Move functions to their own files

Also we move the source code to a src/ directory.  We also move from
using `struct luxdisp` to `lux_t` to signify that we don’t want the user
to be messing with the struct members.

15 files changed, 468 insertions, 224 deletions

diff --git a/liblux.c b/liblux.c
deleted file mode 100644
index 8061eec..0000000
--- a/liblux.c
+++ /dev/null
@@ -1,208 +0,0 @@
-/*
- * BSD Zero Clause License
- *
- * Copyright (c) 2022 Thomas Voss
- *
- * Permission to use, copy, modify, and/or distribute this software for any
- * purpose with or without fee is hereby granted.
- *
- * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
- * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
- * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
- * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
- * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
- * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
- * PERFORMANCE OF THIS SOFTWARE.
- */
-
-#define _POSIX_C_SOURCE 200809L
-
-#include <sys/types.h>
-
-#include <dirent.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <unistd.h>
-
-#include "lux.h"
-
-#ifdef O_PATH
-	#define GETDIR_FLAGS O_PATH
-#else
-	#define GETDIR_FLAGS (O_RDONLY | O_DIRECTORY)
-#endif
-
-static int intlen(int);
-static int getdir(void);
-static FILE *getbstream(int);
-
-void
-luxfree(struct luxdisp *disp)
-{
-	if (disp->__dirfd != -1)
-		close(disp->__dirfd);
-	if (disp->__bstream != NULL)
-		fclose(disp->__bstream);
-}
-
-int
-luxinit(struct luxdisp *disp)
-{
-	/* Set the default values for the luxdisp struct.  We want to be as lazy
-	 * as possible, so we don't bother with __bstream and __max yet.  We do
-	 * need __dirfd though.
-	 */
-	*disp = (struct luxdisp) {
-		.__bstream = NULL,
-		.__max     = -1,
-		.__dirfd   = getdir()
-	};
-	return disp->__dirfd;
-}
-
-int
-luxmax(struct luxdisp *disp)
-{
-	/* The maximum brightness shouldn't change, so we can cache it in the
-	 * struct.
-	 */
-	if (disp->__max != -1)
-		return disp->__max;
-
-	int fd = openat(disp->__dirfd, "max_brightness", O_RDONLY);
-	if (fd == -1)
-		return -1;
-	FILE *stream = fdopen(fd, "r");
-	if (stream == NULL) {
-		close(fd);
-		return -1;
-	}
-
-	fscanf(stream, "%d", &disp->__max);
-	fclose(stream);
-	return disp->__max;
-}
-
-int
-luxget(struct luxdisp *disp)
-{
-	/* If we don't have an open stream with the brightness file yet then
-	 * open one.  If we do, we instead rewind to the start of the file so
-	 * that we don't just read an EOF.
-	 */
-	if (disp->__bstream == NULL) {
-		if ((disp->__bstream = getbstream(disp->__dirfd)) == NULL)
-			return -1;
-	} else
-		rewind(disp->__bstream);
-
-	int n;
-	fscanf(disp->__bstream, "%d", &n);
-	return n;
-}
-
-int
-luxset(struct luxdisp *disp, int n)
-{
-	/* The same deal as in luxget() */
-	if (disp->__bstream == NULL) {
-		if ((disp->__bstream = getbstream(disp->__dirfd)) == NULL)
-			return -1;
-	} else
-		rewind(disp->__bstream);
-
-	/* After writing the new brightness value to the brightness file, we
-	 * need to truncate it so that luxset(disp, 1234); luxset(disp, 9);
-	 * gives us a final brightness of 2 and not 9234.
