   file object.  If an NFS client is caching the content of a file
   object, whether it is a regular file, directory, or symbolic link,
   the client SHOULD NOT update the time_access attribute (via SETATTR
   or a small READ or READDIR request) on the server with each read that
   is satisfied from cache.  The reason is that this can defeat the
   performance benefits of caching content, especially since an explicit
   SETATTR of time_access may alter the change attribute on the server.
   If the change attribute changes, clients that are caching the content
   will think the content has changed, and will re-read unmodified data
   from the server.  Nor is the client encouraged to maintain a modified
   version of time_access in its cache, since this would mean that the
   client will either eventually have to write the access time to the
   server with bad performance effects, or it would never update the
   server's time_access, thereby resulting in a situation where an
   application that caches access time between a close and open of the
   same file observes the access time oscillating between the past and
   present.  The time_access attribute always means the time of last
   access to a file by a read that was satisfied by the server.  This
   way clients will tend to see only time_access changes that go forward
   in time.

9.7.  Data and Metadata Caching and Memory Mapped Files

   Some operating environments include the capability for an application
   to map a file's content into the application's address space.  Each
   time the application accesses a memory location that corresponds to a
   block that has not been loaded into the address space, a page fault
   occurs and the file is read (or if the block does not exist in the



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   file, the block is allocated and then instantiated in the
   application's address space).

   As long as each memory mapped access to the file requires a page
   fault, the relevant attributes of the file that are used to detect
   access and modification (time_access, time_metadata, time_modify, and
   change) will be updated.  However, in many operating environments,
   when page faults are not required these attributes will not be
   updated on reads or updates to the file via memory access (regardless
   whether the file is local file or is being access remotely).  A
   client or server MAY fail to update attributes of a file that is
   being accessed via memory mapped I/O.  This has several implications:

   o  If there is an application on the server that has memory mapped a
      file that a client is also accessing, the client may not be able
      to get a consistent value of the change attribute to determine
      whether its cache is stale or not.  A server that knows that the
      file is memory mapped could always pessimistically return updated
      values for change so as to force the application to always get the
      most up to date data and metadata for the file.  However, due to
      the negative performance implications of this, such behavior is
      OPTIONAL.

   o  If the memory mapped file is not being modified on the server, and
      instead is just being read by an application via the memory mapped
      interface, the client will not see an updated time_access
      attribute.  However, in many operating environments, neither will
      any process running on the server.  Thus NFS clients are at no
      disadvantage with respect to local processes.

   o  If there is another client that is memory mapping the file, and if
      that client is holding a write delegation, the same set of issues
      as discussed in the previous two bullet items apply.  So, when a
      server does a CB_GETATTR to a file that the client has modified in
      its cache, the response from CB_GETATTR will not necessarily be
      accurate.  As discussed earlier, the client's obligation is to
      report that the file has been modified since the delegation was
      granted, not whether it has been modified again between successive
      CB_GETATTR calls, and the server MUST assume that any file the
      client has modified in cache has been modified again between
      successive CB_GETATTR calls.  Depending on the nature of the
      client's memory management system, this weak obligation may not be
      possible.  A client MAY return stale information in CB_GETATTR
      whenever the file is memory mapped.

   o  The mixture of memory mapping and file locking on the same file is
      problematic.  Consider the following scenario, where the page size
      on each client is 8192 bytes.



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      -  Client A memory maps first page (8192 bytes) of file X

      -  Client B memory maps first page (8192 bytes) of file X

      -  Client A write locks first 4096 bytes

      -  Client B write locks second 4096 bytes

      -  Client A, via a STORE instruction modifies part of its locked
         region.

      -  Simultaneous to client A, client B issues a STORE on part of
         its locked region.

   Here the challenge is for each client to resynchronize to get a
   correct view of the first page.  In many operating environments, the
   virtual memory management systems on each client only know a page is
   modified, not that a subset of the page corresponding to the
   respective lock regions has been modified.  So it is not possible for
   each client to do the right thing, which is to only write to the
   server that portion of the page that is locked. For example, if
   client A simply writes out the page, and then client B writes out the
   page, client A's data is lost.

   Moreover, if mandatory locking is enabled on the file, then we have a
   different problem.  When clients A and B issue the STORE
   instructions, the resulting page faults require a record lock on the
   entire page.  Each client then tries to extend their locked range to
   the entire page, which results in a deadlock.

   Communicating the NFS4ERR_DEADLOCK error to a STORE instruction is
   difficult at best.

   If a client is locking the entire memory mapped file, there is no
   problem with advisory or mandatory record locking, at least until the
   client unlocks a region in the middle of the file.

   Given the above issues the following are permitted:

   -  Clients and servers MAY deny memory mapping a file they know there
      are record locks for.

   -  Clients and servers MAY deny a record lock on a file they know is
      memory mapped.







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   -  A client MAY deny memory mapping a file that it knows requires
      mandatory locking for I/O.  If mandatory locking is enabled after
      the file is opened and mapped, the client MAY deny the application
      further access to its mapped file.

9.8.  Name Caching

   The results of LOOKUP and READDIR operations may be cached to avoid
   the cost of subsequent LOOKUP operations.  Just as in the case of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate the effects of these inconsistencies and given
   the context of typical filesystem APIs, an upper time boundary is
   maintained on how long a client name cache entry can be kept without
   verifying that the entry has not been made invalid by a directory
   change operation performed by another client.

   When a client is not making changes to a directory for which there
   exist name cache entries, the client needs to periodically fetch
   attributes for that directory to ensure that it is not being
   modified.  After determining that no modification has occurred, the
   expiration time for the associated name cache entries may be updated
   to be the current time plus the name cache staleness bound.

   When a client is making changes to a given directory, it needs to
   determine whether there have been changes made to the directory by
   other clients.  It does this by using the change attribute as
   reported before and after the directory operation in the associated
   change_info4 value returned for the operation.  The server is able to
   communicate to the client whether the change_info4 data is provided
   atomically with respect to the directory operation.  If the change
   values are provided atomically, the client is then able to compare
   the pre-operation change value with the change value in the client's
   name cache.  If the comparison indicates that the directory was
   updated by another client, the name cache associated with the
   modified directory is purged from the client.  If the comparison
   indicates no modification, the name cache can be updated on the
   client to reflect the directory operation and the associated timeout
   extended.  The post-operation change value needs to be saved as the
   basis for future change_info4 comparisons.

   As demonstrated by the scenario above, name caching requires that the
   client revalidate name cache data by inspecting the change attribute
   of a directory at the point when the name cache item was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre and post
   operation change attribute values atomically.  When the server is



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   unable to report the before and after values atomically with respect
   to the directory operation, the server must indicate that fact in the
   change_info4 return value.  When the information is not atomically
   reported, the client should not assume that other clients have not
   changed the directory.

9.9.  Directory Caching

   The results of READDIR operations may be used to avoid subsequent
   READDIR operations.  Just as in the cases of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate the effects of these inconsistencies, and given the
   context of typical filesystem APIs, the following rules should be
   followed:

   o  Cached READDIR information for a directory which is not obtained
      in a single READDIR operation must always be a consistent snapshot
      of directory contents.  This is determined by using a GETATTR
      before the first READDIR and after the last of READDIR that
      contributes to the cache.

   o  An upper time boundary is maintained to indicate the length of
      time a directory cache entry is considered valid before the client
      must revalidate the cached information.

   The revalidation technique parallels that discussed in the case of
   name caching.  When the client is not changing the directory in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime of the cache entry can be extended at
   these checkpoints.  When a client is modifying the directory, the
   client needs to use the change_info4 data to determine whether there
   are other clients modifying the directory.  If it is determined that
   no other client modifications are occurring, the client may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that the
   client revalidate directory cache data by inspecting the change
   attribute of a directory at the point when the directory was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre and post
   operation change attribute values atomically.  When the server is
   unable to report the before and after values atomically with respect
   to the directory operation, the server must indicate that fact in the
   change_info4 return value.  When the information is not atomically
   reported, the client should not assume that other clients have not
   changed the directory.



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10.  Minor Versioning

   To address the requirement of an NFS protocol that can evolve as the
   need arises, the NFS version 4 protocol contains the rules and
   framework to allow for future minor changes or versioning.

   The base assumption with respect to minor versioning is that any
   future accepted minor version must follow the IETF process and be
   documented in a standards track RFC.  Therefore, each minor version
   number will correspond to an RFC.  Minor version zero of the NFS
   version 4 protocol is represented by this RFC.  The COMPOUND
   procedure will support the encoding of the minor version being
   requested by the client.

   The following items represent the basic rules for the development of
   minor versions.  Note that a future minor version may decide to
   modify or add to the following rules as part of the minor version
   definition.

    1.  Procedures are not added or deleted

        To maintain the general RPC model, NFS version 4 minor versions
        will not add to or delete procedures from the NFS program.

    2.  Minor versions may add operations to the COMPOUND and
        CB_COMPOUND procedures.

        The addition of operations to the COMPOUND and CB_COMPOUND
        procedures does not affect the RPC model.

    2.1 Minor versions may append attributes to GETATTR4args, bitmap4,
        and GETATTR4res.

        This allows for the expansion of the attribute model to allow
        for future growth or adaptation.

    2.2 Minor version X must append any new attributes after the last
        documented attribute.

        Since attribute results are specified as an opaque array of
        per-attribute XDR encoded results, the complexity of adding new
        attributes in the midst of the current definitions will be too
        burdensome.

    3.  Minor versions must not modify the structure of an existing
        operation's arguments or results.





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        Again the complexity of handling multiple structure definitions
        for a single operation is too burdensome.  New operations should
        be added instead of modifying existing structures for a minor
        version.

        This rule does not preclude the following adaptations in a minor
        version.

      o  adding bits to flag fields such as new attributes to GETATTR's
         bitmap4 data type

      o  adding bits to existing attributes like ACLs that have flag
         words

      o  extending enumerated types (including NFS4ERR_*) with new
         values

    4.  Minor versions may not modify the structure of existing
        attributes.

    5.  Minor versions may not delete operations.

        This prevents the potential reuse of a particular operation
        "slot" in a future minor version.

    6.  Minor versions may not delete attributes.

    7.  Minor versions may not delete flag bits or enumeration values.

    8.  Minor versions may declare an operation as mandatory to NOT
        implement.

        Specifying an operation as "mandatory to not implement" is
        equivalent to obsoleting an operation.  For the client, it means
        that the operation should not be sent to the server.  For the
        server, an NFS error can be returned as opposed to "dropping"
        the request as an XDR decode error.  This approach allows for
        the obsolescence of an operation while maintaining its structure
        so that a future minor version can reintroduce the operation.

    8.1 Minor versions may declare attributes mandatory to NOT
        implement.

    8.2 Minor versions may declare flag bits or enumeration values as
        mandatory to NOT implement.

    9.  Minor versions may downgrade features from mandatory to
        recommended, or recommended to optional.



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    10. Minor versions may upgrade features from optional to recommended
        or recommended to mandatory.

    11. A client and server that support minor version X must support
        minor versions 0 (zero) through X-1 as well.

    12. No new features may be introduced as mandatory in a minor
        version.

        This rule allows for the introduction of new functionality and
        forces the use of implementation experience before designating a
        feature as mandatory.

    13. A client MUST NOT attempt to use a stateid, filehandle, or
        similar returned object from the COMPOUND procedure with minor
        version X for another COMPOUND procedure with minor version Y,
        where X != Y.

11.  Internationalization

   The primary issue in which NFS version 4 needs to deal with
   internationalization, or I18N, is with respect to file names and
   other strings as used within the protocol.  The choice of string
   representation must allow reasonable name/string access to clients
   which use various languages.  The UTF-8 encoding of the UCS as
   defined by [ISO10646] allows for this type of access and follows the
   policy described in "IETF Policy on Character Sets and Languages",
   [RFC2277].

   [RFC3454], otherwise know as "stringprep", documents a framework for
   using Unicode/UTF-8 in networking protocols, so as "to increase the
   likelihood that string input and string comparison work in ways that
   make sense for typical users throughout the world."  A protocol must
   define a profile of stringprep "in order to fully specify the
   processing options."  The remainder of this Internationalization
   section defines the NFS version 4 stringprep profiles.  Much of
   terminology used for the remainder of this section comes from
   stringprep.

   There are three UTF-8 string types defined for NFS version 4:
   utf8str_cs, utf8str_cis, and utf8str_mixed.  Separate profiles are
   defined for each. Each profile defines the following, as required by
   stringprep:

   o  The intended applicability of the profile






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   o  The character repertoire that is the input and output to
      stringprep (which is Unicode 3.2 for referenced version of
      stringprep)

   o  The mapping tables from stringprep used (as described in section 3
      of stringprep)

   o  Any additional mapping tables specific to the profile

   o  The Unicode normalization used, if any (as described in section 4
      of stringprep)

   o  The tables from stringprep listing of characters that are
      prohibited as output (as described in section 5 of stringprep)

   o  The bidirectional string testing used, if any (as described in
      section 6 of stringprep)

   o  Any additional characters that are prohibited as output specific
      to the profile

   Stringprep discusses Unicode characters, whereas NFS version 4
   renders UTF-8 characters.  Since there is a one to one mapping from
   UTF-8 to Unicode, where ever the remainder of this document refers to
   to Unicode, the reader should assume UTF-8.

   Much of the text for the profiles comes from [RFC3454].

11.1.  Stringprep profile for the utf8str_cs type

   Every use of the utf8str_cs type definition in the NFS version 4
   protocol specification follows the profile named nfs4_cs_prep.

11.1.1.  Intended applicability of the nfs4_cs_prep profile

   The utf8str_cs type is a case sensitive string of UTF-8 characters.
   Its primary use in NFS Version 4 is for naming components and
   pathnames.  Components and pathnames are stored on the server's
   filesystem.  Two valid distinct UTF-8 strings might be the same after
   processing via the utf8str_cs profile.  If the strings are two names
   inside a directory, the NFS version 4 server will need to either:

   o  disallow the creation of a second name if it's post processed form
      collides with that of an existing name, or

   o  allow the creation of the second name, but arrange so that after
      post processing, the second name is different than the post
      processed form of the first name.



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11.1.2.  Character repertoire of nfs4_cs_prep

   The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
   Appendix A.1

11.1.3.  Mapping used by nfs4_cs_prep

   The nfs4_cs_prep profile specifies mapping using the following tables
   from stringprep:

      Table B.1

   Table B.2 is normally not part of the nfs4_cs_prep profile as it is
   primarily for dealing with case-insensitive comparisons.  However, if
   the NFS version 4 file server supports the case_insensitive
   filesystem attribute, and if case_insensitive is true, the NFS
   version 4 server MUST use Table B.2 (in addition to Table B1) when
   processing utf8str_cs strings, and the NFS version 4 client MUST
   assume Table B.2 (in addition to Table B.1) are being used.

   If the case_preserving attribute is present and set to false, then
   the NFS version 4 server MUST use table B.2 to map case when
   processing utf8str_cs strings.  Whether the server maps from lower to
   upper case or the upper to lower case is an implementation
   dependency.

11.1.4.  Normalization used by nfs4_cs_prep

   The nfs4_cs_prep profile does not specify a normalization form.  A
   later revision of this specification may specify a particular
   normalization form.  Therefore, the server and client can expect that
   they may receive unnormalized characters within protocol requests and
   responses.  If the operating environment requires normalization, then
   the implementation must normalize utf8str_cs strings within the
   protocol before presenting the information to an application (at the
   client) or local filesystem (at the server).















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11.1.5.  Prohibited output for nfs4_cs_prep

   The nfs4_cs_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.3
      Table C.4
      Table C.5
      Table C.6
      Table C.7
      Table C.8
      Table C.9

11.1.6.  Bidirectional output for nfs4_cs_prep

   The nfs4_cs_prep profile does not specify any checking of
   bidirectional strings.

11.2.  Stringprep profile for the utf8str_cis type

   Every use of the utf8str_cis type definition in the NFS version 4
   protocol specification follows the profile named nfs4_cis_prep.

11.2.1.  Intended applicability of the nfs4_cis_prep profile

   The utf8str_cis type is a case insensitive string of UTF-8
   characters.  Its primary use in NFS Version 4 is for naming NFS
   servers.

11.2.2.  Character repertoire of nfs4_cis_prep

   The nfs4_cis_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1

11.2.3.  Mapping used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies mapping using the following
   tables from stringprep:

      Table B.1
      Table B.2

11.2.4.  Normalization used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies using Unicode normalization form
   KC, as described in stringprep.





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11.2.5.  Prohibited output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2
      Table C.2.2
      Table C.3
      Table C.4
      Table C.5
      Table C.6
      Table C.7
      Table C.8
      Table C.9

11.2.6.  Bidirectional output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies checking bidirectional strings as
   described in stringprep's section 6.

11.3.  Stringprep profile for the utf8str_mixed type

   Every use of the utf8str_mixed type definition in the NFS version 4
   protocol specification follows the profile named nfs4_mixed_prep.

11.3.1.  Intended applicability of the nfs4_mixed_prep profile

   The utf8str_mixed type is a string of UTF-8 characters, with a prefix
   that is case sensitive, a separator equal to '@', and a suffix that
   is fully qualified domain name.  Its primary use in NFS Version 4 is
   for naming principals identified in an Access Control Entry.

11.3.2.  Character repertoire of nfs4_mixed_prep

   The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1

11.3.3.  Mapping used by nfs4_cis_prep

   For the prefix and the separator of a utf8str_mixed string, the
   nfs4_mixed_prep profile specifies mapping using the following table
   from stringprep:

      Table B.1

   For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
   specifies mapping using the following tables from stringprep:




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      Table B.1
      Table B.2

11.3.4.  Normalization used by nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies using Unicode normalization
   form KC, as described in stringprep.

11.3.5.  Prohibited output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2
      Table C.2.2
      Table C.3
      Table C.4
      Table C.5
      Table C.6
      Table C.7
      Table C.8
      Table C.9

11.3.6.  Bidirectional output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies checking bidirectional strings
   as described in stringprep's section 6.

11.4.  UTF-8 Related Errors

   Where the client sends an invalid UTF-8 string, the server should
   return an NFS4ERR_INVAL error.  This includes cases in which
   inappropriate prefixes are detected and where the count includes
   trailing bytes that do not constitute a full UCS character.

   Where the client supplied string is valid UTF-8 but contains
   characters that are not supported by the server as a value for that
   string (e.g., names containing characters that have more than two
   octets on a filesystem that supports Unicode characters only), the
   server should return an NFS4ERR_BADCHAR error.

   Where a UTF-8 string is used as a file name, and the filesystem,
   while supporting all of the characters within the name, does not
   allow that particular name to be used, the server should return the
   error NFS4ERR_BADNAME.  This includes situations in which the server
   filesystem imposes a normalization constraint on name strings, but





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   will also include such situations as filesystem prohibitions of "."
   and ".." as file names for certain operations, and other such
   constraints.

12.  Error Definitions

   NFS error numbers are assigned to failed operations within a compound
   request.  A compound request contains a number of NFS operations that
   have their results encoded in sequence in a compound reply.  The
   results of successful operations will consist of an NFS4_OK status
   followed by the encoded results of the operation.  If an NFS
   operation fails, an error status will be entered in the reply and the
   compound request will be terminated.

   A description of each defined error follows:

   NFS4_OK               Indicates the operation completed successfully.


   NFS4ERR_ACCESS        Permission denied. The caller does not have the
                         correct permission to perform the requested
                         operation. Contrast this with NFS4ERR_PERM,
                         which restricts itself to owner or privileged
                         user permission failures.

   NFS4ERR_ATTRNOTSUPP   An attribute specified is not supported by the
                         server.  Does not apply to the GETATTR
                         operation.

   NFS4ERR_ADMIN_REVOKED Due to administrator intervention, the
                         lockowner's record locks, share reservations,
                         and delegations have been revoked by the
                         server.

   NFS4ERR_BADCHAR       A UTF-8 string contains a character which is
                         not supported by the server in the context in
                         which it being used.

   NFS4ERR_BAD_COOKIE    READDIR cookie is stale.

   NFS4ERR_BADHANDLE     Illegal NFS filehandle. The filehandle failed
                         internal consistency checks.

   NFS4ERR_BADNAME       A name string in a request consists of valid
                         UTF-8 characters supported by the server but
                         the name is not supported by the server as a
                         valid name for current operation.




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   NFS4ERR_BADOWNER      An owner, owner_group, or ACL attribute value
                         can not be translated to local representation.

   NFS4ERR_BADTYPE       An attempt was made to create an object of a
                         type not supported by the server.

   NFS4ERR_BAD_RANGE     The range for a LOCK, LOCKT, or LOCKU operation
                         is not appropriate to the allowable range of
                         offsets for the server.

   NFS4ERR_BAD_SEQID     The sequence number in a locking request is
                         neither the next expected number or the last
                         number processed.

   NFS4ERR_BAD_STATEID   A stateid generated by the current server
                         instance, but which does not designate any
                         locking state (either current or superseded)
                         for a current lockowner-file pair, was used.

   NFS4ERR_BADXDR        The server encountered an XDR decoding error
                         while processing an operation.

   NFS4ERR_CLID_INUSE    The SETCLIENTID operation has found that a
                         client id is already in use by another client.

   NFS4ERR_DEADLOCK      The server has been able to determine a file
                         locking deadlock condition for a blocking lock
                         request.

   NFS4ERR_DELAY         The server initiated the request, but was not
                         able to complete it in a timely fashion. The
                         client should wait and then try the request
                         with a new RPC transaction ID.  For example,
                         this error should be returned from a server
                         that supports hierarchical storage and receives
                         a request to process a file that has been
                         migrated. In this case, the server should start
                         the immigration process and respond to client
                         with this error.  This error may also occur
                         when a necessary delegation recall makes
                         processing a request in a timely fashion
                         impossible.

   NFS4ERR_DENIED        An attempt to lock a file is denied.  Since
                         this may be a temporary condition, the client
                         is encouraged to retry the lock request until
                         the lock is accepted.




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   NFS4ERR_DQUOT         Resource (quota) hard limit exceeded. The
                         user's resource limit on the server has been
                         exceeded.

   NFS4ERR_EXIST         File exists. The file specified already exists.

   NFS4ERR_EXPIRED       A lease has expired that is being used in the
                         current operation.

   NFS4ERR_FBIG          File too large. The operation would have caused
                         a file to grow beyond the server's limit.

   NFS4ERR_FHEXPIRED     The filehandle provided is volatile and has
                         expired at the server.

   NFS4ERR_FILE_OPEN     The operation can not be successfully processed
                         because a file involved in the operation is
                         currently open.

   NFS4ERR_GRACE         The server is in its recovery or grace period
                         which should match the lease period of the
                         server.

   NFS4ERR_INVAL         Invalid argument or unsupported argument for an
                         operation. Two examples are attempting a
                         READLINK on an object other than a symbolic
                         link or specifying a value for an enum field
                         that is not defined in the protocol (e.g.,
                         nfs_ftype4).

   NFS4ERR_IO            I/O error. A hard error (for example, a disk
                         error) occurred while processing the requested
                         operation.

   NFS4ERR_ISDIR         Is a directory. The caller specified a
                         directory in a non-directory operation.

   NFS4ERR_LEASE_MOVED   A lease being renewed is associated with a
                         filesystem that has been migrated to a new
                         server.

   NFS4ERR_LOCKED        A read or write operation was attempted on a
                         locked file.

   NFS4ERR_LOCK_NOTSUPP  Server does not support atomic upgrade or
                         downgrade of locks.





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   NFS4ERR_LOCK_RANGE    A lock request is operating on a sub-range of a
                         current lock for the lock owner and the server
                         does not support this type of request.

   NFS4ERR_LOCKS_HELD    A CLOSE was attempted and file locks would
                         exist after the CLOSE.

   NFS4ERR_MINOR_VERS_MISMATCH
                         The server has received a request that
                         specifies an unsupported minor version.  The
                         server must return a COMPOUND4res with a zero
                         length operations result array.

   NFS4ERR_MLINK         Too many hard links.

   NFS4ERR_MOVED         The filesystem which contains the current
                         filehandle object has been relocated or
                         migrated to another server.  The client may
                         obtain the new filesystem location by obtaining
                         the "fs_locations" attribute for the current
                         filehandle.  For further discussion, refer to
                         the section "Filesystem Migration or
                         Relocation".

   NFS4ERR_NAMETOOLONG   The filename in an operation was too long.

   NFS4ERR_NOENT         No such file or directory. The file or
                         directory name specified does not exist.

   NFS4ERR_NOFILEHANDLE  The logical current filehandle value (or, in
                         the case of RESTOREFH, the saved filehandle
                         value) has not been set properly.  This may be
                         a result of a malformed COMPOUND operation
                         (i.e., no PUTFH or PUTROOTFH before an
                         operation that requires the current filehandle
                         be set).

   NFS4ERR_NO_GRACE      A reclaim of client state has fallen outside of
                         the grace period of the server.  As a result,
                         the server can not guarantee that conflicting
                         state has not been provided to another client.

   NFS4ERR_NOSPC         No space left on device. The operation would
                         have caused the server's filesystem to exceed
                         its limit.

   NFS4ERR_NOTDIR        Not a directory. The caller specified a non-
                         directory in a directory operation.



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   NFS4ERR_NOTEMPTY      An attempt was made to remove a directory that
                         was not empty.

   NFS4ERR_NOTSUPP       Operation is not supported.

   NFS4ERR_NOT_SAME      This error is returned by the VERIFY operation
                         to signify that the attributes compared were
                         not the same as provided in the client's
                         request.

   NFS4ERR_NXIO          I/O error. No such device or address.

   NFS4ERR_OLD_STATEID   A stateid which designates the locking state
                         for a lockowner-file at an earlier time was
                         used.

   NFS4ERR_OPENMODE      The client attempted a READ, WRITE, LOCK or
                         SETATTR operation not sanctioned by the stateid
                         passed (e.g., writing to a file opened only for
                         read).

   NFS4ERR_OP_ILLEGAL    An illegal operation value has been specified
                         in the argop field of a COMPOUND or CB_COMPOUND
                         procedure.

   NFS4ERR_PERM          Not owner. The operation was not allowed
                         because the caller is either not a privileged
                         user (root) or not the owner of the target of
                         the operation.

   NFS4ERR_RECLAIM_BAD   The reclaim provided by the client does not
                         match any of the server's state consistency
                         checks and is bad.

   NFS4ERR_RECLAIM_CONFLICT
                         The reclaim provided by the client has
                         encountered a conflict and can not be provided.
                         Potentially indicates a misbehaving client.

   NFS4ERR_RESOURCE      For the processing of the COMPOUND procedure,
                         the server may exhaust available resources and
                         can not continue processing operations within
                         the COMPOUND procedure.  This error will be
                         returned from the server in those instances of
                         resource exhaustion related to the processing
                         of the COMPOUND procedure.





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   NFS4ERR_RESTOREFH     The RESTOREFH operation does not have a saved
                         filehandle (identified by SAVEFH) to operate
                         upon.

   NFS4ERR_ROFS          Read-only filesystem. A modifying operation was
                         attempted on a read-only filesystem.

   NFS4ERR_SAME          This error is returned by the NVERIFY operation
                         to signify that the attributes compared were
                         the same as provided in the client's request.

   NFS4ERR_SERVERFAULT   An error occurred on the server which does not
                         map to any of the legal NFS version 4 protocol
                         error values.  The client should translate this
                         into an appropriate error.  UNIX clients may
                         choose to translate this to EIO.

   NFS4ERR_SHARE_DENIED  An attempt to OPEN a file with a share
                         reservation has failed because of a share
                         conflict.

   NFS4ERR_STALE         Invalid filehandle. The filehandle given in the
                         arguments was invalid. The file referred to by
                         that filehandle no longer exists or access to
                         it has been revoked.

   NFS4ERR_STALE_CLIENTID A clientid not recognized by the server was
                          used in a locking or SETCLIENTID_CONFIRM
                          request.

   NFS4ERR_STALE_STATEID A stateid generated by an earlier server
                         instance was used.

