backlight: add minimal tool to save/restore screen brightness across reboots

As many laptops don't save/restore screen brightness across reboots,
let's do this in systemd with a minimal tool, that restores the
brightness as early as possible, and saves it as late as possible. This
will cover consoles and graphical logins, but graphical desktops should
do their own per-user stuff probably.

This only touches firmware brightness controls for now.

2 files changed, 127 insertions, 0 deletions

diff --git a/src/backlight/Makefile b/src/backlight/Makefile
new file mode 120000
index 0000000000..d0b0e8e008
--- /dev/null
+++ b/src/backlight/Makefile
@@ -0,0 +1 @@
+../Makefile
\ No newline at end of file
diff --git a/src/backlight/backlight.c b/src/backlight/backlight.c
new file mode 100644
index 0000000000..3378907f91
--- /dev/null
+++ b/src/backlight/backlight.c
@@ -0,0 +1,126 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <libudev.h>
+
+#include "util.h"
+#include "mkdir.h"
+#include "fileio.h"
+
+int main(int argc, char *argv[]) {
+        struct udev *udev = NULL;
+        struct udev_device *device = NULL;
+        _cleanup_free_ char *saved = NULL;
+        int r;
+
+        if (argc != 3) {
+                log_error("This program requires two arguments.");
+                return EXIT_FAILURE;
+        }
+
+        log_set_target(LOG_TARGET_AUTO);
+        log_parse_environment();
+        log_open();
+
+        umask(0022);
+
+        r = mkdir_p("/var/lib/backlight", 0755);
+        if (r < 0) {
+                log_error("Failed to create backlight directory: %s", strerror(-r));
+                goto finish;
+        }
+
+        udev = udev_new();
+        if (!udev) {
+                r = log_oom();
+                goto finish;
+        }
+
+        device = udev_device_new_from_syspath(udev, argv[2]);
+        if (!device) {
+                r = log_oom();
+                goto finish;
+        }
+
+        if (!streq_ptr(udev_device_get_subsystem(device), "backlight")) {
+                log_error("Not a backlight device: %s", argv[2]);
+                r = -ENODEV;
+                goto finish;
+        }
+
+        saved = strappend("/var/lib/backlight/", udev_device_get_sysname(device));
+        if (!saved) {
+                r = log_oom();
+                goto finish;
+        }
+
+        if (streq(argv[1], "load")) {
+                _cleanup_free_ char *value = NULL;
+
+                r = read_one_line_file(saved, &value);
+                if (r < 0) {
+
+                        if (r == -ENOENT) {
+                                r = 0;
+                                goto finish;
+                        }
+
+                        log_error("Failed to read %s: %s", saved, strerror(-r));
+                        goto finish;
+                }
+
+                r = udev_device_set_sysattr_value(device, "brightness", value);
+                if (r < 0) {
+                        log_error("Failed to write system attribute: %s", strerror(-r));
+                        goto finish;
+                }
+
+        } else if (streq(argv[1], "save")) {
+                const char *value;
+
+                value = udev_device_get_sysattr_value(device, "brightness");
+                if (!value) {
+                        log_error("Failed to read system attribute: %s", strerror(-r));
+                        goto finish;
+                }
+
+                r = write_string_file(saved, value);
+                if (r < 0) {
+                        log_error("Failed to write %s: %s", saved, strerror(-r));
+                        goto finish;
+                }
+
+        } else {
+                log_error("Unknown verb %s.", argv[1]);
+                r = -EINVAL;
+                goto finish;
+        }
+
+finish:
+        if (device)
+                udev_device_unref(device);
+
+        if (udev)
+                udev_unref(udev);
+
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+
+}