-	 */
-	fprintf(disp->__bstream, "%d", n);
-	ftruncate(fileno(disp->__bstream), intlen(n));
-	return n;
-}
-
-int
-luxinc(struct luxdisp *disp, int n)
-{
-	return luxset(disp, luxget(disp) + n);
-}
-
-int
-luxdec(struct luxdisp *disp, int n)
-{
-	return luxinc(disp, -n);
-}
-
-double
-luxgetp(struct luxdisp *disp)
-{
-	int cur, max;
-	if ((cur = luxget(disp)) == -1 || (max = luxmax(disp)) == -1)
-		return -1;
-	return (double) cur / max * 100;
-}
-
-double
-luxsetp(struct luxdisp *disp, double p)
-{
-	int max = luxmax(disp);
-	return max == -1 ? -1 : luxset(disp, (int) (p / 100 * max));
-}
-
-double
-luxincp(struct luxdisp *disp, double p)
-{
-	return luxsetp(disp, luxgetp(disp) + p);
-}
-
-double
-luxdecp(struct luxdisp *disp, double p)
-{
-	return luxincp(disp, -p);
-}
-
-int
-intlen(int n)
-{
-	return    n < 10         ? 1
-		: n < 100        ? 2
-		: n < 1000       ? 3
-		: n < 10000      ? 4
-		: n < 100000     ? 5
-		: n < 1000000    ? 6
-		: n < 10000000   ? 7
-		: n < 100000000  ? 8
-		: n < 1000000000 ? 9
-		: 10;
-}
-
-int
-getdir(void)
-{
-	int fd, dfd;
-	struct dirent *dp;
-	DIR *dir;
-
-	/* To get the file descriptor for the directory where all the brightness
-	 * files are located, we first need to open BACKLIGHT_DIR which is the
-	 * directory where the backlight directories are located.  Then we need
-	 * to get a DIR* of that directory and get the 3rd entry.  We need the
-	 * third because the fist and second are the . and .. folders.  Finally
-	 * we open the folder so that we have a file descriptor we can return.
-	 */
-	if ((dfd = open(BACKLIGHT_DIR, O_RDONLY)) == -1
-			|| (dir = fdopendir(dfd)) == NULL
-			|| (dp  = readdir(dir))   == NULL
-			|| (dp  = readdir(dir))   == NULL
-			|| (dp  = readdir(dir))   == NULL
-			|| (fd  = openat(dfd, dp->d_name, GETDIR_FLAGS)) == -1)
-		return -1;
-
-	closedir(dir);
-	return fd;
-}
-
-FILE *
-getbstream(int dirfd)
-{
-	return fdopen(openat(dirfd, "brightness", O_RDWR), "r+");
-}
diff --git a/src/common.c b/src/common.c
new file mode 100644
index 0000000..6ae23a7
--- /dev/null
+++ b/src/common.c
@@ -0,0 +1,27 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <fcntl.h>
+#include <stdio.h>
+
+#include "common.h"
+
+FILE *
+getbstream(int dirfd)
+{
+	return fdopen(openat(dirfd, "brightness", O_RDWR), "r+");
+}
diff --git a/src/common.h b/src/common.h
new file mode 100644
index 0000000..a7739c2
--- /dev/null
+++ b/src/common.h
@@ -0,0 +1,31 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef LUX_COMMON_H
+#define LUX_COMMON_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+FILE *getbstream(int);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !LUX_COMMON_H */
diff --git a/lux.h b/src/lux.h
index 2ac1637..9296bc5 100644
--- a/lux.h
+++ b/src/lux.h
@@ -20,29 +20,35 @@
 
 #include <stdio.h>
 
-#define BACKLIGHT_DIR "/sys/class/backlight"
+#define LUX_BACKLIGHT_DIR "/sys/class/backlight"
+#ifdef O_PATH
+	#define LUX_GDIR_FLAGS O_PATH
+#else
+	#define LUX_GDIR_FLAGS (O_RDONLY | O_DIRECTORY)
+#endif
+
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-struct luxdisp {
+typedef struct {
 	int __dirfd, __max;
 	FILE *__bstream;
-};
-
-void luxfree(struct luxdisp *);
-int luxinit(struct luxdisp *);
-int luxmax(struct luxdisp *);
-int luxget(struct luxdisp *);
-int luxset(struct luxdisp *, int);
-int luxinc(struct luxdisp *, int);
-int luxdec(struct luxdisp *, int);
-
-double luxgetp(struct luxdisp *);