   NFS4ERR_SYMLINK       The current filehandle provided for a LOOKUP is
                         not a directory but a symbolic link.  Also used
                         if the final component of the OPEN path is a
                         symbolic link.

   NFS4ERR_TOOSMALL      The encoded response to a READDIR request
                         exceeds the size limit set by the initial
                         request.

   NFS4ERR_WRONGSEC      The security mechanism being used by the client
                         for the operation does not match the server's
                         security policy.  The client should change the
                         security mechanism being used and retry the
                         operation.




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   NFS4ERR_XDEV          Attempt to do an operation between different
                         fsids.

13.  NFS version 4 Requests

   For the NFS version 4 RPC program, there are two traditional RPC
   procedures: NULL and COMPOUND.  All other functionality is defined as
   a set of operations and these operations are defined in normal
   XDR/RPC syntax and semantics.  However, these operations are
   encapsulated within the COMPOUND procedure.  This requires that the
   client combine one or more of the NFS version 4 operations into a
   single request.

   The NFS4_CALLBACK program is used to provide server to client
   signaling and is constructed in a similar fashion as the NFS version
   4 program.  The procedures CB_NULL and CB_COMPOUND are defined in the
   same way as NULL and COMPOUND are within the NFS program.  The
   CB_COMPOUND request also encapsulates the remaining operations of the
   NFS4_CALLBACK program.  There is no predefined RPC program number for
   the NFS4_CALLBACK program.  It is up to the client to specify a
   program number in the "transient" program range.  The program and
   port number of the NFS4_CALLBACK program are provided by the client
   as part of the SETCLIENTID/SETCLIENTID_CONFIRM sequence. The program
   and port can be changed by another SETCLIENTID/SETCLIENTID_CONFIRM
   sequence, and it is possible to use the sequence to change them
   within a client incarnation without removing relevant leased client
   state.

13.1.  Compound Procedure

   The COMPOUND procedure provides the opportunity for better
   performance within high latency networks.  The client can avoid
   cumulative latency of multiple RPCs by combining multiple dependent
   operations into a single COMPOUND procedure.  A compound operation
   may provide for protocol simplification by allowing the client to
   combine basic procedures into a single request that is customized for
   the client's environment.

   The CB_COMPOUND procedure precisely parallels the features of
   COMPOUND as described above.

   The basic structure of the COMPOUND procedure is:

   +-----+--------------+--------+-----------+-----------+-----------+--
   | tag | minorversion | numops | op + args | op + args | op + args |
   +-----+--------------+--------+-----------+-----------+-----------+--





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   and the reply's structure is:

      +------------+-----+--------+-----------------------+--
      |last status | tag | numres | status + op + results |
      +------------+-----+--------+-----------------------+--

   The numops and numres fields, used in the depiction above, represent
   the count for the counted array encoding use to signify the number of
   arguments or results encoded in the request and response.  As per the
   XDR encoding, these counts must match exactly the number of operation
   arguments or results encoded.

13.2.  Evaluation of a Compound Request

   The server will process the COMPOUND procedure by evaluating each of
   the operations within the COMPOUND procedure in order.  Each
   component operation consists of a 32 bit operation code, followed by
   the argument of length determined by the type of operation. The
   results of each operation are encoded in sequence into a reply
   buffer.  The results of each operation are preceded by the opcode and
   a status code (normally zero).  If an operation results in a non-zero
   status code, the status will be encoded and evaluation of the
   compound sequence will halt and the reply will be returned.  Note
   that evaluation stops even in the event of "non error" conditions
   such as NFS4ERR_SAME.

   There are no atomicity requirements for the operations contained
   within the COMPOUND procedure.  The operations being evaluated as
   part of a COMPOUND request may be evaluated simultaneously with other
   COMPOUND requests that the server receives.

   It is the client's responsibility for recovering from any partially
   completed COMPOUND procedure.  Partially completed COMPOUND
   procedures may occur at any point due to errors such as
   NFS4ERR_RESOURCE and NFS4ERR_DELAY.  This may occur even given an
   otherwise valid operation string.  Further, a server reboot which
   occurs in the middle of processing a COMPOUND procedure may leave the
   client with the difficult task of determining how far COMPOUND
   processing has proceeded.  Therefore, the client should avoid overly
   complex COMPOUND procedures in the event of the failure of an
   operation within the procedure.

   Each operation assumes a "current" and "saved" filehandle that is
   available as part of the execution context of the compound request.
   Operations may set, change, or return the current filehandle.  The
   "saved" filehandle is used for temporary storage of a filehandle
   value and as operands for the RENAME and LINK operations.




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13.3.  Synchronous Modifying Operations

   NFS version 4 operations that modify the filesystem are synchronous.
   When an operation is successfully completed at the server, the client
   can depend that any data associated with the request is now on stable
   storage (the one exception is in the case of the file data in a WRITE
   operation with the UNSTABLE option specified).

   This implies that any previous operations within the same compound
   request are also reflected in stable storage.  This behavior enables
   the client's ability to recover from a partially executed compound
   request which may resulted from the failure of the server.  For
   example, if a compound request contains operations A and B and the
   server is unable to send a response to the client, depending on the
   progress the server made in servicing the request the result of both
   operations may be reflected in stable storage or just operation A may
   be reflected.  The server must not have just the results of operation
   B in stable storage.

13.4.  Operation Values

   The operations encoded in the COMPOUND procedure are identified by
   operation values.  To avoid overlap with the RPC procedure numbers,
   operations 0 (zero) and 1 are not defined.  Operation 2 is not
   defined but reserved for future use with minor versioning.

14.  NFS version 4 Procedures

14.1.  Procedure 0: NULL - No Operation

   SYNOPSIS

      <null>

   ARGUMENT

      void;

   RESULT

      void;










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   DESCRIPTION

      Standard NULL procedure.  Void argument, void response.  This
      procedure has no functionality associated with it.  Because of
      this it is sometimes used to measure the overhead of processing a
      service request.  Therefore, the server should ensure that no
      unnecessary work is done in servicing this procedure.

   ERRORS

      None.

14.2.  Procedure 1: COMPOUND - Compound Operations

   SYNOPSIS

     compoundargs -> compoundres

   ARGUMENT

     union nfs_argop4 switch (nfs_opnum4 argop) {
             case <OPCODE>: <argument>;
             ...
     };

     struct COMPOUND4args {
             utf8str_cs      tag;
             uint32_t        minorversion;
             nfs_argop4      argarray<>;
     };

   RESULT

     union nfs_resop4 switch (nfs_opnum4 resop){
             case <OPCODE>: <result>;
             ...
     };

     struct COMPOUND4res {
             nfsstat4        status;
             utf8str_cs      tag;
             nfs_resop4      resarray<>;
     };








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   DESCRIPTION

   The COMPOUND procedure is used to combine one or more of the NFS
   operations into a single RPC request.  The main NFS RPC program has
   two main procedures: NULL and COMPOUND.  All other operations use the
   COMPOUND procedure as a wrapper.

   The COMPOUND procedure is used to combine individual operations into
   a single RPC request.  The server interprets each of the operations
   in turn.  If an operation is executed by the server and the status of
   that operation is NFS4_OK, then the next operation in the COMPOUND
   procedure is executed.  The server continues this process until there
   are no more operations to be executed or one of the operations has a
   status value other than NFS4_OK.

   In the processing of the COMPOUND procedure, the server may find that
   it does not have the available resources to execute any or all of the
   operations within the COMPOUND sequence.  In this case, the error
   NFS4ERR_RESOURCE will be returned for the particular operation within
   the COMPOUND procedure where the resource exhaustion occurred.  This
   assumes that all previous operations within the COMPOUND sequence
   have been evaluated successfully.  The results for all of the
   evaluated operations must be returned to the client.

   The server will generally choose between two methods of decoding the
   client's request.  The first would be the traditional one-pass XDR
   decode, in which decoding of the entire COMPOUND precedes execution
   of any operation within it.  If there is an XDR decoding error in
   this case, an RPC XDR decode error would be returned.  The second
   method would be to make an initial pass to decode the basic COMPOUND
   request and then to XDR decode each of the individual operations, as
   the server is ready to execute it.  In this case, the server may
   encounter an XDR decode error during such an operation decode, after
   previous operations within the COMPOUND have been executed.  In this
   case, the server would return the error NFS4ERR_BADXDR to signify the
   decode error.

   The COMPOUND arguments contain a "minorversion" field.  The initial
   and default value for this field is 0 (zero).  This field will be
   used by future minor versions such that the client can communicate to
   the server what minor version is being requested.  If the server
   receives a COMPOUND procedure with a minorversion field value that it
   does not support, the server MUST return an error of
   NFS4ERR_MINOR_VERS_MISMATCH and a zero length resultdata array.

   Contained within the COMPOUND results is a "status" field.  If the
   results array length is non-zero, this status must be equivalent to
   the status of the last operation that was executed within the



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   COMPOUND procedure.  Therefore, if an operation incurred an error
   then the "status" value will be the same error value as is being
   returned for the operation that failed.

   Note that operations, 0 (zero) and 1 (one) are not defined for the
   COMPOUND procedure.  Operation 2 is not defined but reserved for
   future definition and use with minor versioning.  If the server
   receives a operation array that contains operation 2 and the
   minorversion field has a value of 0 (zero), an error of
   NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned
   to the client.  If an operation array contains an operation 2 and the
   minorversion field is non-zero and the server does not support the
   minor version, the server returns an error of
   NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
   NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
   errors.

   It is possible that the server receives a request that contains an
   operation that is less than the first legal operation (OP_ACCESS) or
   greater than the last legal operation (OP_RELEASE_LOCKOWNER).

   In this case, the server's response will encode the opcode OP_ILLEGAL
   rather than the illegal opcode of the request. The status field in
   the ILLEGAL return results will set to NFS4ERR_OP_ILLEGAL.  The
   COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.

   The definition of the "tag" in the request is left to the
   implementor.  It may be used to summarize the content of the compound
   request for the benefit of packet sniffers and engineers debugging
   implementations.  However, the value of "tag" in the response SHOULD
   be the same value as provided in the request.  This applies to the
   tag field of the CB_COMPOUND procedure as well.

   IMPLEMENTATION

   Since an error of any type may occur after only a portion of the
   operations have been evaluated, the client must be prepared to
   recover from any failure.  If the source of an NFS4ERR_RESOURCE error
   was a complex or lengthy set of operations, it is likely that if the
   number of operations were reduced the server would be able to
   evaluate them successfully.  Therefore, the client is responsible for
   dealing with this type of complexity in recovery.

   ERRORS

   All errors defined in the protocol





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14.2.1.  Operation 3: ACCESS - Check Access Rights

   SYNOPSIS

     (cfh), accessreq -> supported, accessrights

   ARGUMENT

     const ACCESS4_READ      = 0x00000001;
     const ACCESS4_LOOKUP    = 0x00000002;
     const ACCESS4_MODIFY    = 0x00000004;
     const ACCESS4_EXTEND    = 0x00000008;
     const ACCESS4_DELETE    = 0x00000010;
     const ACCESS4_EXECUTE   = 0x00000020;

     struct ACCESS4args {
             /* CURRENT_FH: object */
             uint32_t        access;
     };

   RESULT

     struct ACCESS4resok {
             uint32_t        supported;
             uint32_t        access;
     };

     union ACCESS4res switch (nfsstat4 status) {
      case NFS4_OK:
              ACCESS4resok   resok4;
      default:
              void;
     };

   DESCRIPTION

   ACCESS determines the access rights that a user, as identified by the
   credentials in the RPC request, has with respect to the file system
   object specified by the current filehandle.  The client encodes the
   set of access rights that are to be checked in the bit mask "access".
   The server checks the permissions encoded in the bit mask.  If a
   status of NFS4_OK is returned, two bit masks are included in the
   response.  The first, "supported", represents the access rights for
   which the server can verify reliably.  The second, "access",
   represents the access rights available to the user for the filehandle
   provided.  On success, the current filehandle retains its value.





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   Note that the supported field will contain only as many values as
   were originally sent in the arguments.  For example, if the client
   sends an ACCESS operation with only the ACCESS4_READ value set and
   the server supports this value, the server will return only
   ACCESS4_READ even if it could have reliably checked other values.

   The results of this operation are necessarily advisory in nature.  A
   return status of NFS4_OK and the appropriate bit set in the bit mask
   does not imply that such access will be allowed to the file system
   object in the future. This is because access rights can be revoked by
   the server at any time.

   The following access permissions may be requested:

   ACCESS4_READ    Read data from file or read a directory.

   ACCESS4_LOOKUP  Look up a name in a directory (no meaning for non-
                   directory objects).

   ACCESS4_MODIFY  Rewrite existing file data or modify existing
                   directory entries.

   ACCESS4_EXTEND  Write new data or add directory entries.

   ACCESS4_DELETE  Delete an existing directory entry.

   ACCESS4_EXECUTE Execute file (no meaning for a directory).

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   In general, it is not sufficient for the client to attempt to deduce
   access permissions by inspecting the uid, gid, and mode fields in the
   file attributes or by attempting to interpret the contents of the ACL
   attribute.  This is because the server may perform uid or gid mapping
   or enforce additional access control restrictions.  It is also
   possible that the server may not be in the same ID space as the
   client.  In these cases (and perhaps others), the client can not
   reliably perform an access check with only current file attributes.

   In the NFS version 2 protocol, the only reliable way to determine
   whether an operation was allowed was to try it and see if it
   succeeded or failed.  Using the ACCESS operation in the NFS version 4
   protocol, the client can ask the server to indicate whether or not
   one or more classes of operations are permitted.  The ACCESS
   operation is provided to allow clients to check before doing a series
   of operations which will result in an access failure.  The OPEN



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   operation provides a point where the server can verify access to the
   file object and method to return that information to the client.  The
   ACCESS operation is still useful for directory operations or for use
   in the case the UNIX API "access" is used on the client.

   The information returned by the server in response to an ACCESS call
   is not permanent.  It was correct at the exact time that the server
   performed the checks, but not necessarily afterwards.  The server can
   revoke access permission at any time.

   The client should use the effective credentials of the user to build
   the authentication information in the ACCESS request used to
   determine access rights.  It is the effective user and group
   credentials that are used in subsequent read and write operations.

   Many implementations do not directly support the ACCESS4_DELETE
   permission.  Operating systems like UNIX will ignore the
   ACCESS4_DELETE bit if set on an access request on a non-directory
   object.  In these systems, delete permission on a file is determined
   by the access permissions on the directory in which the file resides,
   instead of being determined by the permissions of the file itself.
   Therefore, the mask returned enumerating which access rights can be
   determined will have the ACCESS4_DELETE value set to 0.  This
   indicates to the client that the server was unable to check that
   particular access right.  The ACCESS4_DELETE bit in the access mask
   returned will then be ignored by the client.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.2.  Operation 4: CLOSE - Close File

   SYNOPSIS

     (cfh), seqid, open_stateid -> open_stateid




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   ARGUMENT

     struct CLOSE4args {
             /* CURRENT_FH: object */
             seqid4          seqid
             stateid4        open_stateid;
     };

   RESULT

     union CLOSE4res switch (nfsstat4 status) {
      case NFS4_OK:
              stateid4       open_stateid;
      default:
              void;
     };

   DESCRIPTION

   The CLOSE operation releases share reservations for the regular or
   named attribute file as specified by the current filehandle.  The
   share reservations and other state information released at the server
   as a result of this CLOSE is only associated with the supplied
   stateid.  The sequence id provides for the correct ordering. State
   associated with other OPENs is not affected.

   If record locks are held, the client SHOULD release all locks before
   issuing a CLOSE.  The server MAY free all outstanding locks on CLOSE
   but some servers may not support the CLOSE of a file that still has
   record locks held.  The server MUST return failure if any locks would
   exist after the CLOSE.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   Even though CLOSE returns a stateid, this stateid is not useful to
   the client and should be treated as deprecated.  CLOSE "shuts down"
   the state associated with all OPENs for the file by a single
   open_owner.  As noted above, CLOSE will either release all file
   locking state or return an error.  Therefore, the stateid returned by
   CLOSE is not useful for operations that follow.

   ERRORS

      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_SEQID



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      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_EXPIRED
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCKS_HELD
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_OLD_STATEID
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID

14.2.3.  Operation 5: COMMIT - Commit Cached Data

   SYNOPSIS

     (cfh), offset, count -> verifier

   ARGUMENT

     struct COMMIT4args {
             /* CURRENT_FH: file */
             offset4         offset;
             count4          count;
     };

   RESULT

     struct COMMIT4resok {
             verifier4       writeverf;
     };

     union COMMIT4res switch (nfsstat4 status) {
      case NFS4_OK:
              COMMIT4resok   resok4;
      default:
              void;
     };








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   DESCRIPTION

   The COMMIT operation forces or flushes data to stable storage for the
   file specified by the current filehandle.  The flushed data is that
   which was previously written with a WRITE operation which had the
   stable field set to UNSTABLE4.

   The offset specifies the position within the file where the flush is
   to begin.  An offset value of 0 (zero) means to flush data starting
   at the beginning of the file.  The count specifies the number of
   bytes of data to flush.  If count is 0 (zero), a flush from offset to
   the end of the file is done.

   The server returns a write verifier upon successful completion of the
   COMMIT.  The write verifier is used by the client to determine if the
   server has restarted or rebooted between the initial WRITE(s) and the
   COMMIT.  The client does this by comparing the write verifier
   returned from the initial writes and the verifier returned by the
   COMMIT operation.  The server must vary the value of the write
   verifier at each server event or instantiation that may lead to a
   loss of uncommitted data.  Most commonly this occurs when the server
   is rebooted; however, other events at the server may result in
   uncommitted data loss as well.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   The COMMIT operation is similar in operation and semantics to the
   POSIX fsync(2) system call that synchronizes a file's state with the
   disk (file data and metadata is flushed to disk or stable storage).
   COMMIT performs the same operation for a client, flushing any
   unsynchronized data and metadata on the server to the server's disk
   or stable storage for the specified file.  Like fsync(2), it may be
   that there is some modified data or no modified data to synchronize.
   The data may have been synchronized by the server's normal periodic
   buffer synchronization activity.  COMMIT should return NFS4_OK,
   unless there has been an unexpected error.

   COMMIT differs from fsync(2) in that it is possible for the client to
   flush a range of the file (most likely triggered by a buffer-
   reclamation scheme on the client before file has been completely
   written).

   The server implementation of COMMIT is reasonably simple.  If the
   server receives a full file COMMIT request, that is starting at
   offset 0 and count 0, it should do the equivalent of fsync()'ing the
   file.  Otherwise, it should arrange to have the cached data in the



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   range specified by offset and count to be flushed to stable storage.
   In both cases, any metadata associated with the file must be flushed
   to stable storage before returning.  It is not an error for there to
   be nothing to flush on the server.  This means that the data and
   metadata that needed to be flushed have already been flushed or lost
   during the last server failure.

   The client implementation of COMMIT is a little more complex.  There
   are two reasons for wanting to commit a client buffer to stable
   storage.  The first is that the client wants to reuse a buffer.  In
   this case, the offset and count of the buffer are sent to the server
   in the COMMIT request.  The server then flushes any cached data based
   on the offset and count, and flushes any metadata associated with the
   file.  It then returns the status of the flush and the write
   verifier.  The other reason for the client to generate a COMMIT is
   for a full file flush, such as may be done at close.  In this case,
   the client would gather all of the buffers for this file that contain
   uncommitted data, do the COMMIT operation with an offset of 0 and
   count of 0, and then free all of those buffers.  Any other dirty
   buffers would be sent to the server in the normal fashion.

   After a buffer is written by the client with the stable parameter set
   to UNSTABLE4, the buffer must be considered as modified by the client
   until the buffer has either been flushed via a COMMIT operation or
   written via a WRITE operation with stable parameter set to FILE_SYNC4
   or DATA_SYNC4. This is done to prevent the buffer from being freed
   and reused before the data can be flushed to stable storage on the
   server.

   When a response is returned from either a WRITE or a COMMIT operation
   and it contains a write verifier that is different than previously
   returned by the server, the client will need to retransmit all of the
   buffers containing uncommitted cached data to the server.  How this
   is to be done is up to the implementor.  If there is only one buffer
   of interest, then it should probably be sent back over in a WRITE
   request with the appropriate stable parameter.  If there is more than
   one buffer, it might be worthwhile retransmitting all of the buffers
   in WRITE requests with the stable parameter set to UNSTABLE4 and then
   retransmitting the COMMIT operation to flush all of the data on the
   server to stable storage.  The timing of these retransmissions is
   left to the implementor.

   The above description applies to page-cache-based systems as well as
   buffer-cache-based systems.  In those systems, the virtual memory
   system will need to be modified instead of the buffer cache.






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   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_ISDIR
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.4.  Operation 6: CREATE - Create a Non-Regular File Object

   SYNOPSIS

     (cfh), name, type, attrs -> (cfh), change_info, attrs_set

   ARGUMENT

     union createtype4 switch (nfs_ftype4 type) {
      case NF4LNK:
              linktext4      linkdata;
      case NF4BLK:
      case NF4CHR:
              specdata4      devdata;
      case NF4SOCK:
      case NF4FIFO:
      case NF4DIR:
              void;
     };

     struct CREATE4args {
             /* CURRENT_FH: directory for creation */
             createtype4     objtype;
             component4      objname;
             fattr4          createattrs;
     };

   RESULT

     struct CREATE4resok {
             change_info4    cinfo;
             bitmap4         attrset;        /* attributes set */



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     };

     union CREATE4res switch (nfsstat4 status) {
      case NFS4_OK:
              CREATE4resok resok4;
      default:
              void;
     };

   DESCRIPTION

   The CREATE operation creates a non-regular file object in a directory
   with a given name.  The OPEN operation MUST be used to create a
   regular file.

   The objname specifies the name for the new object.  The objtype
   determines the type of object to be created: directory, symlink, etc.

   If an object of the same name already exists in the directory, the
   server will return the error NFS4ERR_EXIST.

   For the directory where the new file object was created, the server
   returns change_info4 information in cinfo.  With the atomic field of
   the change_info4 struct, the server will indicate if the before and
   after change attributes were obtained atomically with respect to the
   file object creation.

   If the objname has a length of 0 (zero), or if objname does not obey
   the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   The current filehandle is replaced by that of the new object.

   The createattrs specifies the initial set of attributes for the
   object.  The set of attributes may include any writable attribute
   valid for the object type. When the operation is successful, the
   server will return to the client an attribute mask signifying which
   attributes were successfully set for the object.

   If createattrs includes neither the owner attribute nor an ACL with
   an ACE for the owner, and if the server's filesystem both supports
   and requires an owner attribute (or an owner ACE) then the server
   MUST derive the owner (or the owner ACE). This would typically be
   from the principal indicated in the RPC credentials of the call, but
   the server's operating environment or filesystem semantics may
   dictate other methods of derivation. Similarly, if createattrs
   includes neither the group attribute nor a group ACE, and if the
   server's filesystem both supports and requires the notion of a group
   attribute (or group ACE), the server MUST derive the group attribute



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   (or the corresponding owner ACE) for the file. This could be from the
   RPC call's credentials, such as the group principal if the
   credentials include it (such as with AUTH_SYS), from the group
   identifier associated with the principal in the credentials (for
   e.g., POSIX systems have a passwd database that has the group
   identifier for every user identifier), inherited from directory the
   object is created in, or whatever else the server's operating
   environment or filesystem semantics dictate. This applies to the OPEN
   operation too.

   Conversely, it is possible the client will specify in createattrs an
   owner attribute or group attribute or ACL that the principal
   indicated the RPC call's credentials does not have permissions to
   create files for. The error to be returned in this instance is
   NFS4ERR_PERM. This applies to the OPEN operation too.

   IMPLEMENTATION

   If the client desires to set attribute values after the create, a
   SETATTR operation can be added to the COMPOUND request so that the
   appropriate attributes will be set.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ATTRNOTSUPP
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADOWNER
      NFS4ERR_BADTYPE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_EXIST
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_NOTDIR
      NFS4ERR_PERM
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE



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14.2.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery

   SYNOPSIS

     clientid ->

   ARGUMENT

     struct DELEGPURGE4args {
             clientid4       clientid;
     };

   RESULT

     struct DELEGPURGE4res {
             nfsstat4        status;
     };

   DESCRIPTION

   Purges all of the delegations awaiting recovery for a given client.
   This is useful for clients which do not commit delegation information
   to stable storage to indicate that conflicting requests need not be
   delayed by the server awaiting recovery of delegation information.

   This operation should be used by clients that record delegation
   information on stable storage on the client.  In this case,
   DELEGPURGE should be issued immediately after doing delegation
   recovery on all delegations known to the client.  Doing so will
   notify the server that no additional delegations for the client will
   be recovered allowing it to free resources, and avoid delaying other
   clients who make requests that conflict with the unrecovered
   delegations.  The set of delegations known to the server and the
   client may be different.  The reason for this is that a client may
   fail after making a request which resulted in delegation but before
   it received the results and committed them to the client's stable
   storage.

   The server MAY support DELEGPURGE, but if it does not, it MUST NOT
   support CLAIM_DELEGATE_PREV.

   ERRORS

      NFS4ERR_BADXDR
      NFS4ERR_NOTSUPP
      NFS4ERR_LEASE_MOVED
      NFS4ERR_MOVED
      NFS4ERR_RESOURCE



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      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE_CLIENTID

14.2.6.  Operation 8: DELEGRETURN - Return Delegation

   SYNOPSIS

     (cfh), stateid ->

   ARGUMENT

     struct DELEGRETURN4args {
             /* CURRENT_FH: delegated file */
             stateid4        stateid;
     };

   RESULT

     struct DELEGRETURN4res {
             nfsstat4        status;
     };

   DESCRIPTION

   Returns the delegation represented by the current filehandle and
   stateid.

   Delegations may be returned when recalled or voluntarily (i.e.,
   before the server has recalled them).  In either case the client must
   properly propagate state changed under the context of the delegation
   to the server before returning the delegation.

   ERRORS

      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_EXPIRED
      NFS4ERR_INVAL
      NFS4ERR_LEASE_MOVED
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTSUPP
      NFS4ERR_OLD_STATEID
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID



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14.2.7.  Operation 9: GETATTR - Get Attributes

   SYNOPSIS

     (cfh), attrbits -> attrbits, attrvals

   ARGUMENT

     struct GETATTR4args {
             /* CURRENT_FH: directory or file */
             bitmap4         attr_request;
     };

   RESULT

     struct GETATTR4resok {
             fattr4          obj_attributes;
     };

     union GETATTR4res switch (nfsstat4 status) {
      case NFS4_OK:
              GETATTR4resok  resok4;
      default:
              void;
     };

   DESCRIPTION

   The GETATTR operation will obtain attributes for the filesystem
   object specified by the current filehandle.  The client sets a bit in
   the bitmap argument for each attribute value that it would like the
   server to return.  The server returns an attribute bitmap that
   indicates the attribute values for which it was able to return,
   followed by the attribute values ordered lowest attribute number
   first.

   The server must return a value for each attribute that the client
   requests if the attribute is supported by the server.  If the server
   does not support an attribute or cannot approximate a useful value
   then it must not return the attribute value and must not set the
   attribute bit in the result bitmap.  The server must return an error
   if it supports an attribute but cannot obtain its value.  In that
   case no attribute values will be returned.

   All servers must support the mandatory attributes as specified in the
   section "File Attributes".

   On success, the current filehandle retains its value.



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   IMPLEMENTATION

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.8.  Operation 10: GETFH - Get Current Filehandle

   SYNOPSIS

     (cfh) -> filehandle

   ARGUMENT

     /* CURRENT_FH: */
     void;


   RESULT

     struct GETFH4resok {
             nfs_fh4         object;
     };

     union GETFH4res switch (nfsstat4 status) {
      case NFS4_OK:
             GETFH4resok     resok4;
      default:
             void;
     };

   DESCRIPTION

   This operation returns the current filehandle value.

   On success, the current filehandle retains its value.




