path: root/src/backlight/backlight.c

/*-*- 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 "util.h"
#include "mkdir.h"
#include "fileio.h"
#include "libudev.h"
#include "udev-util.h"

static struct udev_device *find_pci_or_platform_parent(struct udev_device *device) {
        struct udev_device *parent;
        const char *subsystem, *sysname;

        assert(device);

        parent = udev_device_get_parent(device);
        if (!parent)
                return NULL;

        subsystem = udev_device_get_subsystem(parent);
        if (!subsystem)
                return NULL;

        sysname = udev_device_get_sysname(parent);
        if (!sysname)
                return NULL;

        if (streq(subsystem, "drm")) {
                const char *c;

                c = startswith(sysname, "card");
                if (!c)
                        return NULL;

                c += strspn(c, "0123456789");
                if (*c == '-') {
                        /* A connector DRM device, let's ignore all but LVDS and eDP! */

                        if (!startswith(c, "-LVDS-") &&
                            !startswith(c, "-Embedded DisplayPort-"))
                                return NULL;
                }

        } else if (streq(subsystem, "pci")) {
                const char *value;

                value = udev_device_get_sysattr_value(parent, "class");
                if (value) {
                        unsigned long class;

                        if (safe_atolu(value, &class) < 0) {
                                log_warning("Cannot parse PCI class %s of device %s:%s.", value, subsystem, sysname);
                                return NULL;
                        }

                        /* Graphics card */
                        if (class == 0x30000)
                                return parent;
                }

        } else if (streq(subsystem, "platform"))
                return parent;

        return find_pci_or_platform_parent(parent);
}

static bool same_device(struct udev_device *a, struct udev_device *b) {
        assert(a);
        assert(b);

        if (!streq_ptr(udev_device_get_subsystem(a), udev_device_get_subsystem(b)))
                return false;

        if (!streq_ptr(udev_device_get_sysname(a), udev_device_get_sysname(b)))
                return false;

        return true;
}

static bool validate_device(struct udev *udev, struct udev_device *device) {
        _cleanup_udev_enumerate_unref_ struct udev_enumerate *enumerate = NULL;
        struct udev_list_entry *item = NULL, *first = NULL;
        struct udev_device *parent;
        const char *v, *subsystem;
        int r;

        assert(udev);
        assert(device);

        /* Verify whether we should actually care for a specific
         * backlight device. For backlight devices there might be
         * multiple ways to access the same control: "firmware"
         * (i.e. ACPI), "platform" (i.e. via the machine's EC) and
         * "raw" (via the graphics card). In general we should prefer
         * "firmware" (i.e. ACPI) or "platform" access over "raw"
         * access, in order not to confuse the BIOS/EC, and
         * compatibility with possible low-level hotkey handling of
         * screen brightness. The kernel will already make sure to
         * expose only one of "firmware" and "platform" for the same
         * device to userspace. However, we still need to make sure
         * that we use "raw" only if no "firmware" or "platform"
         * device for the same device exists. */

        subsystem = udev_device_get_subsystem(device);
        if (!streq_ptr(subsystem, "backlight"))
                return true;

        v = udev_device_get_sysattr_value(device, "type");
        if (!streq_ptr(v, "raw"))
                return true;

        parent = find_pci_or_platform_parent(device);
        if (!parent)
                return true;

        subsystem = udev_device_get_subsystem(parent);
        if (!subsystem)
                return true;

        enumerate = udev_enumerate_new(udev);
        if (!enumerate)
                return true;

        r = udev_enumerate_add_match_subsystem(enumerate, "backlight");
        if (r < 0)
                return true;

        r = udev_enumerate_scan_devices(enumerate);
        if (r < 0)
                return true;

        first = udev_enumerate_get_list_entry(enumerate);
        udev_list_entry_foreach(item, first) {
                _cleanup_udev_device_unref_ struct udev_device *other;
                struct udev_device *other_parent;
                const char *other_subsystem;

                other = udev_device_new_from_syspath(udev, udev_list_entry_get_name(item));
                if (!other)
                        return true;

                if (same_device(device, other))
                        continue;

                v = udev_device_get_sysattr_value(other, "type");
                if (!streq_ptr(v, "platform") && !streq_ptr(v, "firmware"))
                        continue;