-double luxsetp(struct luxdisp *, double);
-double luxincp(struct luxdisp *, double);
-double luxdecp(struct luxdisp *, double);
+} lux_t;
+
+void luxfree(lux_t *);
+int luxinit(lux_t *);
+int luxmax(lux_t *);
+int luxget(lux_t *);
+int luxset(lux_t *, int);
+int luxinc(lux_t *, int);
+int luxdec(lux_t *, int);
+
+double luxgetp(lux_t *);
+double luxsetp(lux_t *, double);
+double luxincp(lux_t *, double);
+double luxdecp(lux_t *, double);
 
 #ifdef __cplusplus
 }
diff --git a/src/luxdec.c b/src/luxdec.c
new file mode 100644
index 0000000..2554bfd
--- /dev/null
+++ b/src/luxdec.c
@@ -0,0 +1,24 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "lux.h"
+
+int
+luxdec(lux_t *disp, int n)
+{
+	return luxinc(disp, -n);
+}
diff --git a/src/luxdecp.c b/src/luxdecp.c
new file mode 100644
index 0000000..6bf2c4c
--- /dev/null
+++ b/src/luxdecp.c
@@ -0,0 +1,24 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "lux.h"
+
+double
+luxdecp(lux_t *disp, double p)
+{
+	return luxincp(disp, -p);
+}
diff --git a/src/luxfree.c b/src/luxfree.c
new file mode 100644
index 0000000..579f3b5
--- /dev/null
+++ b/src/luxfree.c
@@ -0,0 +1,30 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+
+#include "lux.h"
+
+void
+luxfree(lux_t *disp)
+{
+	if (disp->__dirfd != -1)
+		close(disp->__dirfd);
+	if (disp->__bstream != NULL)
+		fclose(disp->__bstream);
+}
diff --git a/src/luxget.c b/src/luxget.c
new file mode 100644
index 0000000..39c3b6f
--- /dev/null
+++ b/src/luxget.c
@@ -0,0 +1,39 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdio.h>
+
+#include "common.h"
+#include "lux.h"
+
+int
+luxget(lux_t *disp)
+{
+	/* If we don't have an open stream with the brightness file yet then
+	 * open one.  If we do, we instead rewind to the start of the file so
+	 * that we don't just read an EOF.
+	 */
+	if (disp->__bstream == NULL) {
+		if ((disp->__bstream = getbstream(disp->__dirfd)) == NULL)
+			return -1;
+	} else
+		rewind(disp->__bstream);
+
+	int n;
+	fscanf(disp->__bstream, "%d", &n);
+	return n;
+}
diff --git a/src/luxgetp.c b/src/luxgetp.c
new file mode 100644
index 0000000..8304bb5
--- /dev/null
+++ b/src/luxgetp.c
@@ -0,0 +1,27 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "lux.h"
+
+double
+luxgetp(lux_t *disp)
+{
+	int cur, max;
+	if ((cur = luxget(disp)) == -1 || (max = luxmax(disp)) == -1)
+		return -1;
+	return (double) cur / max * 100;
+}
diff --git a/src/luxinc.c b/src/luxinc.c
new file mode 100644
index 0000000..0849205
--- /dev/null
+++ b/src/luxinc.c
@@ -0,0 +1,24 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "lux.h"
+
+int
+luxinc(lux_t *disp, int n)
+{
+	return luxset(disp, luxget(disp) + n);
+}
diff --git a/src/luxincp.c b/src/luxincp.c
new file mode 100644
index 0000000..d8ff3cb
--- /dev/null
+++ b/src/luxincp.c
@@ -0,0 +1,24 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "lux.h"
+
+double
+luxincp(lux_t *disp, double p)
+{
+	return luxsetp(disp, luxgetp(disp) + p);
+}
diff --git a/src/luxinit.c b/src/luxinit.c
new file mode 100644
index 0000000..ae25925
--- /dev/null
+++ b/src/luxinit.c
@@ -0,0 +1,68 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+
+#include <dirent.h>
+#include <fcntl.h>
+
+#include "lux.h"
+
+static int getdir(void);
+
+int
+luxinit(lux_t *disp)
+{
+	/* Set the default values for the luxdisp struct.  We want to be as lazy
+	 * as possible, so we don't bother with __bstream and __max yet.  We do
+	 * need __dirfd though.