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   IMPLEMENTATION

   Operations that change the current filehandle like LOOKUP or CREATE
   do not automatically return the new filehandle as a result.  For
   instance, if a client needs to lookup a directory entry and obtain
   its filehandle then the following request is needed.

      PUTFH  (directory filehandle)
      LOOKUP (entry name)
      GETFH

   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_FHEXPIRED
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.9.  Operation 11: LINK - Create Link to a File

   SYNOPSIS

     (sfh), (cfh), newname -> (cfh), change_info

   ARGUMENT

     struct LINK4args {
             /* SAVED_FH: source object */
             /* CURRENT_FH: target directory */
             component4      newname;
     };

   RESULT

     struct LINK4resok {
             change_info4    cinfo;
     };

     union LINK4res switch (nfsstat4 status) {
      case NFS4_OK:
              LINK4resok resok4;
      default:
              void;
     };




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   DESCRIPTION

   The LINK operation creates an additional newname for the file
   represented by the saved filehandle, as set by the SAVEFH operation,
   in the directory represented by the current filehandle.  The existing
   file and the target directory must reside within the same filesystem
   on the server.  On success, the current filehandle will continue to
   be the target directory.  If an object exists in the target directory
   with the same name as newname, the server must return NFS4ERR_EXIST.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 struct, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   If the newname has a length of 0 (zero), or if newname does not obey
   the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   IMPLEMENTATION

   Changes to any property of the "hard" linked files are reflected in
   all of the linked files.  When a link is made to a file, the
   attributes for the file should have a value for numlinks that is one
   greater than the value before the LINK operation.

   The statement "file and the target directory must reside within the
   same filesystem on the server" means that the fsid fields in the
   attributes for the objects are the same. If they reside on different
   filesystems, the error, NFS4ERR_XDEV, is returned.  On some servers,
   the filenames, "." and "..", are illegal as newname.

   In the case that newname is already linked to the file represented by
   the saved filehandle, the server will return NFS4ERR_EXIST.

   Note that symbolic links are created with the CREATE operation.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_EXIST
      NFS4ERR_FHEXPIRED
      NFS4ERR_FILE_OPEN



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      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_ISDIR
      NFS4ERR_MLINK
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_NOTDIR
      NFS4ERR_NOTSUPP
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_WRONGSEC
      NFS4ERR_XDEV

14.2.10.  Operation 12: LOCK - Create Lock

   SYNOPSIS

     (cfh) locktype, reclaim, offset, length, locker -> stateid

   ARGUMENT

     struct open_to_lock_owner4 {
             seqid4          open_seqid;
             stateid4        open_stateid;
             seqid4          lock_seqid;
             lock_owner4     lock_owner;
     };

     struct exist_lock_owner4 {
             stateid4        lock_stateid;
             seqid4          lock_seqid;
     };

     union locker4 switch (bool new_lock_owner) {
      case TRUE:
             open_to_lock_owner4     open_owner;
      case FALSE:
             exist_lock_owner4       lock_owner;
     };

     enum nfs_lock_type4 {
             READ_LT         = 1,
             WRITE_LT        = 2,



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             READW_LT        = 3,    /* blocking read */
             WRITEW_LT       = 4     /* blocking write */
     };

     struct LOCK4args {
             /* CURRENT_FH: file */
             nfs_lock_type4  locktype;
             bool            reclaim;
             offset4         offset;
             length4         length;
             locker4         locker;
     };

   RESULT

     struct LOCK4denied {
             offset4         offset;
             length4         length;
             nfs_lock_type4  locktype;
             lock_owner4     owner;
     };

     struct LOCK4resok {
             stateid4        lock_stateid;
     };

     union LOCK4res switch (nfsstat4 status) {
      case NFS4_OK:
              LOCK4resok     resok4;
      case NFS4ERR_DENIED:
              LOCK4denied    denied;
      default:
              void;
     };

   DESCRIPTION

   The LOCK operation requests a record lock for the byte range
   specified by the offset and length parameters.  The lock type is also
   specified to be one of the nfs_lock_type4s.  If this is a reclaim
   request, the reclaim parameter will be TRUE;

   Bytes in a file may be locked even if those bytes are not currently
   allocated to the file.  To lock the file from a specific offset
   through the end-of-file (no matter how long the file actually is) use
   a length field with all bits set to 1 (one).  If the length is zero,





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   or if a length which is not all bits set to one is specified, and
   length when added to the offset exceeds the maximum 64-bit unsigned
   integer value, the error NFS4ERR_INVAL will result.

   Some servers may only support locking for byte offsets that fit
   within 32 bits.  If the client specifies a range that includes a byte
   beyond the last byte offset of the 32-bit range, but does not include
   the last byte offset of the 32-bit and all of the byte offsets beyond
   it, up to the end of the valid 64-bit range, such a 32-bit server
   MUST return the error NFS4ERR_BAD_RANGE.

   In the case that the lock is denied, the owner, offset, and length of
   a conflicting lock are returned.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting lock, the same offset and length that were provided
   in the arguments should be returned in the denied results.  The File
   Locking section contains a full description of this and the other
   file locking operations.

   LOCK operations are subject to permission checks and to checks
   against the access type of the associated file.  However, the
   specific right and modes required for various type of locks, reflect
   the semantics of the server-exported filesystem, and are not
   specified by the protocol.  For example, Windows 2000 allows a write
   lock of a file open for READ, while a POSIX-compliant system does
   not.

   When the client makes a lock request that corresponds to a range that
   the lockowner has locked already (with the same or different lock
   type), or to a sub-region of such a range, or to a region which
   includes multiple locks already granted to that lockowner, in whole
   or in part, and the server does not support such locking operations
   (i.e., does not support POSIX locking semantics), the server will
   return the error NFS4ERR_LOCK_RANGE.  In that case, the client may
   return an error, or it may emulate the required operations, using
   only LOCK for ranges that do not include any bytes already locked by
   that lock_owner and LOCKU of locks held by that lock_owner
   (specifying an exactly-matching range and type).  Similarly, when the
   client makes a lock request that amounts to upgrading (changing from
   a read lock to a write lock) or downgrading (changing from write lock
   to a read lock) an existing record lock, and the server does not





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   support such a lock, the server will return NFS4ERR_LOCK_NOTSUPP.
   Such operations may not perfectly reflect the required semantics in
   the face of conflicting lock requests from other clients.

   The locker argument specifies the lock_owner that is associated with
   the LOCK request.  The locker4 structure is a switched union that
   indicates whether the lock_owner is known to the server or if the
   lock_owner is new to the server.  In the case that the lock_owner is
   known to the server and has an established lock_seqid, the argument
   is just the lock_owner and lock_seqid.  In the case that the
   lock_owner is not known to the server, the argument contains not only
   the lock_owner and lock_seqid but also the open_stateid and
   open_seqid.  The new lock_owner case covers the very first lock done
   by the lock_owner and offers a method to use the established state of
   the open_stateid to transition to the use of the lock_owner.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_RANGE
      NFS4ERR_BAD_SEQID
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_DEADLOCK
      NFS4ERR_DELAY
      NFS4ERR_DENIED
      NFS4ERR_EXPIRED
      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCK_NOTSUPP
      NFS4ERR_LOCK_RANGE
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NO_GRACE
      NFS4ERR_OLD_STATEID
      NFS4ERR_OPENMODE
      NFS4ERR_RECLAIM_BAD
      NFS4ERR_RECLAIM_CONFLICT
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_CLIENTID
      NFS4ERR_STALE_STATEID



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14.2.11.  Operation 13: LOCKT - Test For Lock

   SYNOPSIS

     (cfh) locktype, offset, length owner -> {void, NFS4ERR_DENIED ->
     owner}

   ARGUMENT

     struct LOCKT4args {
             /* CURRENT_FH: file */
             nfs_lock_type4  locktype;
             offset4         offset;
             length4         length;
             lock_owner4     owner;
     };

   RESULT

     struct LOCK4denied {
             offset4         offset;
             length4         length;
             nfs_lock_type4  locktype;
             lock_owner4     owner;
     };

     union LOCKT4res switch (nfsstat4 status) {
      case NFS4ERR_DENIED:
              LOCK4denied    denied;
      case NFS4_OK:
              void;
      default:
              void;
     };

   DESCRIPTION

   The LOCKT operation tests the lock as specified in the arguments.  If
   a conflicting lock exists, the owner, offset, length, and type of the
   conflicting lock are returned; if no lock is held, nothing other than
   NFS4_OK is returned.  Lock types READ_LT and READW_LT are processed
   in the same way in that a conflicting lock test is done without
   regard to blocking or non-blocking.  The same is true for WRITE_LT
   and WRITEW_LT.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.



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   On success, the current filehandle retains its value.

   IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting lock, the same offset and length that were provided
   in the arguments should be returned in the denied results.  The File
   Locking section contains further discussion of the file locking
   mechanisms.

   LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
   identify the owner.  This is because the client does not have to open
   the file to test for the existence of a lock, so a stateid may not be
   available.

   The test for conflicting locks should exclude locks for the current
   lockowner.  Note that since such locks are not examined the possible
   existence of overlapping ranges may not affect the results of LOCKT.
   If the server does examine locks that match the lockowner for the
   purpose of range checking, NFS4ERR_LOCK_RANGE may be returned..  In
   the event that it returns NFS4_OK, clients may do a LOCK and receive
   NFS4ERR_LOCK_RANGE on the LOCK request because of the flexibility
   provided to the server.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_RANGE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DENIED
      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCK_RANGE
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_CLIENTID







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14.2.12.  Operation 14: LOCKU - Unlock File

   SYNOPSIS

     (cfh) type, seqid, stateid, offset, length -> stateid

   ARGUMENT

     struct LOCKU4args {
             /* CURRENT_FH: file */
             nfs_lock_type4  locktype;
             seqid4          seqid;
             stateid4        stateid;
             offset4         offset;
             length4         length;
     };

   RESULT

     union LOCKU4res switch (nfsstat4 status) {
      case   NFS4_OK:
              stateid4       stateid;
      default:
              void;
     };

   DESCRIPTION

   The LOCKU operation unlocks the record lock specified by the
   parameters. The client may set the locktype field to any value that
   is legal for the nfs_lock_type4 enumerated type, and the server MUST
   accept any legal value for locktype. Any legal value for locktype has
   no effect on the success or failure of the LOCKU operation.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   If the area to be unlocked does not correspond exactly to a lock
   actually held by the lockowner the server may return the error
   NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
   locked, where the area is a sub-range of the area locked, where it
   overlaps the area locked without matching exactly or the area
   specified includes multiple locks held by the lockowner.  In all of



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   these cases, allowed by POSIX locking semantics, a client receiving
   this error, should if it desires support for such operations,
   simulate the operation using LOCKU on ranges corresponding to locks
   it actually holds, possibly followed by LOCK requests for the sub-
   ranges not being unlocked.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_RANGE
      NFS4ERR_BAD_SEQID
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_EXPIRED
      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCK_RANGE
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_OLD_STATEID
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID

14.2.13.  Operation 15: LOOKUP - Lookup Filename

   SYNOPSIS

     (cfh), component -> (cfh)

   ARGUMENT

     struct LOOKUP4args {
             /* CURRENT_FH: directory */
             component4      objname;
     };









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   RESULT

     struct LOOKUP4res {
             /* CURRENT_FH: object */
             nfsstat4        status;
     };

   DESCRIPTION

   This operation LOOKUPs or finds a filesystem object using the
   directory specified by the current filehandle.  LOOKUP evaluates the
   component and if the object exists the current filehandle is replaced
   with the component's filehandle.

   If the component cannot be evaluated either because it does not exist
   or because the client does not have permission to evaluate the
   component, then an error will be returned and the current filehandle
   will be unchanged.

   If the component is a zero length string or if any component does not
   obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   IMPLEMENTATION

   If the client wants to achieve the effect of a multi-component
   lookup, it may construct a COMPOUND request such as (and obtain each
   filehandle):

      PUTFH  (directory filehandle)
      LOOKUP "pub"
      GETFH
      LOOKUP "foo"
      GETFH
      LOOKUP "bar"
      GETFH

   NFS version 4 servers depart from the semantics of previous NFS
   versions in allowing LOOKUP requests to cross mountpoints on the
   server.  The client can detect a mountpoint crossing by comparing the
   fsid attribute of the directory with the fsid attribute of the
   directory looked up.  If the fsids are different then the new
   directory is a server mountpoint.  UNIX clients that detect a
   mountpoint crossing will need to mount the server's filesystem.  This
   needs to be done to maintain the file object identity checking
   mechanisms common to UNIX clients.






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   Servers that limit NFS access to "shares" or "exported" filesystems
   should provide a pseudo-filesystem into which the exported
   filesystems can be integrated, so that clients can browse the
   server's name space.  The clients' view of a pseudo filesystem will
   be limited to paths that lead to exported filesystems.

   Note: previous versions of the protocol assigned special semantics to
   the names "." and "..".  NFS version 4 assigns no special semantics
   to these names.  The LOOKUPP operator must be used to lookup a parent
   directory.

   Note that this operation does not follow symbolic links.  The client
   is responsible for all parsing of filenames including filenames that
   are modified by symbolic links encountered during the lookup process.

   If the current filehandle supplied is not a directory but a symbolic
   link, the error NFS4ERR_SYMLINK is returned as the error.  For all
   other non-directory file types, the error NFS4ERR_NOTDIR is returned.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADXDR
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTDIR
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_SYMLINK
      NFS4ERR_WRONGSEC

14.2.14.  Operation 16: LOOKUPP - Lookup Parent Directory

   SYNOPSIS

     (cfh) -> (cfh)






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   ARGUMENT

     /* CURRENT_FH: object */
     void;

   RESULT

     struct LOOKUPP4res {
             /* CURRENT_FH: directory */
             nfsstat4        status;
     };

   DESCRIPTION

   The current filehandle is assumed to refer to a regular directory
   or a named attribute directory.  LOOKUPP assigns the filehandle for
   its parent directory to be the current filehandle.  If there is no
   parent directory an NFS4ERR_NOENT error must be returned.
   Therefore, NFS4ERR_NOENT will be returned by the server when the
   current filehandle is at the root or top of the server's file tree.

   IMPLEMENTATION

   As for LOOKUP, LOOKUPP will also cross mountpoints.

   If the current filehandle is not a directory or named attribute
   directory, the error NFS4ERR_NOTDIR is returned.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_FHEXPIRED
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTDIR
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.15.  Operation 17: NVERIFY - Verify Difference in Attributes

   SYNOPSIS

     (cfh), fattr -> -




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   ARGUMENT

     struct NVERIFY4args {
             /* CURRENT_FH: object */
             fattr4          obj_attributes;
     };

   RESULT

     struct NVERIFY4res {
             nfsstat4        status;
     };

   DESCRIPTION

   This operation is used to prefix a sequence of operations to be
   performed if one or more attributes have changed on some filesystem
   object.  If all the attributes match then the error NFS4ERR_SAME must
   be returned.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   This operation is useful as a cache validation operator.  If the
   object to which the attributes belong has changed then the following
   operations may obtain new data associated with that object.  For
   instance, to check if a file has been changed and obtain new data if
   it has:

      PUTFH  (public)
      LOOKUP "foobar"
      NVERIFY attrbits attrs
      READ 0 32767

   In the case that a recommended attribute is specified in the NVERIFY
   operation and the server does not support that attribute for the
   filesystem object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.

   When the attribute rdattr_error or any write-only attribute (e.g.,
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.








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   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ATTRNOTSUPP
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_SAME
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.16.  Operation 18: OPEN - Open a Regular File

   SYNOPSIS

     (cfh), seqid, share_access, share_deny, owner, openhow, claim ->
     (cfh), stateid, cinfo, rflags, open_confirm, attrset delegation

   ARGUMENT

     struct OPEN4args {
             seqid4          seqid;
             uint32_t        share_access;
             uint32_t        share_deny;
             open_owner4     owner;
             openflag4       openhow;
             open_claim4     claim;
     };

     enum createmode4 {
             UNCHECKED4      = 0,
             GUARDED4        = 1,
             EXCLUSIVE4      = 2
     };

     union createhow4 switch (createmode4 mode) {
      case UNCHECKED4:
      case GUARDED4:
              fattr4         createattrs;
      case EXCLUSIVE4:
              verifier4      createverf;



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     };

     enum opentype4 {
             OPEN4_NOCREATE  = 0,
             OPEN4_CREATE    = 1
     };

     union openflag4 switch (opentype4 opentype) {
      case OPEN4_CREATE:
              createhow4     how;
      default:
              void;
     };

     /* Next definitions used for OPEN delegation */
     enum limit_by4 {
             NFS_LIMIT_SIZE          = 1,
             NFS_LIMIT_BLOCKS        = 2
             /* others as needed */
     };

     struct nfs_modified_limit4 {
             uint32_t        num_blocks;
             uint32_t        bytes_per_block;
     };

     union nfs_space_limit4 switch (limit_by4 limitby) {
      /* limit specified as file size */
      case NFS_LIMIT_SIZE:
              uint64_t               filesize;
      /* limit specified by number of blocks */
      case NFS_LIMIT_BLOCKS:
              nfs_modified_limit4    mod_blocks;
     } ;

     enum open_delegation_type4 {
             OPEN_DELEGATE_NONE      = 0,
             OPEN_DELEGATE_READ      = 1,
             OPEN_DELEGATE_WRITE     = 2
     };

     enum open_claim_type4 {
             CLAIM_NULL              = 0,
             CLAIM_PREVIOUS          = 1,
             CLAIM_DELEGATE_CUR      = 2,
             CLAIM_DELEGATE_PREV     = 3
     };




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     struct open_claim_delegate_cur4 {
             stateid4        delegate_stateid;
             component4      file;
     };

     union open_claim4 switch (open_claim_type4 claim) {
      /*
       * No special rights to file. Ordinary OPEN of the specified file.
       */
      case CLAIM_NULL:
              /* CURRENT_FH: directory */
              component4     file;

      /*
       * Right to the file established by an open previous to server
       * reboot.  File identified by filehandle obtained at that time
       * rather than by name.
       */
      case CLAIM_PREVIOUS:
              /* CURRENT_FH: file being reclaimed */
              open_delegation_type4   delegate_type;

      /*
       * Right to file based on a delegation granted by the server.
       * File is specified by name.
       */
      case CLAIM_DELEGATE_CUR:
              /* CURRENT_FH: directory */
              open_claim_delegate_cur4       delegate_cur_info;

      /* Right to file based on a delegation granted to a previous boot
       * instance of the client.  File is specified by name.
       */
      case CLAIM_DELEGATE_PREV:
              /* CURRENT_FH: directory */
              component4     file_delegate_prev;
     };

   RESULT

   struct open_read_delegation4 {
           stateid4        stateid;        /* Stateid for delegation*/
           bool            recall;         /* Pre-recalled flag for
                                              delegations obtained
                                              by reclaim
                                              (CLAIM_PREVIOUS) */
           nfsace4         permissions;    /* Defines users who don't
                                              need an ACCESS call to



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                                              open for read */
   };

   struct open_write_delegation4 {
           stateid4        stateid;        /* Stateid for delegation*/
           bool            recall;         /* Pre-recalled flag for
                                              delegations obtained
                                              by reclaim
                                              (CLAIM_PREVIOUS) */
           nfs_space_limit4 space_limit;   /* Defines condition that
                                              the client must check to
                                              determine whether the
                                              file needs to be flushed
                                              to the server on close.
                                              */
           nfsace4         permissions;    /* Defines users who don't
                                              need an ACCESS call as
                                              part of a delegated
                                              open. */
   };

   union open_delegation4
   switch (open_delegation_type4 delegation_type) {
           case OPEN_DELEGATE_NONE:
                   void;
           case OPEN_DELEGATE_READ:
                   open_read_delegation4 read;
           case OPEN_DELEGATE_WRITE:
                   open_write_delegation4 write;
   };

   const OPEN4_RESULT_CONFIRM      = 0x00000002;
   const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;

   struct OPEN4resok {
           stateid4        stateid;        /* Stateid for open */
           change_info4    cinfo;          /* Directory Change Info */
           uint32_t        rflags;         /* Result flags */
           bitmap4         attrset;        /* attributes on create */
           open_delegation4 delegation;    /* Info on any open
                                              delegation */
   };

   union OPEN4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* CURRENT_FH: opened file */
           OPEN4resok      resok4;
    default:



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           void;
   };

   WARNING TO CLIENT IMPLEMENTORS

   OPEN resembles LOOKUP in that it generates a filehandle for the
   client to use.  Unlike LOOKUP though, OPEN creates server state on
   the filehandle.  In normal circumstances, the client can only release
   this state with a CLOSE operation.  CLOSE uses the current filehandle
   to determine which file to close.  Therefore the client MUST follow
   every OPEN operation with a GETFH operation in the same COMPOUND
   procedure.  This will supply the client with the filehandle such that
   CLOSE can be used appropriately.

   Simply waiting for the lease on the file to expire is insufficient
   because the server may maintain the state indefinitely as long as
   another client does not attempt to make a conflicting access to the
   same file.

   DESCRIPTION

   The OPEN operation creates and/or opens a regular file in a directory
   with the provided name.  If the file does not exist at the server and
   creation is desired, specification of the method of creation is
   provided by the openhow parameter.  The client has the choice of
   three creation methods: UNCHECKED, GUARDED, or EXCLUSIVE.

   If the current filehandle is a named attribute directory, OPEN will
   then create or open a named attribute file.  Note that exclusive
   create of a named attribute is not supported.  If the createmode is
   EXCLUSIVE4 and the current filehandle is a named attribute directory,
   the server will return EINVAL.

   UNCHECKED means that the file should be created if a file of that
   name does not exist and encountering an existing regular file of that
   name is not an error.  For this type of create, createattrs specifies
   the initial set of attributes for the file.  The set of attributes
   may include any writable attribute valid for regular files.  When an
   UNCHECKED create encounters an existing file, the attributes
   specified by createattrs are not used, except that when an size of
   zero is specified, the existing file is truncated.  If GUARDED is
   specified, the server checks for the presence of a duplicate object
   by name before performing the create.  If a duplicate exists, an
   error of NFS4ERR_EXIST is returned as the status.  If the object does
   not exist, the request is performed as described for UNCHECKED.  For






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   each of these cases (UNCHECKED and GUARDED) where the operation is
   successful, the server will return to the client an attribute mask
   signifying which attributes were successfully set for the object.

   EXCLUSIVE specifies that the server is to follow exclusive creation
   semantics, using the verifier to ensure exclusive creation of the
   target.  The server should check for the presence of a duplicate
   object by name.  If the object does not exist, the server creates the
   object and stores the verifier with the object.  If the object does
   exist and the stored verifier matches the client provided verifier,
   the server uses the existing object as the newly created object.  If
   the stored verifier does not match, then an error of NFS4ERR_EXIST is
   returned.  No attributes may be provided in this case, since the
   server may use an attribute of the target object to store the
   verifier.  If the server uses an attribute to store the exclusive
   create verifier, it will signify which attribute by setting the
   appropriate bit in the attribute mask that is returned in the
   results.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 struct, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   Upon successful creation, the current filehandle is replaced by that
   of the new object.

   The OPEN operation provides for Windows share reservation capability
   with the use of the share_access and share_deny fields of the OPEN
   arguments.  The client specifies at OPEN the required share_access
   and share_deny modes.  For clients that do not directly support
   SHAREs (i.e., UNIX), the expected deny value is DENY_NONE.  In the
   case that there is a existing SHARE reservation that conflicts with
   the OPEN request, the server returns the error NFS4ERR_SHARE_DENIED.
   For a complete SHARE request, the client must provide values for the
   owner and seqid fields for the OPEN argument.  For additional
   discussion of SHARE semantics see the section on 'Share
   Reservations'.

   In the case that the client is recovering state from a server
   failure, the claim field of the OPEN argument is used to signify that
   the request is meant to reclaim state previously held.

   The "claim" field of the OPEN argument is used to specify the file to
   be opened and the state information which the client claims to
   possess.  There are four basic claim types which cover the various
   situations for an OPEN.  They are as follows:




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   CLAIM_NULL
                         For the client, this is a new OPEN
                         request and there is no previous state
                         associate with the file for the client.

   CLAIM_PREVIOUS
                         The client is claiming basic OPEN state
                         for a file that was held previous to a
                         server reboot.  Generally used when a
                         server is returning persistent
                         filehandles; the client may not have the
                         file name to reclaim the OPEN.

   CLAIM_DELEGATE_CUR
                         The client is claiming a delegation for
                         OPEN as granted by the server.
                         Generally this is done as part of
                         recalling a delegation.

   CLAIM_DELEGATE_PREV
                         The client is claiming a delegation
                         granted to a previous client instance;
                         used after the client reboots. The
                         server MAY support CLAIM_DELEGATE_PREV.
                         If it does support CLAIM_DELEGATE_PREV,
                         SETCLIENTID_CONFIRM MUST NOT remove the
                         client's delegation state, and the
                         server MUST support the DELEGPURGE
                         operation.

   For OPEN requests whose claim type is other than CLAIM_PREVIOUS
   (i.e., requests other than those devoted to reclaiming opens after a
   server reboot) that reach the server during its grace or lease
   expiration period, the server returns an error of NFS4ERR_GRACE.

   For any OPEN request, the server may return an open delegation, which
   allows further opens and closes to be handled locally on the client
   as described in the section Open Delegation.  Note that delegation is
   up to the server to decide.  The client should never assume that
   delegation will or will not be granted in a particular instance.  It
   should always be prepared for either case.  A partial exception is
   the reclaim (CLAIM_PREVIOUS) case, in which a delegation type is
   claimed.  In this case, delegation will always be granted, although
   the server may specify an immediate recall in the delegation
   structure.

   The rflags returned by a successful OPEN allow the server to return
   information governing how the open file is to be handled.



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   OPEN4_RESULT_CONFIRM indicates that the client MUST execute an
   OPEN_CONFIRM operation before using the open file.
   OPEN4_RESULT_LOCKTYPE_POSIX indicates the server's file locking
   behavior supports the complete set of Posix locking techniques.  From
   this the client can choose to manage file locking state in a way to
   handle a mis-match of file locking management.

   If the component is of zero length, NFS4ERR_INVAL will be returned.
   The component is also subject to the normal UTF-8, character support,
   and name checks.  See the section "UTF-8 Related Errors" for further
   discussion.

   When an OPEN is done and the specified lockowner already has the
   resulting filehandle open, the result is to "OR" together the new
   share and deny status together with the existing status.  In this
   case, only a single CLOSE need be done, even though multiple OPENs
   were completed.  When such an OPEN is done, checking of share
   reservations for the new OPEN proceeds normally, with no exception
   for the existing OPEN held by the same lockowner.

   If the underlying filesystem at the server is only accessible in a
   read-only mode and the OPEN request has specified ACCESS_WRITE or
   ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
   only filesystem.

   As with the CREATE operation, the server MUST derive the owner, owner
   ACE, group, or group ACE if any of the four attributes are required
   and supported by the server's filesystem.  For an OPEN with the
   EXCLUSIVE4 createmode, the server has no choice, since such OPEN
   calls do not include the createattrs field.  Conversely, if
   createattrs is specified, and includes owner or group (or
   corresponding ACEs) that the principal in the RPC call's credentials
   does not have authorization to create files for, then the server may
   return NFS4ERR_PERM.

   In the case of a OPEN which specifies a size of zero (e.g.,
   truncation) and the file has named attributes, the named attributes
   are left as is.  They are not removed.

   IMPLEMENTATION

   The OPEN operation contains support for EXCLUSIVE create.  The
   mechanism is similar to the support in NFS version 3 [RFC1813].  As
   in NFS version 3, this mechanism provides reliable exclusive
   creation.  Exclusive create is invoked when the how parameter is
   EXCLUSIVE.  In this case, the client provides a verifier that can
   reasonably be expected to be unique.  A combination of a client




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   identifier, perhaps the client network address, and a unique number
   generated by the client, perhaps the RPC transaction identifier, may
   be appropriate.