                /* OK, so there's another backlight device, and it's a
                 * platform or firmware device, so, let's see if we
                 * can verify it belongs to the same device as
                 * ours. */
                other_parent = find_pci_or_platform_parent(other);
                if (!other_parent)
                        continue;

                if (same_device(parent, other_parent)) {
                        /* Both have the same PCI parent, that means
                         * we are out. */
                        log_debug("Skipping backlight device %s, since backlight device %s is on same PCI device and, takes precedence.", udev_device_get_sysname(device), udev_device_get_sysname(other));
                        return false;
                }

                other_subsystem = udev_device_get_subsystem(other_parent);
                if (streq_ptr(other_subsystem, "platform") && streq_ptr(subsystem, "pci")) {
                        /* The other is connected to the platform bus
                         * and we are a PCI device, that also means we
                         * are out. */
                        log_debug("Skipping backlight device %s, since backlight device %s is a platform device and takes precedence.", udev_device_get_sysname(device), udev_device_get_sysname(other));
                        return false;
                }
        }

        return true;
}

int main(int argc, char *argv[]) {
        _cleanup_udev_unref_ struct udev *udev = NULL;
        _cleanup_udev_device_unref_ struct udev_device *device = NULL;
        _cleanup_free_ char *saved = NULL, *ss = NULL;
        const char *sysname;
        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/systemd/backlight", 0755);
        if (r < 0) {
                log_error("Failed to create backlight directory: %s", strerror(-r));
                return EXIT_FAILURE;
        }

        udev = udev_new();
        if (!udev) {
                log_oom();
                return EXIT_FAILURE;
        }

        sysname = strchr(argv[2], ':');
        if (!sysname) {
                log_error("Requires pair of subsystem and sysname for specifying backlight device.");
                return EXIT_FAILURE;
        }

        ss = strndup(argv[2], sysname - argv[2]);
        if (!ss) {
                log_oom();
                return EXIT_FAILURE;
        }

        sysname++;

        if (!streq(ss, "backlight") && !streq(ss, "leds")) {
                log_error("Not a backlight or LED device: '%s:%s'", ss, sysname);
                return EXIT_FAILURE;
        }

        errno = 0;
        device = udev_device_new_from_subsystem_sysname(udev, ss, sysname);
        if (!device) {
                if (errno != 0)
                        log_error("Failed to get backlight or LED device '%s:%s': %m", ss, sysname);
                else
                        log_oom();

                return EXIT_FAILURE;
        }

        saved = strjoin("/var/lib/systemd/backlight/", ss, ":", sysname, NULL);
        if (!saved) {
                log_oom();
                return EXIT_FAILURE;
        }

        /* If there are multiple conflicting backlight devices, then
         * their probing at boot-time might happen in any order. This
         * means the validity checking of the device then is not
         * reliable, since it might not see other devices conflicting
         * with a specific backlight. To deal with this we will
         * actively delete backlight state files at shutdown (where
         * device probing should be complete), so that the validity
         * check at boot time doesn't have to be reliable. */

        if (streq(argv[1], "load")) {
                _cleanup_free_ char *value = NULL;

                if (!validate_device(udev, device))
                        return EXIT_SUCCESS;

                r = read_one_line_file(saved, &value);
                if (r < 0) {

                        if (r == -ENOENT)
                                return EXIT_SUCCESS;

                        log_error("Failed to read %s: %s", saved, strerror(-r));
                        return EXIT_FAILURE;
                }

                r = udev_device_set_sysattr_value(device, "brightness", value);
                if (r < 0) {
                        log_error("Failed to write system attribute: %s", strerror(-r));
                        return EXIT_FAILURE;
                }

        } else if (streq(argv[1], "save")) {
                const char *value;

                if (!validate_device(udev, device)) {
                        unlink(saved);
                        return EXIT_SUCCESS;
                }

                value = udev_device_get_sysattr_value(device, "brightness");
                if (!value) {
                        log_error("Failed to read system attribute: %s", strerror(-r));
                        return EXIT_FAILURE;
                }

                r = write_string_file(saved, value);
                if (r < 0) {
                        log_error("Failed to write %s: %s", saved, strerror(-r));
                        return EXIT_FAILURE;
                }

        } else {
                log_error("Unknown verb %s.", argv[1]);
                return EXIT_FAILURE;
        }

        return EXIT_SUCCESS;
}