+	 */
+	*disp = (lux_t) {
+		.__bstream = NULL,
+		.__max     = -1,
+		.__dirfd   = getdir()
+	};
+	return disp->__dirfd;
+}
+
+int
+getdir(void)
+{
+	int fd, dfd;
+	struct dirent *dp;
+	DIR *dir;
+
+	/* To get the file descriptor for the directory where all the brightness
+	 * files are located, we first need to open LUX_BACKLIGHT_DIR which is
+	 * the directory where the backlight directories are located.  Then we
+	 * need to get a DIR* of that directory and get the 3rd entry.  We need
+	 * the third because the fist and second are the . and .. folders.
+	 * Finally we open the folder so that we have a file descriptor we can
+	 * return.
+	 */
+	if ((dfd = open(LUX_BACKLIGHT_DIR, O_RDONLY)) == -1
+			|| (dir = fdopendir(dfd)) == NULL)
+		return -1;
+	if ((dp = readdir(dir)) == NULL
+			|| (dp = readdir(dir)) == NULL
+			|| (dp = readdir(dir)) == NULL
+			|| (fd = openat(dfd, dp->d_name, LUX_GDIR_FLAGS)) == -1)
+		fd = -1;
+
+	closedir(dir);
+	return fd;
+}
diff --git a/src/luxmax.c b/src/luxmax.c
new file mode 100644
index 0000000..b30f02b
--- /dev/null
+++ b/src/luxmax.c
@@ -0,0 +1,45 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "lux.h"
+
+int
+luxmax(lux_t *disp)
+{
+	/* The maximum brightness shouldn't change, so we can cache it in the
+	 * struct.
+	 */
+	if (disp->__max != -1)
+		return disp->__max;
+
+	int fd = openat(disp->__dirfd, "max_brightness", O_RDONLY);
+	if (fd == -1)
+		return -1;
+	FILE *stream = fdopen(fd, "r");
+	if (stream == NULL) {
+		close(fd);
+		return -1;
+	}
+
+	fscanf(stream, "%d", &disp->__max);
+	fclose(stream);
+	return disp->__max;
+}
diff --git a/src/luxset.c b/src/luxset.c
new file mode 100644
index 0000000..b707efd
--- /dev/null
+++ b/src/luxset.c
@@ -0,0 +1,58 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "lux.h"
+
+static int intlen(int);
+
+int
+luxset(lux_t *disp, int n)
+{
+	/* The same deal as in luxget() */
+	if (disp->__bstream == NULL) {
+		if ((disp->__bstream = getbstream(disp->__dirfd)) == NULL)
+			return -1;
+	} else
+		rewind(disp->__bstream);
+
+	/* After writing the new brightness value to the brightness file, we
+	 * need to truncate it so that luxset(disp, 1234); luxset(disp, 9);
+	 * gives us a final brightness of 2 and not 9234.
+	 */
+	fprintf(disp->__bstream, "%d", n);
+	ftruncate(fileno(disp->__bstream), intlen(n));
+	return n;
+}
+
+int
+intlen(int n)
+{
+	return    n < 10         ? 1
+		: n < 100        ? 2
+		: n < 1000       ? 3
+		: n < 10000      ? 4
+		: n < 100000     ? 5
+		: n < 1000000    ? 6
+		: n < 10000000   ? 7
+		: n < 100000000  ? 8
+		: n < 1000000000 ? 9
+		: 10;
+}
diff --git a/src/luxsetp.c b/src/luxsetp.c
new file mode 100644
index 0000000..1ec1d61
--- /dev/null
+++ b/src/luxsetp.c
@@ -0,0 +1,25 @@
+/*
+ * BSD Zero Clause License
+ *
+ * Copyright (c) 2022 Thomas Voss
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "lux.h"
+
+double
+luxsetp(lux_t *disp, double p)
+{
+	int max = luxmax(disp);
+	return max == -1 ? -1 : luxset(disp, (int) (p / 100 * max));
+}