   If the object does not exist, the server creates the object and
   stores the verifier in stable storage. For filesystems that do not
   provide a mechanism for the storage of arbitrary file attributes, the
   server may use one or more elements of the object meta-data to store
   the verifier. The verifier must be stored in stable storage to
   prevent erroneous failure on retransmission of the request. It is
   assumed that an exclusive create is being performed because exclusive
   semantics are critical to the application. Because of the expected
   usage, exclusive CREATE does not rely solely on the normally volatile
   duplicate request cache for storage of the verifier. The duplicate
   request cache in volatile storage does not survive a crash and may
   actually flush on a long network partition, opening failure windows.
   In the UNIX local filesystem environment, the expected storage
   location for the verifier on creation is the meta-data (time stamps)
   of the object. For this reason, an exclusive object create may not
   include initial attributes because the server would have nowhere to
   store the verifier.

   If the server can not support these exclusive create semantics,
   possibly because of the requirement to commit the verifier to stable
   storage, it should fail the OPEN request with the error,
   NFS4ERR_NOTSUPP.

   During an exclusive CREATE request, if the object already exists, the
   server reconstructs the object's verifier and compares it with the
   verifier in the request. If they match, the server treats the request
   as a success. The request is presumed to be a duplicate of an
   earlier, successful request for which the reply was lost and that the
   server duplicate request cache mechanism did not detect.  If the
   verifiers do not match, the request is rejected with the status,
   NFS4ERR_EXIST.

   Once the client has performed a successful exclusive create, it must
   issue a SETATTR to set the correct object attributes.  Until it does
   so, it should not rely upon any of the object attributes, since the
   server implementation may need to overload object meta-data to store
   the verifier.  The subsequent SETATTR must not occur in the same
   COMPOUND request as the OPEN.  This separation will guarantee that
   the exclusive create mechanism will continue to function properly in
   the face of retransmission of the request.

   Use of the GUARDED attribute does not provide exactly-once semantics.
   In particular, if a reply is lost and the server does not detect the
   retransmission of the request, the operation can fail with



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   NFS4ERR_EXIST, even though the create was performed successfully.
   The client would use this behavior in the case that the application
   has not requested an exclusive create but has asked to have the file
   truncated when the file is opened.  In the case of the client timing
   out and retransmitting the create request, the client can use GUARDED
   to prevent against a sequence like: create, write, create
   (retransmitted) from occurring.

   For SHARE reservations, the client must specify a value for
   share_access that is one of READ, WRITE, or BOTH.  For share_deny,
   the client must specify one of NONE, READ, WRITE, or BOTH.  If the
   client fails to do this, the server must return NFS4ERR_INVAL.

   Based on the share_access value (READ, WRITE, or BOTH) the client
   should check that the requester has the proper access rights to
   perform the specified operation.  This would generally be the results
   of applying the ACL access rules to the file for the current
   requester.  However, just as with the ACCESS operation, the client
   should not attempt to second-guess the server's decisions, as access
   rights may change and may be subject to server administrative
   controls outside the ACL framework.  If the requester is not
   authorized to READ or WRITE (depending on the share_access value),
   the server must return NFS4ERR_ACCESS.  Note that since the NFS
   version 4 protocol does not impose any requirement that READs and
   WRITEs issued for an open file have the same credentials as the OPEN
   itself, the server still must do appropriate access checking on the
   READs and WRITEs themselves.

   If the component provided to OPEN is a symbolic link, the error
   NFS4ERR_SYMLINK will be returned to the client.  If the current
   filehandle is not a directory, the error NFS4ERR_NOTDIR will be
   returned.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_ATTRNOTSUPP
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADOWNER
      NFS4ERR_BAD_SEQID
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_EXIST
      NFS4ERR_EXPIRED



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      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_IO
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_NOTDIR
      NFS4ERR_NOTSUPP
      NFS4ERR_NO_GRACE
      NFS4ERR_PERM
      NFS4ERR_RECLAIM_BAD
      NFS4ERR_RECLAIM_CONFLICT
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_SHARE_DENIED
      NFS4ERR_STALE
      NFS4ERR_STALE_CLIENTID
      NFS4ERR_SYMLINK
      NFS4ERR_WRONGSEC

14.2.17.  Operation 19: OPENATTR - Open Named Attribute Directory

   SYNOPSIS

     (cfh) createdir -> (cfh)

   ARGUMENT

     struct OPENATTR4args {
             /* CURRENT_FH: object */
             bool    createdir;
     };

   RESULT

     struct OPENATTR4res {
             /* CURRENT_FH: named attr directory*/
             nfsstat4        status;
     };






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   DESCRIPTION

   The OPENATTR operation is used to obtain the filehandle of the named
   attribute directory associated with the current filehandle.  The
   result of the OPENATTR will be a filehandle to an object of type
   NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
   be used to obtain filehandles for the various named attributes
   associated with the original filesystem object.  Filehandles returned
   within the named attribute directory will have a type of
   NF4NAMEDATTR.

   The createdir argument allows the client to signify if a named
   attribute directory should be created as a result of the OPENATTR
   operation.  Some clients may use the OPENATTR operation with a value
   of FALSE for createdir to determine if any named attributes exist for
   the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
   createdir has a value of TRUE and no named attribute directory
   exists, one is created.  The creation of a named attribute directory
   assumes that the server has implemented named attribute support in
   this fashion and is not required to do so by this definition.

   IMPLEMENTATION

   If the server does not support named attributes for the current
   filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
   client.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_FHEXPIRED
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_NOTSUPP
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE






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14.2.18.  Operation 20: OPEN_CONFIRM - Confirm Open

   SYNOPSIS

     (cfh), seqid, stateid-> stateid

   ARGUMENT

     struct OPEN_CONFIRM4args {
             /* CURRENT_FH: opened file */
             stateid4        open_stateid;
             seqid4          seqid;
     };

   RESULT

     struct OPEN_CONFIRM4resok {
             stateid4        open_stateid;
     };

     union OPEN_CONFIRM4res switch (nfsstat4 status) {
      case NFS4_OK:
              OPEN_CONFIRM4resok     resok4;
      default:
              void;
     };

   DESCRIPTION

   This operation is used to confirm the sequence id usage for the first
   time that a open_owner is used by a client.  The stateid returned
   from the OPEN operation is used as the argument for this operation
   along with the next sequence id for the open_owner.  The sequence id
   passed to the OPEN_CONFIRM must be 1 (one) greater than the seqid
   passed to the OPEN operation from which the open_confirm value was
   obtained.  If the server receives an unexpected sequence id with
   respect to the original open, then the server assumes that the client
   will not confirm the original OPEN and all state associated with the
   original OPEN is released by the server.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   A given client might generate many open_owner4 data structures for a
   given clientid.  The client will periodically either dispose of its
   open_owner4s or stop using them for indefinite periods of time.  The
   latter situation is why the NFS version 4 protocol does not have an



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   explicit operation to exit an open_owner4: such an operation is of no
   use in that situation.  Instead, to avoid unbounded memory use, the
   server needs to implement a strategy for disposing of open_owner4s
   that have no current lock, open, or delegation state for any files
   and have not been used recently.  The time period used to determine
   when to dispose of open_owner4s is an implementation choice.  The
   time period should certainly be no less than the lease time plus any
   grace period the server wishes to implement beyond a lease time.  The
   OPEN_CONFIRM operation allows the server to safely dispose of unused
   open_owner4 data structures.

   In the case that a client issues an OPEN operation and the server no
   longer has a record of the open_owner4, the server needs to ensure
   that this is a new OPEN and not a replay or retransmission.

   Servers must not require confirmation on OPENs that grant delegations
   or are doing reclaim operations.  See section "Use of Open
   Confirmation" for details.  The server can easily avoid this by
   noting whether it has disposed of one open_owner4 for the given
   clientid.  If the server does not support delegation, it might simply
   maintain a single bit that notes whether any open_owner4 (for any
   client) has been disposed of.

   The server must hold unconfirmed OPEN state until one of three events
   occur.  First, the client sends an OPEN_CONFIRM request with the
   appropriate sequence id and stateid within the lease period.  In this
   case, the OPEN state on the server goes to confirmed, and the
   open_owner4 on the server is fully established.

   Second, the client sends another OPEN request with a sequence id that
   is incorrect for the open_owner4 (out of sequence).  In this case,
   the server assumes the second OPEN request is valid and the first one
   is a replay.  The server cancels the OPEN state of the first OPEN
   request, establishes an unconfirmed OPEN state for the second OPEN
   request, and responds to the second OPEN request with an indication
   that an OPEN_CONFIRM is needed.  The process then repeats itself.
   While there is a potential for a denial of service attack on the
   client, it is mitigated if the client and server require the use of a
   security flavor based on Kerberos V5, LIPKEY, or some other flavor
   that uses cryptography.

   What if the server is in the unconfirmed OPEN state for a given
   open_owner4, and it receives an operation on the open_owner4 that has
   a stateid but the operation is not OPEN, or it is OPEN_CONFIRM but
   with the wrong stateid?  Then, even if the seqid is correct, the






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   server returns NFS4ERR_BAD_STATEID, because the server assumes the
   operation is a replay: if the server has no established OPEN state,
   then there is no way, for example, a LOCK operation could be valid.

   Third, neither of the two aforementioned events occur for the
   open_owner4 within the lease period.  In this case, the OPEN state is
   canceled and disposal of the open_owner4 can occur.

   ERRORS

      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_SEQID
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_EXPIRED
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_OLD_STATEID
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID

14.2.19.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access

   SYNOPSIS

     (cfh), stateid, seqid, access, deny -> stateid

   ARGUMENT

     struct OPEN_DOWNGRADE4args {
             /* CURRENT_FH: opened file */
             stateid4        open_stateid;
             seqid4          seqid;
             uint32_t        share_access;
             uint32_t        share_deny;
     };

   RESULT

     struct OPEN_DOWNGRADE4resok {
             stateid4        open_stateid;
     };



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     union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
      case NFS4_OK:
             OPEN_DOWNGRADE4resok    resok4;
      default:
             void;
     };

   DESCRIPTION

   This operation is used to adjust the share_access and share_deny bits
   for a given open.  This is necessary when a given openowner opens the
   same file multiple times with different share_access and share_deny
   flags.  In this situation, a close of one of the opens may change the
   appropriate share_access and share_deny flags to remove bits
   associated with opens no longer in effect.

   The share_access and share_deny bits specified in this operation
   replace the current ones for the specified open file.  The
   share_access and share_deny bits specified must be exactly equal to
   the union of the share_access and share_deny bits specified for some
   subset of the OPENs in effect for current openowner on the current
   file.  If that constraint is not respected, the error NFS4ERR_INVAL
   should be returned.  Since share_access and share_deny bits are
   subsets of those already granted, it is not possible for this request
   to be denied because of conflicting share reservations.

   On success, the current filehandle retains its value.

   ERRORS

      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_SEQID
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_EXPIRED
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_OLD_STATEID
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID






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14.2.20.  Operation 22: PUTFH - Set Current Filehandle

   SYNOPSIS

     filehandle -> (cfh)

   ARGUMENT

     struct PUTFH4args {
             nfs_fh4         object;
     };

   RESULT

     struct PUTFH4res {
             /* CURRENT_FH: */
             nfsstat4        status;
     };

   DESCRIPTION

   Replaces the current filehandle with the filehandle provided as an
   argument.

   If the security mechanism used by the requester does not meet the
   requirements of the filehandle provided to this operation, the server
   MUST return NFS4ERR_WRONGSEC.

   IMPLEMENTATION

   Commonly used as the first operator in an NFS request to set the
   context for following operations.

   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_FHEXPIRED
      NFS4ERR_MOVED
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_WRONGSEC








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14.2.21.  Operation 23: PUTPUBFH - Set Public Filehandle

   SYNOPSIS

     - -> (cfh)

   ARGUMENT

     void;

   RESULT

     struct PUTPUBFH4res {
             /* CURRENT_FH: public fh */
             nfsstat4        status;
     };

   DESCRIPTION

   Replaces the current filehandle with the filehandle that represents
   the public filehandle of the server's name space.  This filehandle
   may be different from the "root" filehandle which may be associated
   with some other directory on the server.

   The public filehandle represents the concepts embodied in [RFC2054],
   [RFC2055], [RFC2224].  The intent for NFS version 4 is that the
   public filehandle (represented by the PUTPUBFH operation) be used as
   a method of providing WebNFS server compatibility with NFS versions 2
   and 3.

   The public filehandle and the root filehandle (represented by the
   PUTROOTFH operation) should be equivalent.  If the public and root
   filehandles are not equivalent, then the public filehandle MUST be a
   descendant of the root filehandle.

   IMPLEMENTATION

   Used as the first operator in an NFS request to set the context for
   following operations.

   With the NFS version 2 and 3 public filehandle, the client is able to
   specify whether the path name provided in the LOOKUP should be
   evaluated as either an absolute path relative to the server's root or
   relative to the public filehandle.  [RFC2224] contains further
   discussion of the functionality.  With NFS version 4, that type of
   specification is not directly available in the LOOKUP operation.  The
   reason for this is because the component separators needed to specify
   absolute vs. relative are not allowed in NFS version 4.  Therefore,



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   the client is responsible for constructing its request such that the
   use of either PUTROOTFH or PUTPUBFH are used to signify absolute or
   relative evaluation of an NFS URL respectively.

   Note that there are warnings mentioned in [RFC2224] with respect to
   the use of absolute evaluation and the restrictions the server may
   place on that evaluation with respect to how much of its namespace
   has been made available.  These same warnings apply to NFS version 4.
   It is likely, therefore that because of server implementation
   details, an NFS version 3 absolute public filehandle lookup may
   behave differently than an NFS version 4 absolute resolution.

   There is a form of security negotiation as described in [RFC2755]
   that uses the public filehandle a method of employing SNEGO.  This
   method is not available with NFS version 4 as filehandles are not
   overloaded with special meaning and therefore do not provide the same
   framework as NFS versions 2 and 3.  Clients should therefore use the
   security negotiation mechanisms described in this RFC.

   ERRORS

      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_WRONGSEC

14.2.22.  Operation 24: PUTROOTFH - Set Root Filehandle

   SYNOPSIS

     - -> (cfh)

   ARGUMENT

     void;

   RESULT

     struct PUTROOTFH4res {
             /* CURRENT_FH: root fh */
             nfsstat4        status;
     };










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   DESCRIPTION

   Replaces the current filehandle with the filehandle that represents
   the root of the server's name space.  From this filehandle a LOOKUP
   operation can locate any other filehandle on the server. This
   filehandle may be different from the "public" filehandle which may be
   associated with some other directory on the server.

   IMPLEMENTATION

   Commonly used as the first operator in an NFS request to set the
   context for following operations.

   ERRORS

      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_WRONGSEC

14.2.23.  Operation 25: READ - Read from File

   SYNOPSIS

     (cfh), stateid, offset, count -> eof, data

   ARGUMENT

     struct READ4args {
             /* CURRENT_FH: file */
             stateid4        stateid;
             offset4         offset;
             count4          count;
     };

   RESULT

     struct READ4resok {
             bool            eof;
             opaque          data<>;
     };

     union READ4res switch (nfsstat4 status) {
      case NFS4_OK:
              READ4resok     resok4;
      default:
              void;
     };




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   DESCRIPTION

   The READ operation reads data from the regular file identified by the
   current filehandle.

   The client provides an offset of where the READ is to start and a
   count of how many bytes are to be read.  An offset of 0 (zero) means
   to read data starting at the beginning of the file.  If offset is
   greater than or equal to the size of the file, the status, NFS4_OK,
   is returned with a data length set to 0 (zero) and eof is set to
   TRUE.  The READ is subject to access permissions checking.

   If the client specifies a count value of 0 (zero), the READ succeeds
   and returns 0 (zero) bytes of data again subject to access
   permissions checking.  The server may choose to return fewer bytes
   than specified by the client.  The client needs to check for this
   condition and handle the condition appropriately.

   The stateid value for a READ request represents a value returned from
   a previous record lock or share reservation request.  The stateid is
   used by the server to verify that the associated share reservation
   and any record locks are still valid and to update lease timeouts for
   the client.

   If the read ended at the end-of-file (formally, in a correctly formed
   READ request, if offset + count is equal to the size of the file), or
   the read request extends beyond the size of the file (if offset +
   count is greater than the size of the file), eof is returned as TRUE;
   otherwise it is FALSE.  A successful READ of an empty file will
   always return eof as TRUE.

   If the current filehandle is not a regular file, an error will be
   returned to the client.  In the case the current filehandle
   represents a directory, NFS4ERR_ISDIR is return; otherwise,
   NFS4ERR_INVAL is returned.

   For a READ with a stateid value of all bits 0, the server MAY allow
   the READ to be serviced subject to mandatory file locks or the
   current share deny modes for the file.  For a READ with a stateid
   value of all bits 1, the server MAY allow READ operations to bypass
   locking checks at the server.

   On success, the current filehandle retains its value.








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   IMPLEMENTATION

   It is possible for the server to return fewer than count bytes of
   data.  If the server returns less than the count requested and eof is
   set to FALSE, the client should issue another READ to get the
   remaining data.  A server may return less data than requested under
   several circumstances.  The file may have been truncated by another
   client or perhaps on the server itself, changing the file size from
   what the requesting client believes to be the case.  This would
   reduce the actual amount of data available to the client.  It is
   possible that the server may back off the transfer size and reduce
   the read request return.  Server resource exhaustion may also occur
   necessitating a smaller read return.

   If mandatory file locking is on for the file, and if the region
   corresponding to the data to be read from file is write locked by an
   owner not associated the stateid, the server will return the
   NFS4ERR_LOCKED error.  The client should try to get the appropriate
   read record lock via the LOCK operation before re-attempting the
   READ.  When the READ completes, the client should release the record
   lock via LOCKU.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_EXPIRED
      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_IO
      NFS4ERR_INVAL
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCKED
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NXIO
      NFS4ERR_OLD_STATEID
      NFS4ERR_OPENMODE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID




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14.2.24.  Operation 26: READDIR - Read Directory

   SYNOPSIS
      (cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
      cookieverf { cookie, name, attrs }

   ARGUMENT

     struct READDIR4args {
             /* CURRENT_FH: directory */
             nfs_cookie4     cookie;
             verifier4       cookieverf;
             count4          dircount;
             count4          maxcount;
             bitmap4         attr_request;
     };

   RESULT

     struct entry4 {
             nfs_cookie4     cookie;
             component4      name;
             fattr4          attrs;
             entry4          *nextentry;
     };

     struct dirlist4 {
             entry4          *entries;
             bool            eof;
     };

     struct READDIR4resok {
             verifier4       cookieverf;
             dirlist4        reply;
     };


     union READDIR4res switch (nfsstat4 status) {
      case NFS4_OK:
              READDIR4resok  resok4;
      default:
              void;
     };








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   DESCRIPTION

   The READDIR operation retrieves a variable number of entries from a
   filesystem directory and returns client requested attributes for each
   entry along with information to allow the client to request
   additional directory entries in a subsequent READDIR.

   The arguments contain a cookie value that represents where the
   READDIR should start within the directory.  A value of 0 (zero) for
   the cookie is used to start reading at the beginning of the
   directory.  For subsequent READDIR requests, the client specifies a
   cookie value that is provided by the server on a previous READDIR
   request.

   The cookieverf value should be set to 0 (zero) when the cookie value
   is 0 (zero) (first directory read).  On subsequent requests, it
   should be a cookieverf as returned by the server.  The cookieverf
   must match that returned by the READDIR in which the cookie was
   acquired.  If the server determines that the cookieverf is no longer
   valid for the directory, the error NFS4ERR_NOT_SAME must be returned.

   The dircount portion of the argument is a hint of the maximum number
   of bytes of directory information that should be returned.  This
   value represents the length of the names of the directory entries and
   the cookie value for these entries.  This length represents the XDR
   encoding of the data (names and cookies) and not the length in the
   native format of the server.

   The maxcount value of the argument is the maximum number of bytes for
   the result.  This maximum size represents all of the data being
   returned within the READDIR4resok structure and includes the XDR
   overhead.  The server may return less data.  If the server is unable
   to return a single directory entry within the maxcount limit, the
   error NFS4ERR_TOOSMALL will be returned to the client.

   Finally, attr_request represents the list of attributes to be
   returned for each directory entry supplied by the server.

   On successful return, the server's response will provide a list of
   directory entries.  Each of these entries contains the name of the
   directory entry, a cookie value for that entry, and the associated
   attributes as requested.  The "eof" flag has a value of TRUE if there
   are no more entries in the directory.

   The cookie value is only meaningful to the server and is used as a
   "bookmark" for the directory entry.  As mentioned, this cookie is
   used by the client for subsequent READDIR operations so that it may
   continue reading a directory.  The cookie is similar in concept to a



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   READ offset but should not be interpreted as such by the client.
   Ideally, the cookie value should not change if the directory is
   modified since the client may be caching these values.

   In some cases, the server may encounter an error while obtaining the
   attributes for a directory entry.  Instead of returning an error for
   the entire READDIR operation, the server can instead return the
   attribute 'fattr4_rdattr_error'.  With this, the server is able to
   communicate the failure to the client and not fail the entire
   operation in the instance of what might be a transient failure.
   Obviously, the client must request the fattr4_rdattr_error attribute
   for this method to work properly.  If the client does not request the
   attribute, the server has no choice but to return failure for the
   entire READDIR operation.

   For some filesystem environments, the directory entries "." and ".."
   have special meaning and in other environments, they may not.  If the
   server supports these special entries within a directory, they should
   not be returned to the client as part of the READDIR response.  To
   enable some client environments, the cookie values of 0, 1, and 2 are
   to be considered reserved.  Note that the UNIX client will use these
   values when combining the server's response and local representations
   to enable a fully formed UNIX directory presentation to the
   application.

   For READDIR arguments, cookie values of 1 and 2 should not be used
   and for READDIR results cookie values of 0, 1, and 2 should not be
   returned.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   The server's filesystem directory representations can differ greatly.
   A client's programming interfaces may also be bound to the local
   operating environment in a way that does not translate well into the
   NFS protocol.  Therefore the use of the dircount and maxcount fields
   are provided to allow the client the ability to provide guidelines to
   the server.  If the client is aggressive about attribute collection
   during a READDIR, the server has an idea of how to limit the encoded
   response.  The dircount field provides a hint on the number of
   entries based solely on the names of the directory entries.  Since it
   is a hint, it may be possible that a dircount value is zero.  In this
   case, the server is free to ignore the dircount value and return
   directory information based on the specified maxcount value.






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   The cookieverf may be used by the server to help manage cookie values
   that may become stale.  It should be a rare occurrence that a server
   is unable to continue properly reading a directory with the provided
   cookie/cookieverf pair.  The server should make every effort to avoid
   this condition since the application at the client may not be able to
   properly handle this type of failure.

   The use of the cookieverf will also protect the client from using
   READDIR cookie values that may be stale.  For example, if the file
   system has been migrated, the server may or may not be able to use
   the same cookie values to service READDIR as the previous server
   used.  With the client providing the cookieverf, the server is able
   to provide the appropriate response to the client.  This prevents the
   case where the server may accept a cookie value but the underlying
   directory has changed and the response is invalid from the client's
   context of its previous READDIR.

   Since some servers will not be returning "." and ".." entries as has
   been done with previous versions of the NFS protocol, the client that
   requires these entries be present in READDIR responses must fabricate
   them.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_COOKIE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTDIR
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_TOOSMALL

14.2.25.  Operation 27: READLINK - Read Symbolic Link

   SYNOPSIS

     (cfh) -> linktext






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   ARGUMENT

     /* CURRENT_FH: symlink */
     void;

   RESULT

     struct READLINK4resok {
             linktext4       link;
     };

     union READLINK4res switch (nfsstat4 status) {
      case NFS4_OK:
              READLINK4resok resok4;
      default:
              void;
     };

   DESCRIPTION

   READLINK reads the data associated with a symbolic link.  The data is
   a UTF-8 string that is opaque to the server.  That is, whether
   created by an NFS client or created locally on the server, the data
   in a symbolic link is not interpreted when created, but is simply
   stored.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   A symbolic link is nominally a pointer to another file.  The data is
   not necessarily interpreted by the server, just stored in the file.
   It is possible for a client implementation to store a path name that
   is not meaningful to the server operating system in a symbolic link.
   A READLINK operation returns the data to the client for
   interpretation. If different implementations want to share access to
   symbolic links, then they must agree on the interpretation of the
   data in the symbolic link.

   The READLINK operation is only allowed on objects of type NF4LNK.
   The server should return the error, NFS4ERR_INVAL, if the object is
   not of type, NF4LNK.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADHANDLE
      NFS4ERR_DELAY



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      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_ISDIR
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTSUPP
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.26.  Operation 28: REMOVE - Remove Filesystem Object

   SYNOPSIS

     (cfh), filename -> change_info

   ARGUMENT

     struct REMOVE4args {
             /* CURRENT_FH: directory */
             component4       target;
     };

   RESULT

     struct REMOVE4resok {
             change_info4    cinfo;
     }

     union REMOVE4res switch (nfsstat4 status) {
      case NFS4_OK:
              REMOVE4resok   resok4;
      default:
              void;
     }

   DESCRIPTION

   The REMOVE operation removes (deletes) a directory entry named by
   filename from the directory corresponding to the current filehandle.
   If the entry in the directory was the last reference to the
   corresponding filesystem object, the object may be destroyed.








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   For the directory where the filename was removed, the server returns
   change_info4 information in cinfo.  With the atomic field of the
   change_info4 struct, the server will indicate if the before and after
   change attributes were obtained atomically with respect to the
   removal.

   If the target has a length of 0 (zero), or if target does not obey
   the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   NFS versions 2 and 3 required a different operator RMDIR for
   directory removal and REMOVE for non-directory removal. This allowed
   clients to skip checking the file type when being passed a non-
   directory delete system call (e.g., unlink() in POSIX) to remove a
   directory, as well as the converse (e.g., a rmdir() on a non-
   directory) because they knew the server would check the file type.
   NFS version 4 REMOVE can be used to delete any directory entry
   independent of its file type. The implementor of an NFS version 4
   client's entry points from the unlink() and rmdir() system calls
   should first check the file type against the types the system call is
   allowed to remove before issuing a REMOVE. Alternatively, the
   implementor can produce a COMPOUND call that includes a LOOKUP/VERIFY
   sequence to verify the file type before a REMOVE operation in the
   same COMPOUND call.

   The concept of last reference is server specific.  However, if the
   numlinks field in the previous attributes of the object had the value
   1, the client should not rely on referring to the object via a
   filehandle.  Likewise, the client should not rely on the resources
   (disk space, directory entry, and so on) formerly associated with the
   object becoming immediately available.  Thus, if a client needs to be
   able to continue to access a file after using REMOVE to remove it,
   the client should take steps to make sure that the file will still be
   accessible.  The usual mechanism used is to RENAME the file from its
   old name to a new hidden name.

   If the server finds that the file is still open when the REMOVE
   arrives:

   o  The server SHOULD NOT delete the file's directory entry if the
      file was opened with OPEN4_SHARE_DENY_WRITE or
      OPEN4_SHARE_DENY_BOTH.






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   o  If the file was not opened with OPEN4_SHARE_DENY_WRITE or
      OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
      directory entry.  However, until last CLOSE of the file, the
      server MAY continue to allow access to the file via its
      filehandle.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_FHEXPIRED
      NFS4ERR_FILE_OPEN
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTDIR
      NFS4ERR_NOTEMPTY
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.27.  Operation 29: RENAME - Rename Directory Entry

   SYNOPSIS

     (sfh), oldname, (cfh), newname -> source_change_info,
     target_change_info

   ARGUMENT

     struct RENAME4args {
             /* SAVED_FH: source directory */
             component4      oldname;
             /* CURRENT_FH: target directory */
             component4      newname;
     };







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   RESULT

     struct RENAME4resok {
             change_info4    source_cinfo;
             change_info4    target_cinfo;
     };

     union RENAME4res switch (nfsstat4 status) {
      case NFS4_OK:
              RENAME4resok   resok4;
      default:
              void;
     };

   DESCRIPTION

   The RENAME operation renames the object identified by oldname in the
   source directory corresponding to the saved filehandle, as set by the
   SAVEFH operation, to newname in the target directory corresponding to
   the current filehandle.  The operation is required to be atomic to
   the client.  Source and target directories must reside on the same
   filesystem on the server.  On success, the current filehandle will
   continue to be the target directory.

   If the target directory already contains an entry with the name,
   newname, the source object must be compatible with the target:
   either both are non-directories or both are directories and the
   target must be empty.  If compatible, the existing target is removed
   before the rename occurs (See the IMPLEMENTATION subsection of the
   section "Operation 28: REMOVE - Remove Filesystem Object" for client
   and server actions whenever a target is removed).  If they are not
   compatible or if the target is a directory but not empty, the server
   will return the error, NFS4ERR_EXIST.

   If oldname and newname both refer to the same file (they might be
   hard links of each other), then RENAME should perform no action and
   return success.

   For both directories involved in the RENAME, the server returns
   change_info4 information.  With the atomic field of the change_info4
   struct, the server will indicate if the before and after change
   attributes were obtained atomically with respect to the rename.

   If the oldname refers to a named attribute and the saved and current
   filehandles refer to different filesystem objects, the server will
   return NFS4ERR_XDEV just as if the saved and current filehandles
   represented directories on different filesystems.




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   If the oldname or newname has a length of 0 (zero), or if oldname or
   newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
   will be returned.

   IMPLEMENTATION

   The RENAME operation must be atomic to the client.  The statement
   "source and target directories must reside on the same filesystem on
   the server" means that the fsid fields in the attributes for the
   directories are the same. If they reside on different filesystems,
   the error, NFS4ERR_XDEV, is returned.

   Based on the value of the fh_expire_type attribute for the object,
   the filehandle may or may not expire on a RENAME.  However, server
   implementors are strongly encouraged to attempt to keep filehandles
   from expiring in this fashion.

   On some servers, the file names "." and ".." are illegal as either
   oldname or newname, and will result in the error NFS4ERR_BADNAME.  In
   addition, on many servers the case of oldname or newname being an
   alias for the source directory will be checked for.  Such servers
   will return the error NFS4ERR_INVAL in these cases.

   If either of the source or target filehandles are not directories,
   the server will return NFS4ERR_NOTDIR.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_EXIST
      NFS4ERR_FHEXPIRED
      NFS4ERR_FILE_OPEN
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_NOTDIR
      NFS4ERR_NOTEMPTY
      NFS4ERR_RESOURCE



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      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_WRONGSEC
      NFS4ERR_XDEV

14.2.28.  Operation 30: RENEW - Renew a Lease

   SYNOPSIS

     clientid -> ()

   ARGUMENT

     struct RENEW4args {
             clientid4       clientid;
     };

   RESULT

     struct RENEW4res {
             nfsstat4        status;
     };

   DESCRIPTION

   The RENEW operation is used by the client to renew leases which it
   currently holds at a server.  In processing the RENEW request, the
   server renews all leases associated with the client.  The associated
   leases are determined by the clientid provided via the SETCLIENTID
   operation.

   IMPLEMENTATION

   When the client holds delegations, it needs to use RENEW to detect
   when the server has determined that the callback path is down.  When
   the server has made such a determination, only the RENEW operation
   will renew the lease on delegations.  If the server determines the
   callback path is down, it returns NFS4ERR_CB_PATH_DOWN.  Even though
   it returns NFS4ERR_CB_PATH_DOWN, the server MUST renew the lease on
   the record locks and share reservations that the client has
   established on the server.  If for some reason the lock and share
   reservation lease cannot be renewed, then the server MUST return an
   error other than NFS4ERR_CB_PATH_DOWN, even if the callback path is
   also down.






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   The client that issues RENEW MUST choose the principal, RPC security
   flavor, and if applicable, GSS-API mechanism and service via one of
   the following algorithms:

   o  The client uses the same principal, RPC security flavor -- and if
      the flavor was RPCSEC_GSS -- the same mechanism and service that
      was used when the client id was established via
      SETCLIENTID_CONFIRM.

   o  The client uses any principal, RPC security flavor mechanism and
      service combination that currently has an OPEN file on the server.
      I.e.,  the same principal had a successful OPEN operation, the
      file is still open by that principal, and the flavor, mechanism,
      and service of RENEW match that of the previous OPEN.

   The server MUST reject a RENEW that does not use one the
   aforementioned algorithms, with the error NFS4ERR_ACCESS.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADXDR
      NFS4ERR_CB_PATH_DOWN
      NFS4ERR_EXPIRED
      NFS4ERR_LEASE_MOVED
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE_CLIENTID

14.2.29.  Operation 31: RESTOREFH - Restore Saved Filehandle

   SYNOPSIS

     (sfh) -> (cfh)

   ARGUMENT

     /* SAVED_FH: */
     void;

   RESULT

     struct RESTOREFH4res {
             /* CURRENT_FH: value of saved fh */
             nfsstat4        status;
     };




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   DESCRIPTION

   Set the current filehandle to the value in the saved filehandle.  If
   there is no saved filehandle then return the error NFS4ERR_RESTOREFH.

   IMPLEMENTATION

   Operations like OPEN and LOOKUP use the current filehandle to
   represent a directory and replace it with a new filehandle.  Assuming
   the previous filehandle was saved with a SAVEFH operator, the
   previous filehandle can be restored as the current filehandle.  This
   is commonly used to obtain post-operation attributes for the
   directory, e.g.,

         PUTFH (directory filehandle)
         SAVEFH
         GETATTR attrbits     (pre-op dir attrs)
         CREATE optbits "foo" attrs
         GETATTR attrbits     (file attributes)
         RESTOREFH
         GETATTR attrbits     (post-op dir attrs)

   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_FHEXPIRED
      NFS4ERR_MOVED
      NFS4ERR_RESOURCE
      NFS4ERR_RESTOREFH
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_WRONGSEC

14.2.30.  Operation 32: SAVEFH - Save Current Filehandle

   SYNOPSIS

     (cfh) -> (sfh)

   ARGUMENT

     /* CURRENT_FH: */
     void;








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   RESULT

     struct SAVEFH4res {
             /* SAVED_FH: value of current fh */
             nfsstat4        status;
     };

   DESCRIPTION

   Save the current filehandle.  If a previous filehandle was saved then
   it is no longer accessible.  The saved filehandle can be restored as
   the current filehandle with the RESTOREFH operator.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_FHEXPIRED
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.31.  Operation 33: SECINFO - Obtain Available Security

   SYNOPSIS

     (cfh), name -> { secinfo }

   ARGUMENT

     struct SECINFO4args {
             /* CURRENT_FH: directory */
             component4     name;
     };

   RESULT

     enum rpc_gss_svc_t {/* From RFC 2203 */
             RPC_GSS_SVC_NONE        = 1,
             RPC_GSS_SVC_INTEGRITY   = 2,
             RPC_GSS_SVC_PRIVACY     = 3
     };




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     struct rpcsec_gss_info {
             sec_oid4        oid;
             qop4            qop;
             rpc_gss_svc_t   service;
     };

     union secinfo4 switch (uint32_t flavor) {
      case RPCSEC_GSS:
              rpcsec_gss_info        flavor_info;
      default:
              void;
     };

     typedef secinfo4 SECINFO4resok<>;

     union SECINFO4res switch (nfsstat4 status) {
      case NFS4_OK:
              SECINFO4resok resok4;
      default:
              void;
     };

   DESCRIPTION

   The SECINFO operation is used by the client to obtain a list of valid
   RPC authentication flavors for a specific directory filehandle, file
   name pair.  SECINFO should apply the same access methodology used for
   LOOKUP when evaluating the name.  Therefore, if the requester does
   not have the appropriate access to LOOKUP the name then SECINFO must
   behave the same way and return NFS4ERR_ACCESS.

   The result will contain an array which represents the security
   mechanisms available, with an order corresponding to server's
   preferences, the most preferred being first in the array. The client
   is free to pick whatever security mechanism it both desires and
   supports, or to pick in the server's preference order the first one
   it supports.  The array entries are represented by the secinfo4
   structure.  The field 'flavor' will contain a value of AUTH_NONE,
   AUTH_SYS (as defined in [RFC1831]), or RPCSEC_GSS (as defined in
   [RFC2203]).

   For the flavors AUTH_NONE and AUTH_SYS, no additional security
   information is returned.  For a return value of RPCSEC_GSS, a
   security triple is returned that contains the mechanism object id (as
   defined in [RFC2743]), the quality of protection (as defined in
   [RFC2743]) and the service type (as defined in [RFC2203]).  It is
   possible for SECINFO to return multiple entries with flavor equal to
   RPCSEC_GSS with different security triple values.



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   On success, the current filehandle retains its value.

   If the name has a length of 0 (zero), or if name does not obey the
   UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   IMPLEMENTATION

   The SECINFO operation is expected to be used by the NFS client when
   the error value of NFS4ERR_WRONGSEC is returned from another NFS
   operation.  This signifies to the client that the server's security
   policy is different from what the client is currently using.  At this
   point, the client is expected to obtain a list of possible security
   flavors and choose what best suits its policies.

   As mentioned, the server's security policies will determine when a
   client request receives NFS4ERR_WRONGSEC.  The operations which may
   receive this error are: LINK, LOOKUP, OPEN, PUTFH, PUTPUBFH,
   PUTROOTFH, RESTOREFH, RENAME, and indirectly READDIR.  LINK and
   RENAME will only receive this error if the security used for the
   operation is inappropriate for saved filehandle.  With the exception
   of READDIR, these operations represent the point at which the client
   can instantiate a filehandle into the "current filehandle" at the
   server.  The filehandle is either provided by the client (PUTFH,
   PUTPUBFH, PUTROOTFH) or generated as a result of a name to filehandle
   translation (LOOKUP and OPEN).  RESTOREFH is different because the
   filehandle is a result of a previous SAVEFH.  Even though the
   filehandle, for RESTOREFH, might have previously passed the server's
   inspection for a security match, the server will check it again on
   RESTOREFH to ensure that the security policy has not changed.

   If the client wants to resolve an error return of NFS4ERR_WRONGSEC,
   the following will occur:

   o  For LOOKUP and OPEN, the client will use SECINFO with the same
      current filehandle and name as provided in the original LOOKUP or
      OPEN to enumerate the available security triples.

   o  For LINK, PUTFH, RENAME, and RESTOREFH, the client will use
      SECINFO and provide the parent directory filehandle and object
      name which corresponds to the filehandle originally provided by
      the PUTFH RESTOREFH, or for LINK and RENAME, the SAVEFH.

   o  For PUTROOTFH and PUTPUBFH, the client will be unable to use the
      SECINFO operation since SECINFO requires a current filehandle and
      none exist for these two operations.  Therefore, the client must
      iterate through the security triples available at the client and
      reattempt the PUTROOTFH or PUTPUBFH operation. In the unfortunate
      event none of the MANDATORY security triples are supported by the



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      client and server, the client SHOULD try using others that support
      integrity. Failing that, the client can try using AUTH_NONE, but
      because such forms lack integrity checks, this puts the client at
      risk.  Nonetheless, the server SHOULD allow the client to use
      whatever security form the client requests and the server
      supports, since the risks of doing so are on the client.

   The READDIR operation will not directly return the NFS4ERR_WRONGSEC
   error.  However, if the READDIR request included a request for
   attributes, it is possible that the READDIR request's security triple
   does not match that of a directory entry.  If this is the case and
   the client has requested the rdattr_error attribute, the server will
   return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.

   See the section "Security Considerations" for a discussion on the
   recommendations for security flavor used by SECINFO.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADNAME
      NFS4ERR_BADXDR
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_MOVED
      NFS4ERR_NAMETOOLONG
      NFS4ERR_NOENT
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOTDIR
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.32.  Operation 34: SETATTR - Set Attributes

   SYNOPSIS

     (cfh), stateid, attrmask, attr_vals -> attrsset

   ARGUMENT

     struct SETATTR4args {
             /* CURRENT_FH: target object */
             stateid4        stateid;
             fattr4          obj_attributes;
     };



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   RESULT

     struct SETATTR4res {
             nfsstat4        status;
             bitmap4         attrsset;
     };

   DESCRIPTION

   The SETATTR operation changes one or more of the attributes of a
   filesystem object.  The new attributes are specified with a bitmap
   and the attributes that follow the bitmap in bit order.

   The stateid argument for SETATTR is used to provide file locking
   context that is necessary for SETATTR requests that set the size
   attribute.  Since setting the size attribute modifies the file's
   data, it has the same locking requirements as a corresponding WRITE.
   Any SETATTR that sets the size attribute is incompatible with a share
   reservation that specifies DENY_WRITE.  The area between the old
   end-of-file and the new end-of-file is considered to be modified just
   as would have been the case had the area in question been specified
   as the target of WRITE, for the purpose of checking conflicts with
   record locks, for those cases in which a server is implementing
   mandatory record locking behavior.  A valid stateid should always be
   specified.  When the file size attribute is not set, the special
   stateid consisting of all bits zero should be passed.

   On either success or failure of the operation, the server will return
   the attrsset bitmask to represent what (if any) attributes were
   successfully set.  The attrsset in the response is a subset of the
   bitmap4 that is part of the obj_attributes in the argument.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   If the request specifies the owner attribute to be set, the server
   should allow the operation to succeed if the current owner of the
   object matches the value specified in the request.  Some servers may
   be implemented in a way as to prohibit the setting of the owner
   attribute unless the requester has privilege to do so.  If the server
   is lenient in this one case of matching owner values, the client
   implementation may be simplified in cases of creation of an object
   followed by a SETATTR.

   The file size attribute is used to request changes to the size of a
   file. A value of 0 (zero) causes the file to be truncated, a value
   less than the current size of the file causes data from new size to



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   the end of the file to be discarded, and a size greater than the
   current size of the file causes logically zeroed data bytes to be
   added to the end of the file.  Servers are free to implement this
   using holes or actual zero data bytes. Clients should not make any
   assumptions regarding a server's implementation of this feature,
   beyond that the bytes returned will be zeroed.  Servers must support
   extending the file size via SETATTR.

   SETATTR is not guaranteed atomic.  A failed SETATTR may partially
   change a file's attributes.

   Changing the size of a file with SETATTR indirectly changes the
   time_modify.  A client must account for this as size changes can
   result in data deletion.

   The attributes time_access_set and time_modify_set are write-only
   attributes constructed as a switched union so the client can direct
   the server in setting the time values.  If the switched union
   specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
   be used for the operation.  If the switch union does not specify
   SET_TO_CLIENT_TIME4, the server is to use its current time for the
   SETATTR operation.

   If server and client times differ, programs that compare client time
   to file times can break. A time maintenance protocol should be used
   to limit client/server time skew.

   Use of a COMPOUND containing a VERIFY operation specifying only the
   change attribute, immediately followed by a SETATTR, provides a means
   whereby a client may specify a request that emulates the
   functionality of the SETATTR guard mechanism of NFS version 3.  Since
   the function of the guard mechanism is to avoid changes to the file
   attributes based on stale information, delays between checking of the
   guard condition and the setting of the attributes have the potential
   to compromise this function, as would the corresponding delay in the
   NFS version 4 emulation.  Therefore, NFS version 4 servers should
   take care to avoid such delays, to the degree possible, when
   executing such a request.

   If the server does not support an attribute as requested by the
   client, the server should return NFS4ERR_ATTRNOTSUPP.

   A mask of the attributes actually set is returned by SETATTR in all
   cases.  That mask must not include attributes bits not requested to
   be set by the client, and must be equal to the mask of attributes
   requested to be set only if the SETATTR completes without error.





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   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_ATTRNOTSUPP
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADOWNER
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_EXPIRED
      NFS4ERR_FBIG
      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_ISDIR
      NFS4ERR_LOCKED
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_OLD_STATEID
      NFS4ERR_OPENMODE
      NFS4ERR_PERM
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID

14.2.33.  Operation 35: SETCLIENTID - Negotiate Clientid

   SYNOPSIS

     client, callback, callback_ident -> clientid, setclientid_confirm

   ARGUMENT

     struct SETCLIENTID4args {
             nfs_client_id4  client;
             cb_client4      callback;
             uint32_t        callback_ident;
     };






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   RESULT

     struct SETCLIENTID4resok {
             clientid4       clientid;
             verifier4       setclientid_confirm;
     };

     union SETCLIENTID4res switch (nfsstat4 status) {
      case NFS4_OK:
              SETCLIENTID4resok      resok4;
      case NFS4ERR_CLID_INUSE:
              clientaddr4    client_using;
      default:
              void;
     };

   DESCRIPTION

   The client uses the SETCLIENTID operation to notify the server of its
   intention to use a particular client identifier, callback, and
   callback_ident for subsequent requests that entail creating lock,
   share reservation, and delegation state on the server.  Upon
   successful completion the server will return a shorthand clientid
   which, if confirmed via a separate step, will be used in subsequent
   file locking and file open requests. Confirmation of the clientid
   must be done via the SETCLIENTID_CONFIRM operation to return the
   clientid and setclientid_confirm values, as verifiers, to the server.
   The reason why two verifiers are necessary is that it is possible to
   use SETCLIENTID and SETCLIENTID_CONFIRM to modify the callback and
   callback_ident information but not the shorthand clientid.  In that
   event, the setclientid_confirm value is effectively the only
   verifier.

   The callback information provided in this operation will be used if
   the client is provided an open delegation at a future point.
   Therefore, the client must correctly reflect the program and port
   numbers for the callback program at the time SETCLIENTID is used.

   The callback_ident value is used by the server on the callback.  The
   client can leverage the callback_ident to eliminate the need for more
   than one callback RPC program number, while still being able to
   determine which server is initiating the callback.









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   IMPLEMENTATION

   To understand how to implement SETCLIENTID, make the following
   notations. Let:

   x be the value of the client.id subfield of the SETCLIENTID4args
     structure.

   v be the value of the client.verifier subfield of the
     SETCLIENTID4args structure.

   c be the value of the clientid field returned in the
     SETCLIENTID4resok structure.

   k represent the value combination of the fields callback and
     callback_ident fields of the SETCLIENTID4args structure.

   s be the setclientid_confirm value returned in the
     SETCLIENTID4resok structure.

   { v, x, c, k, s }
     be a quintuple for a client record. A client record is
     confirmed if there has been a SETCLIENTID_CONFIRM operation to
     confirm it.  Otherwise it is unconfirmed. An unconfirmed
     record is established by a SETCLIENTID call.

   Since SETCLIENTID is a non-idempotent operation, let us assume that
   the server is implementing the duplicate request cache (DRC).

   When the server gets a SETCLIENTID { v, x, k } request, it processes
   it in the following manner.

   o  It first looks up the request in the DRC. If there is a hit, it
      returns the result cached in the DRC.  The server does NOT remove
      client state (locks, shares, delegations) nor does it modify any
      recorded callback and callback_ident information for client { x }.

      For any DRC miss, the server takes the client id string x, and
      searches for client records for x that the server may have
      recorded from previous SETCLIENTID calls. For any confirmed record
      with the same id string x, if the recorded principal does not
      match that of SETCLIENTID call, then the server returns a
      NFS4ERR_CLID_INUSE error.

      For brevity of discussion, the remaining description of the
      processing assumes that there was a DRC miss, and that where the
      server has previously recorded a confirmed record for client x,
      the aforementioned principal check has successfully passed.



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   o  The server checks if it has recorded a confirmed record for { v,
      x, c, l, s }, where l may or may not equal k. If so, and since the
      id verifier v of the request matches that which is confirmed and
      recorded, the server treats this as a probable callback
      information update and records an unconfirmed { v, x, c, k, t }
      and leaves the confirmed { v, x, c, l, s } in place, such that t
      != s. It does not matter if k equals l or not.  Any pre-existing
      unconfirmed { v, x, c, *, * } is removed.

      The server returns { c, t }. It is indeed returning the old
      clientid4 value c, because the client apparently only wants to
      update callback value k to value l.  It's possible this request is
      one from the Byzantine router that has stale callback information,
      but this is not a problem.  The callback information update is
      only confirmed if followed up by a SETCLIENTID_CONFIRM { c, t }.

      The server awaits confirmation of k via
      SETCLIENTID_CONFIRM { c, t }.

      The server does NOT remove client (lock/share/delegation) state
      for x.

   o  The server has previously recorded a confirmed { u, x, c, l, s }
      record such that v != u, l may or may not equal k, and has not
      recorded any unconfirmed { *, x, *, *, * } record for x.  The
      server records an unconfirmed { v, x, d, k, t } (d != c, t != s).

      The server returns { d, t }.

      The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
      { d, t }.

      The server does NOT remove client (lock/share/delegation) state
      for x.

   o  The server has previously recorded a confirmed { u, x, c, l, s }
      record such that v != u, l may or may not equal k, and recorded an
      unconfirmed { w, x, d, m, t } record such that c != d, t != s, m
      may or may not equal k, m may or may not equal l, and k may or may
      not equal l. Whether w == v or w != v makes no difference.  The
      server simply removes the unconfirmed { w, x, d, m, t } record and
      replaces it with an unconfirmed { v, x, e, k, r } record, such
      that e != d, e != c, r != t, r != s.

      The server returns { e, r }.

      The server awaits confirmation of { e, k } via
      SETCLIENTID_CONFIRM { e, r }.



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      The server does NOT remove client (lock/share/delegation) state
      for x.

   o  The server has no confirmed { *, x, *, *, * } for x. It may or may
      not have recorded an unconfirmed { u, x, c, l, s }, where l may or
      may not equal k, and u may or may not equal v.  Any unconfirmed
      record { u, x, c, l, * }, regardless whether u == v or l == k, is
      replaced with an unconfirmed record { v, x, d, k, t } where d !=
      c, t != s.

      The server returns { d, t }.

      The server awaits confirmation of { d, k } via SETCLIENTID_CONFIRM
      { d, t }.  The server does NOT remove client
      (lock/share/delegation) state for x.

   The server generates the clientid and setclientid_confirm values and
   must take care to ensure that these values are extremely unlikely to
   ever be regenerated.

   ERRORS

      NFS4ERR_BADXDR
      NFS4ERR_CLID_INUSE
      NFS4ERR_INVAL
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT

14.2.34.  Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid

   SYNOPSIS

     clientid, verifier -> -

   ARGUMENT

     struct SETCLIENTID_CONFIRM4args {
             clientid4       clientid;
             verifier4       setclientid_confirm;
     };

   RESULT

     struct SETCLIENTID_CONFIRM4res {
             nfsstat4        status;
     };





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   DESCRIPTION

   This operation is used by the client to confirm the results from a
   previous call to SETCLIENTID.  The client provides the server
   supplied (from a SETCLIENTID response) clientid.  The server responds
   with a simple status of success or failure.

   IMPLEMENTATION

   The client must use the SETCLIENTID_CONFIRM operation to confirm the
   following two distinct cases:

   o  The client's use of a new shorthand client identifier (as returned
      from the server in the response to SETCLIENTID), a new callback
      value (as specified in the arguments to SETCLIENTID) and a new
      callback_ident (as specified in the arguments to SETCLIENTID)
      value.  The client's use of SETCLIENTID_CONFIRM in this case also
      confirms the removal of any of the client's previous relevant
      leased state. Relevant leased client state includes record locks,
      share reservations, and where the server does not support the
      CLAIM_DELEGATE_PREV claim type, delegations.  If the server
      supports CLAIM_DELEGATE_PREV, then SETCLIENTID_CONFIRM MUST NOT
      remove delegations for this client; relevant leased client state
      would then just include record locks and share reservations.

   o  The client's re-use of an old, previously confirmed, shorthand
      client identifier, a new callback value, and a new callback_ident
      value.  The client's use of SETCLIENTID_CONFIRM in this case MUST
      NOT result in the removal of any previous leased state (locks,
      share reservations, and delegations)

   We use the same notation and definitions for v, x, c, k, s, and
   unconfirmed and confirmed client records as introduced in the
   description of the SETCLIENTID operation. The arguments to
   SETCLIENTID_CONFIRM are indicated by the notation { c, s }, where c
   is a value of type clientid4, and s is a value of type verifier4
   corresponding to the setclientid_confirm field.

   As with SETCLIENTID, SETCLIENTID_CONFIRM is a non-idempotent
   operation, and we assume that the server is implementing the
   duplicate request cache (DRC).

   When the server gets a SETCLIENTID_CONFIRM { c, s } request, it
   processes it in the following manner.







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   o  It first looks up the request in the DRC. If there is a hit, it
      returns the result cached in the DRC.  The server does not remove
      any relevant leased client state nor does it modify any recorded
      callback and callback_ident information for client { x } as
      represented by the shorthand value c.

   For a DRC miss, the server checks for client records that match the
   shorthand value c.  The processing cases are as follows:

   o  The server has recorded an unconfirmed { v, x, c, k, s } record
      and a confirmed { v, x, c, l, t } record, such that s != t.  If
      the principals of the records do not match that of the
      SETCLIENTID_CONFIRM, the server returns NFS4ERR_CLID_INUSE, and no
      relevant leased client state is removed and no recorded callback
      and callback_ident information for client { x } is changed.
      Otherwise, the confirmed { v, x, c, l, t } record is removed and
      the unconfirmed { v, x, c, k, s } is marked as confirmed, thereby
      modifying recorded and confirmed callback and callback_ident
      information for client { x }.

      The server does not remove any relevant leased client state.

      The server returns NFS4_OK.

   o  The server has not recorded an unconfirmed { v, x, c, *, * } and
      has recorded a confirmed { v, x, c, *, s }. If the principals of
      the record and of SETCLIENTID_CONFIRM do not match, the server
      returns NFS4ERR_CLID_INUSE without removing any relevant leased
      client state and without changing recorded callback and
      callback_ident values for client { x }.

      If the principals match, then what has likely happened is that the
      client never got the response from the SETCLIENTID_CONFIRM, and
      the DRC entry has been purged. Whatever the scenario, since the
      principals match, as well as { c, s } matching a confirmed record,
      the server leaves client x's relevant leased client state intact,
      leaves its callback and callback_ident values unmodified, and
      returns NFS4_OK.

   o  The server has not recorded a confirmed { *, *, c, *, * }, and has
      recorded an unconfirmed { *, x, c, k, s }.  Even if this is a
      retry from client, nonetheless the client's first
      SETCLIENTID_CONFIRM attempt was not received by the server.  Retry
      or not, the server doesn't know, but it processes it as if were a
      first try.  If the principal of the unconfirmed { *, x, c, k, s }
      record mismatches that of the SETCLIENTID_CONFIRM request the
      server returns NFS4ERR_CLID_INUSE without removing any relevant
      leased client state.



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      Otherwise, the server records a confirmed { *, x, c, k, s }. If
      there is also a confirmed { *, x, d, *, t }, the server MUST
      remove the client x's relevant leased client state, and overwrite
      the callback state with k. The confirmed record { *, x, d, *, t }
      is removed.

      Server returns NFS4_OK.

   o  The server has no record of a confirmed or unconfirmed { *, *, c,
      *, s }.  The server returns NFS4ERR_STALE_CLIENTID.  The server
      does not remove any relevant leased client state, nor does it
      modify any recorded callback and callback_ident information for
      any client.

   The server needs to cache unconfirmed { v, x, c, k, s } client
   records and await for some time their confirmation.  As should be
   clear from the record processing discussions for SETCLIENTID and
   SETCLIENTID_CONFIRM, there are cases where the server does not
   deterministically remove unconfirmed client records.  To avoid
   running out of resources, the server is not required to hold
   unconfirmed records indefinitely.  One strategy the server might use
   is to set a limit on how many unconfirmed client records it will
   maintain, and then when the limit would be exceeded, remove the
   oldest record. Another strategy might be to remove an unconfirmed
   record when some amount of time has elapsed. The choice of the amount
   of time is fairly arbitrary but it is surely no higher than the
   server's lease time period. Consider that leases need to be renewed
   before the lease time expires via an operation from the client.  If
   the client cannot issue a SETCLIENTID_CONFIRM after a SETCLIENTID
   before a period of time equal to that of a lease expires, then the
   client is unlikely to be able maintain state on the server during
   steady state operation.

   If the client does send a SETCLIENTID_CONFIRM for an unconfirmed
   record that the server has already deleted, the client will get
   NFS4ERR_STALE_CLIENTID back.  If so, the client should then start
   over, and send SETCLIENTID to reestablish an unconfirmed client
   record and get back an unconfirmed clientid and setclientid_confirm
   verifier.  The client should then send the SETCLIENTID_CONFIRM to
   confirm the clientid.

   SETCLIENTID_CONFIRM does not establish or renew a lease.  However, if
   SETCLIENTID_CONFIRM removes relevant leased client state, and that
   state does not include existing delegations, the server MUST allow
   the client a period of time no less than the value of lease_time
   attribute, to reclaim, (via the CLAIM_DELEGATE_PREV claim type of the
   OPEN operation) its delegations before removing unreclaimed
   delegations.



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   ERRORS

      NFS4ERR_BADXDR
      NFS4ERR_CLID_INUSE
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE_CLIENTID

14.2.35.  Operation 37: VERIFY - Verify Same Attributes

   SYNOPSIS

     (cfh), fattr -> -

   ARGUMENT

     struct VERIFY4args {
             /* CURRENT_FH: object */
             fattr4          obj_attributes;
     };

   RESULT

     struct VERIFY4res {
             nfsstat4        status;
     };

   DESCRIPTION

   The VERIFY operation is used to verify that attributes have a value
   assumed by the client before proceeding with following operations in
   the compound request.  If any of the attributes do not match then the
   error NFS4ERR_NOT_SAME must be returned.  The current filehandle
   retains its value after successful completion of the operation.

   IMPLEMENTATION

   One possible use of the VERIFY operation is the following compound
   sequence.  With this the client is attempting to verify that the file
   being removed will match what the client expects to be removed.  This
   sequence can help prevent the unintended deletion of a file.

         PUTFH (directory filehandle)
         LOOKUP (file name)
         VERIFY (filehandle == fh)
         PUTFH (directory filehandle)
         REMOVE (file name)




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   This sequence does not prevent a second client from removing and
   creating a new file in the middle of this sequence but it does help
   avoid the unintended result.

   In the case that a recommended attribute is specified in the VERIFY
   operation and the server does not support that attribute for the
   filesystem object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.

   When the attribute rdattr_error or any write-only attribute (e.g.,
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ATTRNOTSUPP
      NFS4ERR_BADCHAR
      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_FHEXPIRED
      NFS4ERR_INVAL
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOT_SAME
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE

14.2.36.  Operation 38: WRITE - Write to File

   SYNOPSIS

     (cfh), stateid, offset, stable, data -> count, committed, writeverf

   ARGUMENT

     enum stable_how4 {
             UNSTABLE4       = 0,
             DATA_SYNC4      = 1,
             FILE_SYNC4      = 2
     };

     struct WRITE4args {
             /* CURRENT_FH: file */
             stateid4        stateid;
             offset4         offset;



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             stable_how4     stable;
             opaque          data<>;
     };

   RESULT

     struct WRITE4resok {
             count4          count;
             stable_how4     committed;
             verifier4       writeverf;
     };

     union WRITE4res switch (nfsstat4 status) {
      case NFS4_OK:
              WRITE4resok    resok4;
      default:
              void;
     };

   DESCRIPTION

   The WRITE operation is used to write data to a regular file.  The
   target file is specified by the current filehandle.  The offset
   specifies the offset where the data should be written.  An offset of
   0 (zero) specifies that the write should start at the beginning of
   the file.  The count, as encoded as part of the opaque data
   parameter, represents the number of bytes of data that are to be
   written.  If the count is 0 (zero), the WRITE will succeed and return
   a count of 0 (zero) subject to permissions checking.  The server may
   choose to write fewer bytes than requested by the client.

   Part of the write request is a specification of how the write is to
   be performed.  The client specifies with the stable parameter the
   method of how the data is to be processed by the server.  If stable
   is FILE_SYNC4, the server must commit the data written plus all
   filesystem metadata to stable storage before returning results.  This
   corresponds to the NFS version 2 protocol semantics.  Any other
   behavior constitutes a protocol violation.  If stable is DATA_SYNC4,
   then the server must commit all of the data to stable storage and
   enough of the metadata to retrieve the data before returning.  The
   server implementor is free to implement DATA_SYNC4 in the same
   fashion as FILE_SYNC4, but with a possible performance drop.  If
   stable is UNSTABLE4, the server is free to commit any part of the
   data and the metadata to stable storage, including all or none,
   before returning a reply to the client. There is no guarantee whether
   or when any uncommitted data will subsequently be committed to stable
   storage. The only guarantees made by the server are that it will not




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   destroy any data without changing the value of verf and that it will
   not commit the data and metadata at a level less than that requested
   by the client.

   The stateid value for a WRITE request represents a value returned
   from a previous record lock or share reservation request.  The
   stateid is used by the server to verify that the associated share
   reservation and any record locks are still valid and to update lease
   timeouts for the client.

   Upon successful completion, the following results are returned.  The
   count result is the number of bytes of data written to the file. The
   server may write fewer bytes than requested. If so, the actual number
   of bytes written starting at location, offset, is returned.

   The server also returns an indication of the level of commitment of
   the data and metadata via committed. If the server committed all data
   and metadata to stable storage, committed should be set to
   FILE_SYNC4. If the level of commitment was at least as strong as
   DATA_SYNC4, then committed should be set to DATA_SYNC4.  Otherwise,
   committed must be returned as UNSTABLE4. If stable was FILE4_SYNC,
   then committed must also be FILE_SYNC4: anything else constitutes a
   protocol violation. If stable was DATA_SYNC4, then committed may be
   FILE_SYNC4 or DATA_SYNC4: anything else constitutes a protocol
   violation. If stable was UNSTABLE4, then committed may be either
   FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.

   The final portion of the result is the write verifier.  The write
   verifier is a cookie that the client can use to determine whether the
   server has changed instance (boot) state between a call to WRITE and
   a subsequent call to either WRITE or COMMIT.  This cookie must be
   consistent during a single instance of the NFS version 4 protocol
   service and must be unique between instances of the NFS version 4
   protocol server, where uncommitted data may be lost.

   If a client writes data to the server with the stable argument set to
   UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
   UNSTABLE4, the client will follow up some time in the future with a
   COMMIT operation to synchronize outstanding asynchronous data and
   metadata with the server's stable storage, barring client error. It
   is possible that due to client crash or other error that a subsequent
   COMMIT will not be received by the server.

   For a WRITE with a stateid value of all bits 0, the server MAY allow
   the WRITE to be serviced subject to mandatory file locks or the
   current share deny modes for the file.  For a WRITE with a stateid





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   value of all bits 1, the server MUST NOT allow the WRITE operation to
   bypass locking checks at the server and are treated exactly the same
   as if a stateid of all bits 0 were used.

   On success, the current filehandle retains its value.

   IMPLEMENTATION

   It is possible for the server to write fewer bytes of data than
   requested by the client.  In this case, the server should not return
   an error unless no data was written at all.  If the server writes
   less than the number of bytes specified, the client should issue
   another WRITE to write the remaining data.

   It is assumed that the act of writing data to a file will cause the
   time_modified of the file to be updated.  However, the time_modified
   of the file should not be changed unless the contents of the file are
   changed.  Thus, a WRITE request with count set to 0 should not cause
   the time_modified of the file to be updated.

   The definition of stable storage has been historically a point of
   contention.  The following expected properties of stable storage may
   help in resolving design issues in the implementation. Stable storage
   is persistent storage that survives:

      1. Repeated power failures.
      2. Hardware failures (of any board, power supply, etc.).
      3. Repeated software crashes, including reboot cycle.

   This definition does not address failure of the stable storage module
   itself.

   The verifier is defined to allow a client to detect different
   instances of an NFS version 4 protocol server over which cached,
   uncommitted data may be lost. In the most likely case, the verifier
   allows the client to detect server reboots.  This information is
   required so that the client can safely determine whether the server
   could have lost cached data.  If the server fails unexpectedly and
   the client has uncommitted data from previous WRITE requests (done
   with the stable argument set to UNSTABLE4 and in which the result
   committed was returned as UNSTABLE4 as well) it may not have flushed
   cached data to stable storage. The burden of recovery is on the
   client and the client will need to retransmit the data to the server.

   A suggested verifier would be to use the time that the server was
   booted or the time the server was last started (if restarting the
   server without a reboot results in lost buffers).




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   The committed field in the results allows the client to do more
   effective caching.  If the server is committing all WRITE requests to
   stable storage, then it should return with committed set to
   FILE_SYNC4, regardless of the value of the stable field in the
   arguments. A server that uses an NVRAM accelerator may choose to
   implement this policy.  The client can use this to increase the
   effectiveness of the cache by discarding cached data that has already
   been committed on the server.

   Some implementations may return NFS4ERR_NOSPC instead of
   NFS4ERR_DQUOT when a user's quota is exceeded.  In the case that the
   current filehandle is a directory, the server will return
   NFS4ERR_ISDIR.  If the current filehandle is not a regular file or a
   directory, the server will return NFS4ERR_INVAL.

   If mandatory file locking is on for the file, and corresponding
   record of the data to be written file is read or write locked by an
   owner that is not associated with the stateid, the server will return
   NFS4ERR_LOCKED. If so, the client must check if the owner
   corresponding to the stateid used with the WRITE operation has a
   conflicting read lock that overlaps with the region that was to be
   written. If the stateid's owner has no conflicting read lock, then
   the client should try to get the appropriate write record lock via
   the LOCK operation before re-attempting the WRITE. When the WRITE
   completes, the client should release the record lock via LOCKU.

   If the stateid's owner had a conflicting read lock, then the client
   has no choice but to return an error to the application that
   attempted the WRITE. The reason is that since the stateid's owner had
   a read lock, the server either attempted to temporarily effectively
   upgrade this read lock to a write lock, or the server has no upgrade
   capability. If the server attempted to upgrade the read lock and
   failed, it is pointless for the client to re-attempt the upgrade via
   the LOCK operation, because there might be another client also trying
   to upgrade.  If two clients are blocked trying upgrade the same lock,
   the clients deadlock.  If the server has no upgrade capability, then
   it is pointless to try a LOCK operation to upgrade.

   ERRORS

      NFS4ERR_ACCESS
      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_DELAY
      NFS4ERR_DQUOT
      NFS4ERR_EXPIRED



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      NFS4ERR_FBIG
      NFS4ERR_FHEXPIRED
      NFS4ERR_GRACE
      NFS4ERR_INVAL
      NFS4ERR_IO
      NFS4ERR_ISDIR
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCKED
      NFS4ERR_MOVED
      NFS4ERR_NOFILEHANDLE
      NFS4ERR_NOSPC
      NFS4ERR_NXIO
      NFS4ERR_OLD_STATEID
      NFS4ERR_OPENMODE
      NFS4ERR_RESOURCE
      NFS4ERR_ROFS
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE
      NFS4ERR_STALE_STATEID

14.2.37.  Operation 39: RELEASE_LOCKOWNER - Release Lockowner State

   SYNOPSIS

     lockowner -> ()

   ARGUMENT

     struct RELEASE_LOCKOWNER4args {
             lock_owner4     lock_owner;
     };

   RESULT

     struct RELEASE_LOCKOWNER4res {
             nfsstat4        status;
     };

   DESCRIPTION

   This operation is used to notify the server that the lock_owner is no
   longer in use by the client.  This allows the server to release
   cached state related to the specified lock_owner.  If file locks,
   associated with the lock_owner, are held at the server, the error
   NFS4ERR_LOCKS_HELD will be returned and no further action will be
   taken.





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   IMPLEMENTATION

   The client may choose to use this operation to ease the amount of
   server state that is held.  Depending on behavior of applications at
   the client, it may be important for the client to use this operation
   since the server has certain obligations with respect to holding a
   reference to a lock_owner as long as the associated file is open.
   Therefore, if the client knows for certain that the lock_owner will
   no longer be used under the context of the associated open_owner4, it
   should use RELEASE_LOCKOWNER.

   ERRORS

      NFS4ERR_ADMIN_REVOKED
      NFS4ERR_BADXDR
      NFS4ERR_EXPIRED
      NFS4ERR_LEASE_MOVED
      NFS4ERR_LOCKS_HELD
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT
      NFS4ERR_STALE_CLIENTID

14.2.38.  Operation 10044: ILLEGAL - Illegal operation

   SYNOPSIS

     <null> -> ()

   ARGUMENT

             void;

   RESULT

             struct ILLEGAL4res {
                     nfsstat4        status;
             };

   DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the client sending an operation code within COMPOUND that is
   not supported. See the COMPOUND procedure description for more
   details.

   The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.





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   IMPLEMENTATION

   A client will probably not send an operation with code OP_ILLEGAL but
   if it does, the response will be ILLEGAL4res just as it would be with
   any other invalid operation code. Note that if the server gets an
   illegal operation code that is not OP_ILLEGAL, and if the server
   checks for legal operation codes during the XDR decode phase, then
   the ILLEGAL4res would not be returned.

   ERRORS

   NFS4ERR_OP_ILLEGAL

15.  NFS version 4 Callback Procedures

   The procedures used for callbacks are defined in the following
   sections.  In the interest of clarity, the terms "client" and
   "server" refer to NFS clients and servers, despite the fact that for
   an individual callback RPC, the sense of these terms would be
   precisely the opposite.

15.1.  Procedure 0: CB_NULL - No Operation

   SYNOPSIS

     <null>

   ARGUMENT

     void;

   RESULT

     void;

   DESCRIPTION

   Standard NULL procedure.  Void argument, void response.  Even though
   there is no direct functionality associated with this procedure, the
   server will use CB_NULL to confirm the existence of a path for RPCs
   from server to client.

   ERRORS

   None.






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15.2.  Procedure 1: CB_COMPOUND - Compound Operations

   SYNOPSIS

     compoundargs -> compoundres

   ARGUMENT

     enum nfs_cb_opnum4 {
             OP_CB_GETATTR           = 3,
             OP_CB_RECALL            = 4,
             OP_CB_ILLEGAL           = 10044
     };

     union nfs_cb_argop4 switch (unsigned argop) {
      case OP_CB_GETATTR:    CB_GETATTR4args opcbgetattr;
      case OP_CB_RECALL:     CB_RECALL4args  opcbrecall;
      case OP_CB_ILLEGAL:    void            opcbillegal;
     };

     struct CB_COMPOUND4args {
             utf8str_cs      tag;
             uint32_t        minorversion;
             uint32_t        callback_ident;
             nfs_cb_argop4   argarray<>;
     };

   RESULT

     union nfs_cb_resop4 switch (unsigned resop){
      case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
      case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;
     };

     struct CB_COMPOUND4res {
             nfsstat4 status;
             utf8str_cs      tag;
             nfs_cb_resop4   resarray<>;
     };

   DESCRIPTION

   The CB_COMPOUND procedure is used to combine one or more of the
   callback procedures into a single RPC request.  The main callback RPC
   program has two main procedures: CB_NULL and CB_COMPOUND.  All other
   operations use the CB_COMPOUND procedure as a wrapper.





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   In the processing of the CB_COMPOUND procedure, the client may find
   that it does not have the available resources to execute any or all
   of the operations within the CB_COMPOUND sequence.  In this case, the
   error NFS4ERR_RESOURCE will be returned for the particular operation
   within the CB_COMPOUND procedure where the resource exhaustion
   occurred.  This assumes that all previous operations within the
   CB_COMPOUND sequence have been evaluated successfully.

   Contained within the CB_COMPOUND results is a 'status' field.  This
   status must be equivalent to the status of the last operation that
   was executed within the CB_COMPOUND procedure.  Therefore, if an
   operation incurred an error then the 'status' value will be the same
   error value as is being returned for the operation that failed.

   For the definition of the "tag" field, see the section "Procedure 1:
   COMPOUND - Compound Operations".

   The value of callback_ident is supplied by the client during
   SETCLIENTID.  The server must use the client supplied callback_ident
   during the CB_COMPOUND to allow the client to properly identify the
   server.

   Illegal operation codes are handled in the same way as they are
   handled for the COMPOUND procedure.

   IMPLEMENTATION

   The CB_COMPOUND procedure is used to combine individual operations
   into a single RPC request.  The client interprets each of the
   operations in turn.  If an operation is executed by the client and
   the status of that operation is NFS4_OK, then the next operation in
   the CB_COMPOUND procedure is executed.  The client continues this
   process until there are no more operations to be executed or one of
   the operations has a status value other than NFS4_OK.

   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_OP_ILLEGAL
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT








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15.2.1.  Operation 3: CB_GETATTR - Get Attributes

   SYNOPSIS

     fh, attr_request -> attrmask, attr_vals

   ARGUMENT

     struct CB_GETATTR4args {
             nfs_fh4 fh;
             bitmap4 attr_request;
     };

   RESULT

     struct CB_GETATTR4resok {
             fattr4  obj_attributes;
     };

     union CB_GETATTR4res switch (nfsstat4 status) {
      case NFS4_OK:
              CB_GETATTR4resok       resok4;
      default:
              void;
     };

DESCRIPTION

   The CB_GETATTR operation is used by the server to obtain the
   current modified state of a file that has been write delegated.
   The attributes size and change are the only ones guaranteed to be
   serviced by the client.  See the section "Handling of CB_GETATTR"
   for a full description of how the client and server are to interact
   with the use of CB_GETATTR.

   If the filehandle specified is not one for which the client holds a
   write open delegation, an NFS4ERR_BADHANDLE error is returned.

   IMPLEMENTATION

   The client returns attrmask bits and the associated attribute
   values only for the change attribute, and attributes that it may
   change (time_modify, and size).








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   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_BADXDR
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT

15.2.2.  Operation 4: CB_RECALL - Recall an Open Delegation

   SYNOPSIS

     stateid, truncate, fh -> ()

   ARGUMENT

     struct CB_RECALL4args {
             stateid4        stateid;
             bool            truncate;
             nfs_fh4         fh;
     };

   RESULT

     struct CB_RECALL4res {
             nfsstat4        status;
     };

   DESCRIPTION

   The CB_RECALL operation is used to begin the process of recalling an
   open delegation and returning it to the server.

   The truncate flag is used to optimize recall for a file which is
   about to be truncated to zero.  When it is set, the client is freed
   of obligation to propagate modified data for the file to the server,
   since this data is irrelevant.

   If the handle specified is not one for which the client holds an open
   delegation, an NFS4ERR_BADHANDLE error is returned.

   If the stateid specified is not one corresponding to an open
   delegation for the file specified by the filehandle, an
   NFS4ERR_BAD_STATEID is returned.








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   IMPLEMENTATION

   The client should reply to the callback immediately.  Replying does
   not complete the recall except when an error was returned.  The
   recall is not complete until the delegation is returned using a
   DELEGRETURN.

   ERRORS

      NFS4ERR_BADHANDLE
      NFS4ERR_BAD_STATEID
      NFS4ERR_BADXDR
      NFS4ERR_RESOURCE
      NFS4ERR_SERVERFAULT

15.2.3.  Operation 10044: CB_ILLEGAL - Illegal Callback Operation

   SYNOPSIS

     <null> -> ()

   ARGUMENT

       void;

   RESULT

             struct CB_ILLEGAL4res {
                     nfsstat4        status;
             };

   DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the client sending an operation code within COMPOUND that is
   not supported. See the COMPOUND procedure description for more
   details.

   The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

   IMPLEMENTATION

   A server will probably not send an operation with code OP_CB_ILLEGAL
   but if it does, the response will be CB_ILLEGAL4res just as it would
   be with any other invalid operation code. Note that if the client






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   gets an illegal operation code that is not OP_ILLEGAL, and if the
   client checks for legal operation codes during the XDR decode phase,
   then the CB_ILLEGAL4res would not be returned.

   ERRORS

   NFS4ERR_OP_ILLEGAL

16.  Security Considerations

   NFS has historically used a model where, from an authentication
   perspective, the client was the entire machine, or at least the
   source IP address of the machine.  The NFS server relied on the NFS
   client to make the proper authentication of the end-user.  The NFS
   server in turn shared its files only to specific clients, as
   identified by the client's source IP address.  Given this model, the
   AUTH_SYS RPC security flavor simply identified the end-user using the
   client to the NFS server.  When processing NFS responses, the client
   ensured that the responses came from the same IP address and port
   number that the request was sent to.  While such a model is easy to
   implement and simple to deploy and use, it is certainly not a safe
   model.  Thus, NFSv4 mandates that implementations support a security
   model that uses end to end authentication, where an end-user on a
   client mutually authenticates (via cryptographic schemes that do not
   expose passwords or keys in the clear on the network) to a principal
   on an NFS server.  Consideration should also be given to the
   integrity and privacy of NFS requests and responses.  The issues of
   end to end mutual authentication, integrity, and privacy are
   discussed as part of the section on "RPC and Security Flavor".

   Note that while NFSv4 mandates an end to end mutual authentication
   model, the "classic" model of machine authentication via IP address
   checking and AUTH_SYS identification can still be supported with the
   caveat that the AUTH_SYS flavor is neither MANDATORY nor RECOMMENDED
   by this specification, and so interoperability via AUTH_SYS is not
   assured.

   For reasons of reduced administration overhead, better performance
   and/or reduction of CPU utilization, users of NFS version 4
   implementations may choose to not use security mechanisms that enable
   integrity protection on each remote procedure call and response. The
   use of mechanisms without integrity leaves the customer vulnerable to
   an attacker in between the NFS client and server that modifies the
   RPC request and/or the response. While implementations are free to
   provide the option to use weaker security mechanisms, there are two
   operations in particular that warrant the implementation overriding
   user choices.




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   The first such operation is SECINFO.  It is recommended that the
   client issue the SECINFO call such that it is protected with a
   security flavor that has integrity protection, such as RPCSEC_GSS
   with a security triple that uses either rpc_gss_svc_integrity or
   rpc_gss_svc_privacy (rpc_gss_svc_privacy includes integrity
   protection) service. Without integrity protection encapsulating
   SECINFO and therefore its results, an attacker in the middle could
   modify results such that the client might select a weaker algorithm
   in the set allowed by server, making the client and/or server
   vulnerable to further attacks.

   The second operation that should definitely use integrity protection
   is any GETATTR for the fs_locations attribute. The attack has two
   steps.  First the attacker modifies the unprotected results of some
   operation to return NFS4ERR_MOVED. Second, when the client follows up
   with a GETATTR for the fs_locations attribute, the attacker modifies
   the results to cause the client migrate its traffic to a server
   controlled by the attacker.

   Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are
   responsible for the release of client state, it is imperative that
   the principal used for these operations is checked against and match
   the previous use of these operations.  See the section "Client ID"
   for further discussion.

17.  IANA Considerations

17.1.  Named Attribute Definition

   The NFS version 4 protocol provides for the association of named
   attributes to files.  The name space identifiers for these attributes
   are defined as string names.  The protocol does not define the
   specific assignment of the name space for these file attributes.
   Even though the name space is not specifically controlled to prevent
   collisions, an IANA registry has been created for the registration of
   NFS version 4 named attributes.  Registration will be achieved
   through the publication of an Informational RFC and will require not
   only the name of the attribute but the syntax and semantics of the
   named attribute contents; the intent is to promote interoperability
   where common interests exist.  While application developers are
   allowed to define and use attributes as needed, they are encouraged
   to register the attributes with IANA.

17.2.  ONC RPC Network Identifiers (netids)

   The section "Structured Data Types" discussed the r_netid field and
   the corresponding r_addr field of a clientaddr4 structure.  The NFS
   version 4 protocol depends on the syntax and semantics of these



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   fields to effectively communicate callback information between client
   and server.  Therefore, an IANA registry has been created to include
   the values defined in this document and to allow for future expansion
   based on transport usage/availability.  Additions to this ONC RPC
   Network Identifier registry must be done with the publication of an
   RFC.

   The initial values for this registry are as follows (some of this
   text is replicated from section 2.2 for clarity):

   The Network Identifier (or r_netid for short) is used to specify a
   transport protocol and associated universal address (or r_addr for
   short).  The syntax of the Network Identifier is a US-ASCII string.
   The initial definitions for r_netid are:

      "tcp"   - TCP over IP version 4

      "udp"   - UDP over IP version 4

      "tcp6"  - TCP over IP version 6

      "udp6"  - UDP over IP version 6

   Note: the '"' marks are used for delimiting the strings for this
   document and are not part of the Network Identifier string.

   For the "tcp" and "udp" Network Identifiers the Universal Address or
   r_addr (for IPv4) is a US-ASCII string and is of the form:

   h1.h2.h3.h4.p1.p2

   The prefix, "h1.h2.h3.h4", is the standard textual form for
   representing an IPv4 address, which is always four octets long.
   Assuming big-endian ordering, h1, h2, h3, and h4, are respectively,
   the first through fourth octets each converted to ASCII-decimal.
   Assuming big-endian ordering, p1 and p2 are, respectively, the first
   and second octets each converted to ASCII-decimal.  For example, if a
   host, in big-endian order, has an address of 0x0A010307 and there is
   a service listening on, in big endian order, port 0x020F (decimal
   527), then complete universal address is "10.1.3.7.2.15".

   For the "tcp6" and "udp6" Network Identifiers the Universal Address
   or r_addr (for IPv6) is a US-ASCII string and is of the form:

      x1:x2:x3:x4:x5:x6:x7:x8.p1.p2






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RFC 3530                 NFS version 4 Protocol               April 2003


   The suffix "p1.p2" is the service port, and is computed the same way
   as with universal addresses for "tcp" and "udp".  The prefix,
   "x1:x2:x3:x4:x5:x6:x7:x8", is the standard textual form for
   representing an IPv6 address as defined in Section 2.2 of [RFC2373].
   Additionally, the two alternative forms specified in Section 2.2 of
   [RFC2373] are also acceptable.

   As mentioned, the registration of new Network Identifiers will
   require the publication of an Information RFC with similar detail as
   listed above for the Network Identifier itself and corresponding
   Universal Address.

18.  RPC definition file

   /*
    *  Copyright (C) The Internet Society (1998,1999,2000,2001,2002).
    *  All Rights Reserved.
    */

   /*
    *      nfs4_prot.x
    *
    */

   %#pragma ident  "%W%"

   /*
    * Basic typedefs for RFC 1832 data type definitions
    */
   typedef int             int32_t;
   typedef unsigned int    uint32_t;
   typedef hyper           int64_t;
   typedef unsigned hyper  uint64_t;

   /*
    * Sizes
    */
   const NFS4_FHSIZE               = 128;
   const NFS4_VERIFIER_SIZE        = 8;
   const NFS4_OPAQUE_LIMIT         = 1024;

   /*
    * File types
    */
   enum nfs_ftype4 {
           NF4REG          = 1,    /* Regular File */
           NF4DIR          = 2,    /* Directory */
           NF4BLK          = 3,    /* Special File - block device */



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RFC 3530                 NFS version 4 Protocol               April 2003


           NF4CHR          = 4,    /* Special File - character device */
           NF4LNK          = 5,    /* Symbolic Link */
           NF4SOCK         = 6,    /* Special File - socket */
           NF4FIFO         = 7,    /* Special File - fifo */
           NF4ATTRDIR      = 8,    /* Attribute Directory */
           NF4NAMEDATTR    = 9     /* Named Attribute */
   };

   /*
    * Error status
    */
   enum nfsstat4 {
           NFS4_OK                 = 0,    /* everything is okay      */
           NFS4ERR_PERM            = 1,    /* caller not privileged   */
           NFS4ERR_NOENT           = 2,    /* no such file/directory  */
           NFS4ERR_IO              = 5,    /* hard I/O error          */
           NFS4ERR_NXIO            = 6,    /* no such device          */
           NFS4ERR_ACCESS          = 13,   /* access denied           */
           NFS4ERR_EXIST           = 17,   /* file already exists     */
           NFS4ERR_XDEV            = 18,   /* different filesystems   */
           /* Unused/reserved        19 */
           NFS4ERR_NOTDIR          = 20,   /* should be a directory   */
           NFS4ERR_ISDIR           = 21,   /* should not be directory */
           NFS4ERR_INVAL           = 22,   /* invalid argument        */
           NFS4ERR_FBIG            = 27,   /* file exceeds server max */
           NFS4ERR_NOSPC           = 28,   /* no space on filesystem  */
           NFS4ERR_ROFS            = 30,   /* read-only filesystem    */
           NFS4ERR_MLINK           = 31,   /* too many hard links     */
           NFS4ERR_NAMETOOLONG     = 63,   /* name exceeds server max */
           NFS4ERR_NOTEMPTY        = 66,   /* directory not empty     */
           NFS4ERR_DQUOT           = 69,   /* hard quota limit reached*/
           NFS4ERR_STALE           = 70,   /* file no longer exists   */
           NFS4ERR_BADHANDLE       = 10001,/* Illegal filehandle      */
           NFS4ERR_BAD_COOKIE      = 10003,/* READDIR cookie is stale */
           NFS4ERR_NOTSUPP         = 10004,/* operation not supported */
           NFS4ERR_TOOSMALL        = 10005,/* response limit exceeded */
           NFS4ERR_SERVERFAULT     = 10006,/* undefined server error  */
           NFS4ERR_BADTYPE         = 10007,/* type invalid for CREATE */
           NFS4ERR_DELAY           = 10008,/* file "busy" - retry     */
           NFS4ERR_SAME            = 10009,/* nverify says attrs same */
           NFS4ERR_DENIED          = 10010,/* lock unavailable        */
           NFS4ERR_EXPIRED         = 10011,/* lock lease expired      */
           NFS4ERR_LOCKED          = 10012,/* I/O failed due to lock  */
           NFS4ERR_GRACE           = 10013,/* in grace period         */
           NFS4ERR_FHEXPIRED       = 10014,/* filehandle expired      */
           NFS4ERR_SHARE_DENIED    = 10015,/* share reserve denied    */
           NFS4ERR_WRONGSEC        = 10016,/* wrong security flavor   */
           NFS4ERR_CLID_INUSE      = 10017,/* clientid in use         */



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RFC 3530                 NFS version 4 Protocol               April 2003


           NFS4ERR_RESOURCE        = 10018,/* resource exhaustion     */
           NFS4ERR_MOVED           = 10019,/* filesystem relocated    */
           NFS4ERR_NOFILEHANDLE    = 10020,/* current FH is not set   */
           NFS4ERR_MINOR_VERS_MISMATCH = 10021,/* minor vers not supp */
           NFS4ERR_STALE_CLIENTID  = 10022,/* server has rebooted     */
           NFS4ERR_STALE_STATEID   = 10023,/* server has rebooted     */
           NFS4ERR_OLD_STATEID     = 10024,/* state is out of sync    */
           NFS4ERR_BAD_STATEID     = 10025,/* incorrect stateid       */
           NFS4ERR_BAD_SEQID       = 10026,/* request is out of seq.  */
           NFS4ERR_NOT_SAME        = 10027,/* verify - attrs not same */
           NFS4ERR_LOCK_RANGE      = 10028,/* lock range not supported*/
           NFS4ERR_SYMLINK         = 10029,/* should be file/directory*/
           NFS4ERR_RESTOREFH       = 10030,/* no saved filehandle     */
           NFS4ERR_LEASE_MOVED     = 10031,/* some filesystem moved   */
           NFS4ERR_ATTRNOTSUPP     = 10032,/* recommended attr not sup*/
           NFS4ERR_NO_GRACE        = 10033,/* reclaim outside of grace*/
           NFS4ERR_RECLAIM_BAD     = 10034,/* reclaim error at server */
           NFS4ERR_RECLAIM_CONFLICT = 10035,/* conflict on reclaim    */
           NFS4ERR_BADXDR          = 10036,/* XDR decode failed       */
           NFS4ERR_LOCKS_HELD      = 10037,/* file locks held at CLOSE*/
           NFS4ERR_OPENMODE        = 10038,/* conflict in OPEN and I/O*/
           NFS4ERR_BADOWNER        = 10039,/* owner translation bad   */
           NFS4ERR_BADCHAR         = 10040,/* utf-8 char not supported*/
           NFS4ERR_BADNAME         = 10041,/* name not supported      */
           NFS4ERR_BAD_RANGE       = 10042,/* lock range not supported*/
           NFS4ERR_LOCK_NOTSUPP    = 10043,/* no atomic up/downgrade  */
           NFS4ERR_OP_ILLEGAL      = 10044,/* undefined operation     */
           NFS4ERR_DEADLOCK        = 10045,/* file locking deadlock   */
           NFS4ERR_FILE_OPEN       = 10046,/* open file blocks op.    */
           NFS4ERR_ADMIN_REVOKED   = 10047,/* lockowner state revoked */
           NFS4ERR_CB_PATH_DOWN    = 10048 /* callback path down      */
   };

   /*
    * Basic data types
    */
   typedef uint32_t        bitmap4<>;
   typedef uint64_t        offset4;
   typedef uint32_t        count4;
   typedef uint64_t        length4;
   typedef uint64_t        clientid4;
   typedef uint32_t        seqid4;
   typedef opaque          utf8string<>;
   typedef utf8string      utf8str_cis;
   typedef utf8string      utf8str_cs;
   typedef utf8string      utf8str_mixed;
   typedef utf8str_cs      component4;
   typedef component4      pathname4<>;



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RFC 3530                 NFS version 4 Protocol               April 2003


   typedef uint64_t        nfs_lockid4;
   typedef uint64_t        nfs_cookie4;
   typedef utf8str_cs      linktext4;
   typedef opaque          sec_oid4<>;
   typedef uint32_t        qop4;
   typedef uint32_t        mode4;
   typedef uint64_t        changeid4;
   typedef opaque          verifier4[NFS4_VERIFIER_SIZE];

   /*
    * Timeval
    */
   struct nfstime4 {
           int64_t         seconds;
           uint32_t        nseconds;
   };

   enum time_how4 {
           SET_TO_SERVER_TIME4 = 0,
           SET_TO_CLIENT_TIME4 = 1
   };

   union settime4 switch (time_how4 set_it) {
    case SET_TO_CLIENT_TIME4:
            nfstime4       time;
    default:
            void;
   };

   /*
    * File access handle
    */
   typedef opaque  nfs_fh4<NFS4_FHSIZE>;


   /*
    * File attribute definitions
    */

   /*
    * FSID structure for major/minor
    */
   struct fsid4 {
           uint64_t        major;
           uint64_t        minor;
   };

   /*



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RFC 3530                 NFS version 4 Protocol               April 2003


    * Filesystem locations attribute for relocation/migration
    */
   struct fs_location4 {
           utf8str_cis     server<>;
           pathname4       rootpath;
   };

   struct fs_locations4 {
           pathname4       fs_root;
           fs_location4    locations<>;
   };

   /*
    * Various Access Control Entry definitions
    */

   /*
    * Mask that indicates which Access Control Entries are supported.
    * Values for the fattr4_aclsupport attribute.
    */
   const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
   const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
   const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
   const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;


   typedef uint32_t        acetype4;
   /*
    * acetype4 values, others can be added as needed.
    */
   const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
   const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
   const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
   const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;


   /*
    * ACE flag
    */
   typedef uint32_t aceflag4;

   /*
    * ACE flag values
    */
   const ACE4_FILE_INHERIT_ACE             = 0x00000001;
   const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
   const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
   const ACE4_INHERIT_ONLY_ACE             = 0x00000008;



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RFC 3530                 NFS version 4 Protocol               April 2003


   const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
   const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
   const ACE4_IDENTIFIER_GROUP             = 0x00000040;


   /*
    * ACE mask
    */
   typedef uint32_t        acemask4;

   /*
    * ACE mask values
    */
   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;

   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   /*
    * ACE4_GENERIC_READ -- defined as combination of
    *      ACE4_READ_ACL |
    *      ACE4_READ_DATA |
    *      ACE4_READ_ATTRIBUTES |
    *      ACE4_SYNCHRONIZE
    */

   const ACE4_GENERIC_READ = 0x00120081;

   /*
    * ACE4_GENERIC_WRITE -- defined as combination of
    *      ACE4_READ_ACL |
    *      ACE4_WRITE_DATA |
    *      ACE4_WRITE_ATTRIBUTES |
    *      ACE4_WRITE_ACL |



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RFC 3530                 NFS version 4 Protocol               April 2003


    *      ACE4_APPEND_DATA |
    *      ACE4_SYNCHRONIZE
    */
   const ACE4_GENERIC_WRITE = 0x00160106;


   /*
    * ACE4_GENERIC_EXECUTE -- defined as combination of
    *      ACE4_READ_ACL
    *      ACE4_READ_ATTRIBUTES
    *      ACE4_EXECUTE
    *      ACE4_SYNCHRONIZE
    */
   const ACE4_GENERIC_EXECUTE = 0x001200A0;


   /*
    * Access Control Entry definition
    */
   struct nfsace4 {
           acetype4        type;
           aceflag4        flag;
           acemask4        access_mask;
           utf8str_mixed   who;
   };

   /*
    * Field definitions for the fattr4_mode attribute
    */
   const MODE4_SUID = 0x800;  /* set user id on execution */
   const MODE4_SGID = 0x400;  /* set group id on execution */
   const MODE4_SVTX = 0x200;  /* save text even after use */
   const MODE4_RUSR = 0x100;  /* read permission: owner */
   const MODE4_WUSR = 0x080;  /* write permission: owner */
   const MODE4_XUSR = 0x040;  /* execute permission: owner */
   const MODE4_RGRP = 0x020;  /* read permission: group */
   const MODE4_WGRP = 0x010;  /* write permission: group */
   const MODE4_XGRP = 0x008;  /* execute permission: group */
   const MODE4_ROTH = 0x004;  /* read permission: other */
   const MODE4_WOTH = 0x002;  /* write permission: other */
   const MODE4_XOTH = 0x001;  /* execute permission: other */

   /*
    * Special data/attribute associated with
    * file types NF4BLK and NF4CHR.
    */
   struct specdata4 {
           uint32_t        specdata1;      /* major device number */



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RFC 3530                 NFS version 4 Protocol               April 2003


           uint32_t        specdata2;      /* minor device number */
   };

   /*
    * Values for fattr4_fh_expire_type
    */
   const   FH4_PERSISTENT          = 0x00000000;
   const   FH4_NOEXPIRE_WITH_OPEN  = 0x00000001;
   const   FH4_VOLATILE_ANY        = 0x00000002;
   const   FH4_VOL_MIGRATION       = 0x00000004;
   const   FH4_VOL_RENAME          = 0x00000008;


   typedef bitmap4         fattr4_supported_attrs;
   typedef nfs_ftype4      fattr4_type;
   typedef uint32_t        fattr4_fh_expire_type;
   typedef changeid4       fattr4_change;
   typedef uint64_t        fattr4_size;
   typedef bool            fattr4_link_support;
   typedef bool            fattr4_symlink_support;
   typedef bool            fattr4_named_attr;
   typedef fsid4           fattr4_fsid;
   typedef bool            fattr4_unique_handles;
   typedef uint32_t        fattr4_lease_time;
   typedef nfsstat4        fattr4_rdattr_error;

   typedef nfsace4         fattr4_acl<>;
   typedef uint32_t        fattr4_aclsupport;
   typedef bool            fattr4_archive;
   typedef bool            fattr4_cansettime;
   typedef bool            fattr4_case_insensitive;
   typedef bool            fattr4_case_preserving;
   typedef bool            fattr4_chown_restricted;
   typedef uint64_t        fattr4_fileid;
   typedef uint64_t        fattr4_files_avail;
   typedef nfs_fh4         fattr4_filehandle;
   typedef uint64_t        fattr4_files_free;
   typedef uint64_t        fattr4_files_total;
   typedef fs_locations4   fattr4_fs_locations;
   typedef bool            fattr4_hidden;
   typedef bool            fattr4_homogeneous;
   typedef uint64_t        fattr4_maxfilesize;
   typedef uint32_t        fattr4_maxlink;
   typedef uint32_t        fattr4_maxname;
   typedef uint64_t        fattr4_maxread;
   typedef uint64_t        fattr4_maxwrite;
   typedef utf8str_cs      fattr4_mimetype;
   typedef mode4           fattr4_mode;



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RFC 3530                 NFS version 4 Protocol               April 2003


   typedef uint64_t        fattr4_mounted_on_fileid;
   typedef bool            fattr4_no_trunc;
   typedef uint32_t        fattr4_numlinks;
   typedef utf8str_mixed   fattr4_owner;
   typedef utf8str_mixed   fattr4_owner_group;
   typedef uint64_t        fattr4_quota_avail_hard;
   typedef uint64_t        fattr4_quota_avail_soft;
   typedef uint64_t        fattr4_quota_used;
   typedef specdata4       fattr4_rawdev;
   typedef uint64_t        fattr4_space_avail;
   typedef uint64_t        fattr4_space_free;
   typedef uint64_t        fattr4_space_total;
   typedef uint64_t        fattr4_space_used;
   typedef bool            fattr4_system;
   typedef nfstime4        fattr4_time_access;
   typedef settime4        fattr4_time_access_set;
   typedef nfstime4        fattr4_time_backup;
   typedef nfstime4        fattr4_time_create;
   typedef nfstime4        fattr4_time_delta;
   typedef nfstime4        fattr4_time_metadata;
   typedef nfstime4        fattr4_time_modify;
   typedef settime4        fattr4_time_modify_set;


   /*
    * Mandatory Attributes
    */
   const FATTR4_SUPPORTED_ATTRS    = 0;
   const FATTR4_TYPE               = 1;
   const FATTR4_FH_EXPIRE_TYPE     = 2;
   const FATTR4_CHANGE             = 3;
   const FATTR4_SIZE               = 4;
   const FATTR4_LINK_SUPPORT       = 5;
   const FATTR4_SYMLINK_SUPPORT    = 6;
   const FATTR4_NAMED_ATTR         = 7;
   const FATTR4_FSID               = 8;
   const FATTR4_UNIQUE_HANDLES     = 9;
   const FATTR4_LEASE_TIME         = 10;
   const FATTR4_RDATTR_ERROR       = 11;
   const FATTR4_FILEHANDLE         = 19;

   /*
    * Recommended Attributes
    */
   const FATTR4_ACL                = 12;
   const FATTR4_ACLSUPPORT         = 13;
   const FATTR4_ARCHIVE            = 14;
   const FATTR4_CANSETTIME         = 15;



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RFC 3530                 NFS version 4 Protocol               April 2003


   const FATTR4_CASE_INSENSITIVE   = 16;
   const FATTR4_CASE_PRESERVING    = 17;
   const FATTR4_CHOWN_RESTRICTED   = 18;
   const FATTR4_FILEID             = 20;
   const FATTR4_FILES_AVAIL        = 21;
   const FATTR4_FILES_FREE         = 22;
   const FATTR4_FILES_TOTAL        = 23;
   const FATTR4_FS_LOCATIONS       = 24;
   const FATTR4_HIDDEN             = 25;
   const FATTR4_HOMOGENEOUS        = 26;
   const FATTR4_MAXFILESIZE        = 27;
   const FATTR4_MAXLINK            = 28;
   const FATTR4_MAXNAME            = 29;
   const FATTR4_MAXREAD            = 30;
   const FATTR4_MAXWRITE           = 31;
   const FATTR4_MIMETYPE           = 32;
   const FATTR4_MODE               = 33;
   const FATTR4_NO_TRUNC           = 34;
   const FATTR4_NUMLINKS           = 35;
   const FATTR4_OWNER              = 36;
   const FATTR4_OWNER_GROUP        = 37;
   const FATTR4_QUOTA_AVAIL_HARD   = 38;
   const FATTR4_QUOTA_AVAIL_SOFT   = 39;
   const FATTR4_QUOTA_USED         = 40;
   const FATTR4_RAWDEV             = 41;
   const FATTR4_SPACE_AVAIL        = 42;
   const FATTR4_SPACE_FREE         = 43;
   const FATTR4_SPACE_TOTAL        = 44;
   const FATTR4_SPACE_USED         = 45;
   const FATTR4_SYSTEM             = 46;
   const FATTR4_TIME_ACCESS        = 47;
   const FATTR4_TIME_ACCESS_SET    = 48;
   const FATTR4_TIME_BACKUP        = 49;
   const FATTR4_TIME_CREATE        = 50;
   const FATTR4_TIME_DELTA         = 51;
   const FATTR4_TIME_METADATA      = 52;
   const FATTR4_TIME_MODIFY        = 53;
   const FATTR4_TIME_MODIFY_SET    = 54;
   const FATTR4_MOUNTED_ON_FILEID  = 55;

   typedef opaque  attrlist4<>;

   /*
    * File attribute container
    */
   struct fattr4 {
           bitmap4         attrmask;
           attrlist4       attr_vals;



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RFC 3530                 NFS version 4 Protocol               April 2003


   };

   /*
    * Change info for the client
    */
   struct change_info4 {
           bool            atomic;
           changeid4       before;
           changeid4       after;
   };

   struct clientaddr4 {
           /* see struct rpcb in RFC 1833 */
           string r_netid<>;               /* network id */
           string r_addr<>;                /* universal address */
   };

   /*
    * Callback program info as provided by the client
    */
   struct cb_client4 {
           uint32_t        cb_program;
           clientaddr4     cb_location;
   };

   /*
    * Stateid
    */
   struct stateid4 {
           uint32_t        seqid;
           opaque          other[12];
   };

   /*
    * Client ID
    */
   struct nfs_client_id4 {
           verifier4       verifier;
           opaque          id<NFS4_OPAQUE_LIMIT>;
   };

   struct open_owner4 {
           clientid4       clientid;
           opaque          owner<NFS4_OPAQUE_LIMIT>;
   };

   struct lock_owner4 {
           clientid4       clientid;



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RFC 3530                 NFS version 4 Protocol               April 2003


           opaque          owner<NFS4_OPAQUE_LIMIT>;
   };

   enum nfs_lock_type4 {
           READ_LT         = 1,
           WRITE_LT        = 2,
           READW_LT        = 3,    /* blocking read */
           WRITEW_LT       = 4     /* blocking write */
   };

   /*
    * ACCESS: Check access permission
    */
   const ACCESS4_READ      = 0x00000001;
   const ACCESS4_LOOKUP    = 0x00000002;
   const ACCESS4_MODIFY    = 0x00000004;
   const ACCESS4_EXTEND    = 0x00000008;
   const ACCESS4_DELETE    = 0x00000010;
   const ACCESS4_EXECUTE   = 0x00000020;

   struct ACCESS4args {
           /* CURRENT_FH: object */
           uint32_t        access;
   };

   struct ACCESS4resok {
           uint32_t        supported;
           uint32_t        access;
   };

   union ACCESS4res switch (nfsstat4 status) {
    case NFS4_OK:
            ACCESS4resok   resok4;
    default:
            void;
   };

   /*
    * CLOSE: Close a file and release share reservations
    */
   struct CLOSE4args {
           /* CURRENT_FH: object */
           seqid4          seqid;
           stateid4        open_stateid;
   };

   union CLOSE4res switch (nfsstat4 status) {
    case NFS4_OK:



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RFC 3530                 NFS version 4 Protocol               April 2003


            stateid4       open_stateid;
    default:
            void;
   };

   /*
    * COMMIT: Commit cached data on server to stable storage
    */
   struct COMMIT4args {
           /* CURRENT_FH: file */
           offset4         offset;
           count4          count;
   };

   struct COMMIT4resok {
           verifier4       writeverf;
   };


   union COMMIT4res switch (nfsstat4 status) {
    case NFS4_OK:
            COMMIT4resok   resok4;
    default:
            void;
   };

   /*
    * CREATE: Create a non-regular file
    */
   union createtype4 switch (nfs_ftype4 type) {
    case NF4LNK:
            linktext4      linkdata;
    case NF4BLK:
    case NF4CHR:
            specdata4      devdata;
    case NF4SOCK:
    case NF4FIFO:
    case NF4DIR:
            void;
    default:
            void;          /* server should return NFS4ERR_BADTYPE */
   };

   struct CREATE4args {
           /* CURRENT_FH: directory for creation */
           createtype4     objtype;
           component4      objname;
           fattr4          createattrs;



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   };

   struct CREATE4resok {
           change_info4    cinfo;
           bitmap4         attrset;        /* attributes set */
   };

   union CREATE4res switch (nfsstat4 status) {
    case NFS4_OK:
            CREATE4resok resok4;
    default:
            void;
   };

   /*
    * DELEGPURGE: Purge Delegations Awaiting Recovery
    */
   struct DELEGPURGE4args {
           clientid4       clientid;
   };

   struct DELEGPURGE4res {
           nfsstat4        status;
   };

   /*
    * DELEGRETURN: Return a delegation
    */
   struct DELEGRETURN4args {
           /* CURRENT_FH: delegated file */
           stateid4        deleg_stateid;
   };

   struct DELEGRETURN4res {
           nfsstat4        status;
   };

   /*
    * GETATTR: Get file attributes
    */
   struct GETATTR4args {
           /* CURRENT_FH: directory or file */
           bitmap4         attr_request;
   };

   struct GETATTR4resok {
           fattr4          obj_attributes;
   };



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   union GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            GETATTR4resok  resok4;
    default:
            void;
   };

   /*
    * GETFH: Get current filehandle
    */
   struct GETFH4resok {
           nfs_fh4         object;
   };

   union GETFH4res switch (nfsstat4 status) {
    case NFS4_OK:
           GETFH4resok     resok4;
    default:
           void;
   };

   /*
    * LINK: Create link to an object
    */
   struct LINK4args {
           /* SAVED_FH: source object */
           /* CURRENT_FH: target directory */
           component4      newname;
   };

   struct LINK4resok {
           change_info4    cinfo;
   };

   union LINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LINK4resok resok4;
    default:
            void;
   };

   /*
    * For LOCK, transition from open_owner to new lock_owner
    */
   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;



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           lock_owner4     lock_owner;
   };

   /*
    * For LOCK, existing lock_owner continues to request file locks
    */
   struct exist_lock_owner4 {
           stateid4        lock_stateid;
           seqid4          lock_seqid;
   };

   union locker4 switch (bool new_lock_owner) {
    case TRUE:
           open_to_lock_owner4     open_owner;
    case FALSE:
           exist_lock_owner4       lock_owner;
   };

   /*
    * LOCK/LOCKT/LOCKU: Record lock management
    */
   struct LOCK4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           bool            reclaim;
           offset4         offset;
           length4         length;
           locker4         locker;
   };

   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };

   struct LOCK4resok {
           stateid4        lock_stateid;
   };

   union LOCK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LOCK4resok     resok4;
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    default:
            void;



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   };

   struct LOCKT4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           offset4         offset;
           length4         length;
           lock_owner4     owner;
   };

   union LOCKT4res switch (nfsstat4 status) {
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    case NFS4_OK:
            void;
    default:
            void;
   };

   struct LOCKU4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           seqid4          seqid;
           stateid4        lock_stateid;
           offset4         offset;
           length4         length;
   };

   union LOCKU4res switch (nfsstat4 status) {
    case   NFS4_OK:
            stateid4       lock_stateid;
    default:
            void;
   };

   /*
    * LOOKUP: Lookup filename
    */
   struct LOOKUP4args {
           /* CURRENT_FH: directory */
           component4      objname;
   };

   struct LOOKUP4res {
           /* CURRENT_FH: object */
           nfsstat4        status;
   };




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   /*
    * LOOKUPP: Lookup parent directory
    */
   struct LOOKUPP4res {
           /* CURRENT_FH: directory */
           nfsstat4        status;
   };

   /*
    * NVERIFY: Verify attributes different
    */
   struct NVERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };

   struct NVERIFY4res {
           nfsstat4        status;
   };

   /*
    * Various definitions for OPEN
    */
   enum createmode4 {
           UNCHECKED4      = 0,
           GUARDED4        = 1,
           EXCLUSIVE4      = 2
   };

   union createhow4 switch (createmode4 mode) {
    case UNCHECKED4:
    case GUARDED4:
            fattr4         createattrs;
    case EXCLUSIVE4:
            verifier4      createverf;
   };

   enum opentype4 {
           OPEN4_NOCREATE  = 0,
           OPEN4_CREATE    = 1
   };

   union openflag4 switch (opentype4 opentype) {
    case OPEN4_CREATE:
            createhow4     how;
    default:
            void;
   };



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   /* Next definitions used for OPEN delegation */
   enum limit_by4 {
           NFS_LIMIT_SIZE          = 1,
           NFS_LIMIT_BLOCKS        = 2
           /* others as needed */
   };

   struct nfs_modified_limit4 {
           uint32_t        num_blocks;
           uint32_t        bytes_per_block;
   };

   union nfs_space_limit4 switch (limit_by4 limitby) {
    /* limit specified as file size */
    case NFS_LIMIT_SIZE:
            uint64_t               filesize;
    /* limit specified by number of blocks */
    case NFS_LIMIT_BLOCKS:
            nfs_modified_limit4    mod_blocks;
   } ;

   /*
    * Share Access and Deny constants for open argument
    */
   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

   enum open_delegation_type4 {
           OPEN_DELEGATE_NONE      = 0,
           OPEN_DELEGATE_READ      = 1,
           OPEN_DELEGATE_WRITE     = 2
   };

   enum open_claim_type4 {
           CLAIM_NULL              = 0,
           CLAIM_PREVIOUS          = 1,
           CLAIM_DELEGATE_CUR      = 2,
           CLAIM_DELEGATE_PREV     = 3
   };

   struct open_claim_delegate_cur4 {
           stateid4        delegate_stateid;



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           component4      file;
   };

   union open_claim4 switch (open_claim_type4 claim) {
    /*
     * No special rights to file. Ordinary OPEN of the specified file.
     */
    case CLAIM_NULL:
           /* CURRENT_FH: directory */
           component4      file;

    /*
     * Right to the file established by an open previous to server
     * reboot.  File identified by filehandle obtained at that time
     * rather than by name.
     */
    case CLAIM_PREVIOUS:
           /* CURRENT_FH: file being reclaimed */
           open_delegation_type4   delegate_type;

    /*
     * Right to file based on a delegation granted by the server.
     * File is specified by name.
     */
    case CLAIM_DELEGATE_CUR:
           /* CURRENT_FH: directory */
           open_claim_delegate_cur4        delegate_cur_info;

    /* Right to file based on a delegation granted to a previous boot
     * instance of the client.  File is specified by name.
     */
    case CLAIM_DELEGATE_PREV:
            /* CURRENT_FH: directory */
           component4      file_delegate_prev;
   };

   /*
    * OPEN: Open a file, potentially receiving an open delegation
    */
   struct OPEN4args {
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
           open_owner4     owner;
           openflag4       openhow;
           open_claim4     claim;
   };




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   struct open_read_delegation4 {
           stateid4        stateid;        /* Stateid for delegation*/
           bool            recall;         /* Pre-recalled flag for
                                              delegations obtained
                                              by reclaim
                                              (CLAIM_PREVIOUS) */
           nfsace4         permissions;    /* Defines users who don't
                                              need an ACCESS call to
                                              open for read */
   };

   struct open_write_delegation4 {
           stateid4        stateid;        /* Stateid for delegation */
           bool            recall;         /* Pre-recalled flag for
                                              delegations obtained
                                              by reclaim
                                              (CLAIM_PREVIOUS) */
           nfs_space_limit4 space_limit;   /* Defines condition that
                                              the client must check to
                                              determine whether the
                                              file needs to be flushed
                                              to the server on close.
                                              */
           nfsace4         permissions;    /* Defines users who don't
                                              need an ACCESS call as
                                              part of a delegated
                                              open. */
   };

   union open_delegation4
   switch (open_delegation_type4 delegation_type) {
           case OPEN_DELEGATE_NONE:
                   void;
           case OPEN_DELEGATE_READ:
                   open_read_delegation4 read;
           case OPEN_DELEGATE_WRITE:
                   open_write_delegation4 write;
   };
   /*
    * Result flags
    */
   /* Client must confirm open */
   const OPEN4_RESULT_CONFIRM      = 0x00000002;
   /* Type of file locking behavior at the server */
   const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;

   struct OPEN4resok {
           stateid4        stateid;        /* Stateid for open */



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           change_info4    cinfo;          /* Directory Change Info */
           uint32_t        rflags;         /* Result flags */
           bitmap4         attrset;        /* attribute set for create*/
           open_delegation4 delegation;    /* Info on any open
                                              delegation */
   };

   union OPEN4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* CURRENT_FH: opened file */
           OPEN4resok      resok4;
    default:
           void;
   };

   /*
    * OPENATTR: open named attributes directory
    */
   struct OPENATTR4args {
           /* CURRENT_FH: object */
           bool    createdir;
   };

   struct OPENATTR4res {
           /* CURRENT_FH: named attr directory */
           nfsstat4        status;
   };

   /*
    * OPEN_CONFIRM: confirm the open
    */
   struct OPEN_CONFIRM4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
   };

   struct OPEN_CONFIRM4resok {
           stateid4        open_stateid;
   };

   union OPEN_CONFIRM4res switch (nfsstat4 status) {
       case NFS4_OK:
               OPEN_CONFIRM4resok     resok4;
    default:
            void;
   };




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   /*
    * OPEN_DOWNGRADE: downgrade the access/deny for a file
    */
   struct OPEN_DOWNGRADE4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
   };

   struct OPEN_DOWNGRADE4resok {
           stateid4        open_stateid;
   };

   union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
    case NFS4_OK:
           OPEN_DOWNGRADE4resok    resok4;
    default:
            void;
   };

   /*
    * PUTFH: Set current filehandle
    */
   struct PUTFH4args {
           nfs_fh4         object;
   };

   struct PUTFH4res {
           /* CURRENT_FH: */
           nfsstat4        status;
   };

   /*
    * PUTPUBFH: Set public filehandle
    */
   struct PUTPUBFH4res {
           /* CURRENT_FH: public fh */
           nfsstat4        status;
   };

   /*
    * PUTROOTFH: Set root filehandle
    */
   struct PUTROOTFH4res {

           /* CURRENT_FH: root fh */



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           nfsstat4        status;
   };

   /*
    * READ: Read from file
    */
   struct READ4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           count4          count;
   };

   struct READ4resok {
           bool            eof;
           opaque          data<>;
   };

   union READ4res switch (nfsstat4 status) {
    case NFS4_OK:
            READ4resok     resok4;
    default:
            void;
   };

   /*
    * READDIR: Read directory
    */
   struct READDIR4args {
           /* CURRENT_FH: directory */
           nfs_cookie4     cookie;
           verifier4       cookieverf;
           count4          dircount;
           count4          maxcount;
           bitmap4         attr_request;
   };

   struct entry4 {
           nfs_cookie4     cookie;
           component4      name;
           fattr4          attrs;
           entry4          *nextentry;
   };

   struct dirlist4 {
           entry4          *entries;
           bool            eof;
   };



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RFC 3530                 NFS version 4 Protocol               April 2003


   struct READDIR4resok {
           verifier4       cookieverf;
           dirlist4        reply;
   };


   union READDIR4res switch (nfsstat4 status) {
    case NFS4_OK:
            READDIR4resok  resok4;
    default:
            void;
   };


   /*
    * READLINK: Read symbolic link
    */
   struct READLINK4resok {
           linktext4       link;
   };

   union READLINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            READLINK4resok resok4;
    default:
            void;
   };

   /*
    * REMOVE: Remove filesystem object
    */
   struct REMOVE4args {
           /* CURRENT_FH: directory */
           component4      target;
   };

   struct REMOVE4resok {
           change_info4    cinfo;
   };

   union REMOVE4res switch (nfsstat4 status) {
    case NFS4_OK:
            REMOVE4resok   resok4;
    default:
            void;
   };

   /*



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RFC 3530                 NFS version 4 Protocol               April 2003


    * RENAME: Rename directory entry
    */
   struct RENAME4args {
           /* SAVED_FH: source directory */
           component4      oldname;
           /* CURRENT_FH: target directory */

           component4      newname;
   };

   struct RENAME4resok {
           change_info4    source_cinfo;
           change_info4    target_cinfo;
   };

   union RENAME4res switch (nfsstat4 status) {
    case NFS4_OK:
           RENAME4resok    resok4;
    default:
           void;
   };

   /*
    * RENEW: Renew a Lease
    */
   struct RENEW4args {
           clientid4       clientid;
   };

   struct RENEW4res {
           nfsstat4        status;
   };

   /*
    * RESTOREFH: Restore saved filehandle
    */

   struct RESTOREFH4res {
           /* CURRENT_FH: value of saved fh */
           nfsstat4        status;
   };

   /*
    * SAVEFH: Save current filehandle
    */
   struct SAVEFH4res {
           /* SAVED_FH: value of current fh */
           nfsstat4        status;



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   };

   /*
    * SECINFO: Obtain Available Security Mechanisms
    */
   struct SECINFO4args {
           /* CURRENT_FH: directory */
           component4      name;
   };

   /*

    * From RFC 2203
    */
   enum rpc_gss_svc_t {
           RPC_GSS_SVC_NONE        = 1,
           RPC_GSS_SVC_INTEGRITY   = 2,
           RPC_GSS_SVC_PRIVACY     = 3
   };

   struct rpcsec_gss_info {
           sec_oid4        oid;
           qop4            qop;
           rpc_gss_svc_t   service;
   };

   /* RPCSEC_GSS has a value of '6' - See RFC 2203 */
   union secinfo4 switch (uint32_t flavor) {
    case RPCSEC_GSS:
            rpcsec_gss_info        flavor_info;
    default:
            void;
   };

   typedef secinfo4 SECINFO4resok<>;

   union SECINFO4res switch (nfsstat4 status) {
    case NFS4_OK:
            SECINFO4resok resok4;
    default:
            void;
   };

   /*
    * SETATTR: Set attributes
    */
   struct SETATTR4args {
           /* CURRENT_FH: target object */



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           stateid4        stateid;
           fattr4          obj_attributes;
   };

   struct SETATTR4res {
           nfsstat4        status;
           bitmap4         attrsset;
   };

   /*
    * SETCLIENTID
    */
   struct SETCLIENTID4args {
           nfs_client_id4  client;
           cb_client4      callback;
           uint32_t        callback_ident;

   };

   struct SETCLIENTID4resok {
           clientid4       clientid;
           verifier4       setclientid_confirm;
   };

   union SETCLIENTID4res switch (nfsstat4 status) {
    case NFS4_OK:
            SETCLIENTID4resok      resok4;
    case NFS4ERR_CLID_INUSE:
            clientaddr4    client_using;
    default:
            void;
   };

   struct SETCLIENTID_CONFIRM4args {
           clientid4       clientid;
           verifier4       setclientid_confirm;
   };

   struct SETCLIENTID_CONFIRM4res {
           nfsstat4        status;
   };

   /*
    * VERIFY: Verify attributes same
    */
   struct VERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;



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   };

   struct VERIFY4res {
           nfsstat4        status;
   };

   /*
    * WRITE: Write to file
    */
   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
   };

   struct WRITE4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           stable_how4     stable;
           opaque          data<>;
   };

   struct WRITE4resok {
           count4          count;
           stable_how4     committed;
           verifier4       writeverf;
   };

   union WRITE4res switch (nfsstat4 status) {
    case NFS4_OK:
            WRITE4resok    resok4;
    default:
            void;
   };

   /*
    * RELEASE_LOCKOWNER: Notify server to release lockowner
    */
   struct RELEASE_LOCKOWNER4args {
           lock_owner4     lock_owner;
   };

   struct RELEASE_LOCKOWNER4res {
           nfsstat4        status;
   };

   /*



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RFC 3530                 NFS version 4 Protocol               April 2003


    * ILLEGAL: Response for illegal operation numbers
    */
   struct ILLEGAL4res {
           nfsstat4        status;
   };

   /*
    * Operation arrays
    */

   enum nfs_opnum4 {
           OP_ACCESS               = 3,
           OP_CLOSE                = 4,
           OP_COMMIT               = 5,
           OP_CREATE               = 6,
           OP_DELEGPURGE           = 7,
           OP_DELEGRETURN          = 8,
           OP_GETATTR              = 9,
           OP_GETFH                = 10,
           OP_LINK                 = 11,
           OP_LOCK                 = 12,
           OP_LOCKT                = 13,
           OP_LOCKU                = 14,
           OP_LOOKUP               = 15,
           OP_LOOKUPP              = 16,
           OP_NVERIFY              = 17,
           OP_OPEN                 = 18,
           OP_OPENATTR             = 19,
           OP_OPEN_CONFIRM         = 20,
           OP_OPEN_DOWNGRADE       = 21,
           OP_PUTFH                = 22,
           OP_PUTPUBFH             = 23,
           OP_PUTROOTFH            = 24,
           OP_READ                 = 25,
           OP_READDIR              = 26,
           OP_READLINK             = 27,
           OP_REMOVE               = 28,
           OP_RENAME               = 29,
           OP_RENEW                = 30,
           OP_RESTOREFH            = 31,
           OP_SAVEFH               = 32,
           OP_SECINFO              = 33,
           OP_SETATTR              = 34,
           OP_SETCLIENTID          = 35,
           OP_SETCLIENTID_CONFIRM  = 36,
           OP_VERIFY               = 37,
           OP_WRITE                = 38,
           OP_RELEASE_LOCKOWNER    = 39,



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           OP_ILLEGAL              = 10044
   };

   union nfs_argop4 switch (nfs_opnum4 argop) {
    case OP_ACCESS:        ACCESS4args opaccess;
    case OP_CLOSE:         CLOSE4args opclose;
    case OP_COMMIT:        COMMIT4args opcommit;
    case OP_CREATE:        CREATE4args opcreate;
    case OP_DELEGPURGE:    DELEGPURGE4args opdelegpurge;
    case OP_DELEGRETURN:   DELEGRETURN4args opdelegreturn;
    case OP_GETATTR:       GETATTR4args opgetattr;
    case OP_GETFH:         void;
    case OP_LINK:          LINK4args oplink;
    case OP_LOCK:          LOCK4args oplock;
    case OP_LOCKT:         LOCKT4args oplockt;
    case OP_LOCKU:         LOCKU4args oplocku;
    case OP_LOOKUP:        LOOKUP4args oplookup;
    case OP_LOOKUPP:       void;
    case OP_NVERIFY:       NVERIFY4args opnverify;
    case OP_OPEN:          OPEN4args opopen;
    case OP_OPENATTR:      OPENATTR4args opopenattr;
    case OP_OPEN_CONFIRM:  OPEN_CONFIRM4args opopen_confirm;
    case OP_OPEN_DOWNGRADE:        OPEN_DOWNGRADE4args opopen_downgrade;
    case OP_PUTFH:         PUTFH4args opputfh;
    case OP_PUTPUBFH:      void;
    case OP_PUTROOTFH:     void;
    case OP_READ:          READ4args opread;
    case OP_READDIR:       READDIR4args opreaddir;
    case OP_READLINK:      void;
    case OP_REMOVE:        REMOVE4args opremove;
    case OP_RENAME:        RENAME4args oprename;
    case OP_RENEW:         RENEW4args oprenew;
    case OP_RESTOREFH:     void;
    case OP_SAVEFH:        void;
    case OP_SECINFO:       SECINFO4args opsecinfo;
    case OP_SETATTR:       SETATTR4args opsetattr;
    case OP_SETCLIENTID:   SETCLIENTID4args opsetclientid;
    case OP_SETCLIENTID_CONFIRM:   SETCLIENTID_CONFIRM4args
                                           opsetclientid_confirm;
    case OP_VERIFY:        VERIFY4args opverify;
    case OP_WRITE:         WRITE4args opwrite;
    case OP_RELEASE_LOCKOWNER:     RELEASE_LOCKOWNER4args
                                       oprelease_lockowner;
    case OP_ILLEGAL:       void;
   };

   union nfs_resop4 switch (nfs_opnum4 resop){
    case OP_ACCESS:        ACCESS4res opaccess;



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RFC 3530                 NFS version 4 Protocol               April 2003


    case OP_CLOSE:         CLOSE4res opclose;
    case OP_COMMIT:        COMMIT4res opcommit;
    case OP_CREATE:        CREATE4res opcreate;
    case OP_DELEGPURGE:    DELEGPURGE4res opdelegpurge;
    case OP_DELEGRETURN:   DELEGRETURN4res opdelegreturn;
    case OP_GETATTR:       GETATTR4res opgetattr;
    case OP_GETFH:         GETFH4res opgetfh;
    case OP_LINK:          LINK4res oplink;
    case OP_LOCK:          LOCK4res oplock;
    case OP_LOCKT:         LOCKT4res oplockt;
    case OP_LOCKU:         LOCKU4res oplocku;
    case OP_LOOKUP:        LOOKUP4res oplookup;
    case OP_LOOKUPP:       LOOKUPP4res oplookupp;
    case OP_NVERIFY:       NVERIFY4res opnverify;
    case OP_OPEN:          OPEN4res opopen;
    case OP_OPENATTR:      OPENATTR4res opopenattr;
    case OP_OPEN_CONFIRM:  OPEN_CONFIRM4res opopen_confirm;
    case OP_OPEN_DOWNGRADE:        OPEN_DOWNGRADE4res opopen_downgrade;
    case OP_PUTFH:         PUTFH4res opputfh;
    case OP_PUTPUBFH:      PUTPUBFH4res opputpubfh;
    case OP_PUTROOTFH:     PUTROOTFH4res opputrootfh;
    case OP_READ:          READ4res opread;
    case OP_READDIR:       READDIR4res opreaddir;
    case OP_READLINK:      READLINK4res opreadlink;
    case OP_REMOVE:        REMOVE4res opremove;
    case OP_RENAME:        RENAME4res oprename;
    case OP_RENEW:         RENEW4res oprenew;
    case OP_RESTOREFH:     RESTOREFH4res oprestorefh;
    case OP_SAVEFH:        SAVEFH4res opsavefh;
    case OP_SECINFO:       SECINFO4res opsecinfo;
    case OP_SETATTR:       SETATTR4res opsetattr;
    case OP_SETCLIENTID:   SETCLIENTID4res opsetclientid;
    case OP_SETCLIENTID_CONFIRM:   SETCLIENTID_CONFIRM4res
                                           opsetclientid_confirm;
    case OP_VERIFY:        VERIFY4res opverify;
    case OP_WRITE:         WRITE4res opwrite;
    case OP_RELEASE_LOCKOWNER:     RELEASE_LOCKOWNER4res
                                       oprelease_lockowner;
    case OP_ILLEGAL:       ILLEGAL4res opillegal;
   };

   struct COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           nfs_argop4      argarray<>;
   };

   struct COMPOUND4res {



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           nfsstat4 status;
           utf8str_cs      tag;
           nfs_resop4      resarray<>;
   };

   /*
    * Remote file service routines
    */
   program NFS4_PROGRAM {
           version NFS_V4 {
                   void
                           NFSPROC4_NULL(void) = 0;

                   COMPOUND4res
                           NFSPROC4_COMPOUND(COMPOUND4args) = 1;

           } = 4;
   } = 100003;



   /*
    * NFS4 Callback Procedure Definitions and Program
    */

   /*
    * CB_GETATTR: Get Current Attributes
    */
   struct CB_GETATTR4args {
           nfs_fh4 fh;
           bitmap4 attr_request;
   };

   struct CB_GETATTR4resok {
           fattr4  obj_attributes;
   };

   union CB_GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            CB_GETATTR4resok       resok4;
    default:
            void;
   };

   /*
    * CB_RECALL: Recall an Open Delegation
    */
   struct CB_RECALL4args {



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           stateid4        stateid;
           bool            truncate;
           nfs_fh4         fh;
   };

   struct CB_RECALL4res {
           nfsstat4        status;
   };

   /*
    * CB_ILLEGAL: Response for illegal operation numbers
    */
   struct CB_ILLEGAL4res {
           nfsstat4        status;
   };

   /*
    * Various definitions for CB_COMPOUND
    */
   enum nfs_cb_opnum4 {
           OP_CB_GETATTR           = 3,
           OP_CB_RECALL            = 4,
           OP_CB_ILLEGAL           = 10044
   };

   union nfs_cb_argop4 switch (unsigned argop) {
    case OP_CB_GETATTR:    CB_GETATTR4args opcbgetattr;
    case OP_CB_RECALL:     CB_RECALL4args  opcbrecall;
    case OP_CB_ILLEGAL:    void;
   };

   union nfs_cb_resop4 switch (unsigned resop){
    case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
    case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;
    case OP_CB_ILLEGAL:    CB_ILLEGAL4res  opcbillegal;
   };

   struct CB_COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           uint32_t        callback_ident;
           nfs_cb_argop4   argarray<>;
   };

   struct CB_COMPOUND4res {
           nfsstat4 status;
           utf8str_cs      tag;
           nfs_cb_resop4   resarray<>;



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   };


   /*
    * Program number is in the transient range since the client
    * will assign the exact transient program number and provide
    * that to the server via the SETCLIENTID operation.
    */
   program NFS4_CALLBACK {
           version NFS_CB {
                   void
                           CB_NULL(void) = 0;
                   CB_COMPOUND4res
                           CB_COMPOUND(CB_COMPOUND4args) = 1;
           } = 1;
   } = 0x40000000;

19.  Acknowledgements

   The authors thank and acknowledge:

   Neil Brown for his extensive review and comments of various
   documents. Rick Macklem at the University of Guelph, Mike Frisch,
   Sergey Klyushin, and Dan Trufasiu of Hummingbird Ltd., and Andy
   Adamson, Bruce Fields, Jim Rees, and Kendrick Smith from the CITI
   organization at the University of Michigan, for their implementation
   efforts and feedback on the protocol specification. Mike Kupfer for
   his review of the file locking and ACL mechanisms.  Alan Yoder for
   his input to ACL mechanisms. Peter Astrand for his close review of
   the protocol specification. Ran Atkinson for his constant reminder
   that users do matter.

20.  Normative References

   [ISO10646]                "ISO/IEC 10646-1:1993. International
                             Standard -- Information technology --
                             Universal Multiple-Octet Coded Character
                             Set (UCS) -- Part 1: Architecture and Basic
                             Multilingual Plane."

   [RFC793]                  Postel, J., "Transmission Control
                             Protocol", STD 7, RFC 793, September 1981.

   [RFC1831]                 Srinivasan, R., "RPC: Remote Procedure Call
                             Protocol Specification Version 2", RFC
                             1831, August 1995.





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   [RFC1832]                 Srinivasan, R., "XDR: External Data
                             Representation Standard", RFC 1832, August
                             1995.

   [RFC2373]                 Hinden, R. and S. Deering, "IP Version 6
                             Addressing Architecture", RFC 2373, July
                             1998.

   [RFC1964]                 Linn, J., "The Kerberos Version 5 GSS-API
                             Mechanism", RFC 1964, June 1996.

   [RFC2025]                 Adams, C., "The Simple Public-Key GSS-API
                             Mechanism (SPKM)", RFC 2025, October 1996.

   [RFC2119]                 Bradner, S., "Key words for use in RFCs to
                             Indicate Requirement Levels", BCP 14, RFC
                             2119, March 1997.

   [RFC2203]                 Eisler, M., Chiu, A. and L. Ling,
                             "RPCSEC_GSS Protocol Specification", RFC
                             2203, September 1997.

   [RFC2277]                 Alvestrand, H., "IETF Policy on Character
                             Sets and Languages", BCP 19, RFC 2277,
                             January 1998.

   [RFC2279]                 Yergeau, F., "UTF-8, a transformation
                             format of ISO 10646", RFC 2279, January
                             1998.

   [RFC2623]                 Eisler, M., "NFS Version 2 and Version 3
                             Security Issues and the NFS Protocol's Use
                             of RPCSEC_GSS and Kerberos V5", RFC 2623,
                             June 1999.

   [RFC2743]                 Linn, J., "Generic Security Service
                             Application Program Interface, Version 2,
                             Update 1", RFC 2743, January 2000.

   [RFC2847]                 Eisler, M., "LIPKEY - A Low Infrastructure
                             Public Key Mechanism Using SPKM", RFC 2847,
                             June 2000.

   [RFC3010]                 Shepler, S., Callaghan, B., Robinson, D.,
                             Thurlow, R., Beame, C., Eisler, M. and D.
                             Noveck, "NFS version 4 Protocol", RFC 3010,
                             December 2000.




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   [RFC3454]                 Hoffman, P. and P. Blanchet, "Preparation
                             of Internationalized Strings
                             ("stringprep")", RFC 3454, December 2002.

   [Unicode1]                The Unicode Consortium, "The Unicode
                             Standard, Version 3.0", Addison-Wesley
                             Developers Press, Reading, MA, 2000. ISBN
                             0-201-61633-5.

                             More information available at:
                             http://www.unicode.org/

   [Unicode2]                "Unsupported Scripts" Unicode, Inc., The
                             Unicode Consortium, P.O. Box 700519, San
                             Jose, CA 95710-0519 USA, September 1999.
                             http://www.unicode.org/unicode/standard/
                             unsupported.html

21.  Informative References

   [Floyd]                   S. Floyd, V. Jacobson, "The Synchronization
                             of Periodic Routing Messages," IEEE/ACM
                             Transactions on Networking, 2(2), pp. 122-
                             136, April 1994.

   [Gray]                    C. Gray, D. Cheriton, "Leases: An Efficient
                             Fault-Tolerant Mechanism for Distributed
                             File Cache Consistency," Proceedings of the
                             Twelfth Symposium on Operating Systems
                             Principles, p. 202-210, December 1989.

   [Juszczak]                Juszczak, Chet, "Improving the Performance
                             and Correctness of an NFS Server," USENIX
                             Conference Proceedings, USENIX Association,
                             Berkeley, CA, June 1990, pages 53-63.
                             Describes reply cache implementation that
                             avoids work in the server by handling
                             duplicate requests. More important, though
                             listed as a side-effect, the reply cache
                             aids in the avoidance of destructive non-
                             idempotent operation re-application --
                             improving correctness.









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   [Kazar]                   Kazar, Michael Leon, "Synchronization and
                             Caching Issues in the Andrew File System,"
                             USENIX Conference Proceedings, USENIX
                             Association, Berkeley, CA, Dallas Winter
                             1988, pages 27-36.  A description of the
                             cache consistency scheme in AFS.
                             Contrasted with other distributed file
                             systems.

   [Macklem]                 Macklem, Rick, "Lessons Learned Tuning the
                             4.3BSD Reno Implementation of the NFS
                             Protocol," Winter USENIX Conference
                             Proceedings, USENIX Association, Berkeley,
                             CA, January 1991.  Describes performance
                             work in tuning the 4.3BSD Reno NFS
                             implementation. Describes performance
                             improvement (reduced CPU loading) through
                             elimination of data copies.

   [Mogul]                   Mogul, Jeffrey C., "A Recovery Protocol for
                             Spritely NFS," USENIX File System Workshop
                             Proceedings, Ann Arbor, MI, USENIX
                             Association, Berkeley, CA, May 1992.
                             Second paper on Spritely NFS proposes a
                             lease-based scheme for recovering state of
                             consistency protocol.

   [Nowicki]                 Nowicki, Bill, "Transport Issues in the
                             Network File System," ACM SIGCOMM
                             newsletter Computer Communication Review,
                             April 1989.  A brief description of the
                             basis for the dynamic retransmission work.

   [Pawlowski]               Pawlowski, Brian, Ron Hixon, Mark Stein,
                             Joseph Tumminaro, "Network Computing in the
                             UNIX and IBM Mainframe Environment,"
                             Uniforum `89 Conf.  Proc., (1989)
                             Description of an NFS server implementation
                             for IBM's MVS operating system.

   [RFC1094]                 Sun Microsystems, Inc., "NFS: Network File
                             System Protocol Specification", RFC 1094,
                             March 1989.

   [RFC1345]                 Simonsen, K., "Character Mnemonics &
                             Character Sets", RFC 1345, June 1992.





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   [RFC1813]                 Callaghan, B., Pawlowski, B. and P.
                             Staubach, "NFS Version 3 Protocol
                             Specification", RFC 1813, June 1995.

   [RFC3232]                 Reynolds, J., Editor, "Assigned Numbers:
                             RFC 1700 is Replaced by an On-line
                             Database", RFC 3232, January 2002.

   [RFC1833]                 Srinivasan, R., "Binding Protocols for ONC
                             RPC Version 2", RFC 1833, August 1995.

   [RFC2054]                 Callaghan, B., "WebNFS Client
                             Specification", RFC 2054, October 1996.

   [RFC2055]                 Callaghan, B., "WebNFS Server
                             Specification", RFC 2055,  October 1996.

   [RFC2152]                 Goldsmith, D. and M. Davis, "UTF-7 A Mail-
                             Safe Transformation Format of Unicode", RFC
                             2152, May 1997.

   [RFC2224]                 Callaghan, B., "NFS URL Scheme", RFC 2224,
                             October 1997.

   [RFC2624]                 Shepler, S., "NFS Version 4 Design
                             Considerations", RFC 2624, June 1999.

   [RFC2755]                 Chiu, A., Eisler, M. and B. Callaghan,
                             "Security Negotiation for WebNFS" , RFC
                             2755, June 2000.

   [Sandberg]                Sandberg, R., D. Goldberg, S. Kleiman, D.
                             Walsh, B.  Lyon, "Design and Implementation
                             of the Sun Network Filesystem," USENIX
                             Conference Proceedings, USENIX Association,
                             Berkeley, CA, Summer 1985.  The basic paper
                             describing the SunOS implementation of the
                             NFS version 2 protocol, and discusses the
                             goals, protocol specification and trade-
                             offs.











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   [Srinivasan]              Srinivasan, V., Jeffrey C. Mogul, "Spritely
                             NFS: Implementation and Performance of
                             Cache Consistency Protocols", WRL Research
                             Report 89/5, Digital Equipment Corporation
                             Western Research Laboratory, 100 Hamilton
                             Ave., Palo Alto, CA, 94301, May 1989.  This
                             paper analyzes the effect of applying a
                             Sprite-like consistency protocol applied to
                             standard NFS. The issues of recovery in a
                             stateful environment are covered in
                             [Mogul].

   [XNFS]                    The Open Group, Protocols for Interworking:
                             XNFS, Version 3W, The Open Group, 1010 El
                             Camino Real Suite 380, Menlo Park, CA
                             94025, ISBN 1-85912-184-5, February 1998.

                             HTML version available:
                             http://www.opengroup.org

22.  Authors' Information

22.1.  Editor's Address

   Spencer Shepler
   Sun Microsystems, Inc.
   7808 Moonflower Drive
   Austin, Texas  78750

   Phone: +1 512-349-9376
   EMail: spencer.shepler@sun.com




















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22.2.  Authors' Addresses

   Carl Beame
   Hummingbird Ltd.

   EMail: beame@bws.com

   Brent Callaghan
   Sun Microsystems, Inc.
   17 Network Circle
   Menlo Park, CA  94025

   Phone: +1 650-786-5067
   EMail: brent.callaghan@sun.com

   Mike Eisler
   5765 Chase Point Circle
   Colorado Springs, CO  80919

   Phone: +1 719-599-9026
   EMail: mike@eisler.com

   David Noveck
   Network Appliance
   375 Totten Pond Road
   Waltham, MA  02451

   Phone: +1 781-768-5347
   EMail: dnoveck@netapp.com

   David Robinson
   Sun Microsystems, Inc.
   5300 Riata Park Court
   Austin, TX  78727

   Phone: +1 650-786-5088
   EMail: david.robinson@sun.com

   Robert Thurlow
   Sun Microsystems, Inc.
   500 Eldorado Blvd.
   Broomfield, CO  80021

   Phone: +1 650-786-5096
   EMail: robert.thurlow@sun.com






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23.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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