backlight: do nothing if max_brightness is 0

[elogind.git] / src / backlight / backlight.c

diff --git a/src/backlight/backlight.c b/src/backlight/backlight.c
index 86f10cc0cf290f15dc5978a74e8a3b9d9f04add3..ce0385b08c4df67c5b533f8205b787189012937d 100644 (file)
--- a/src/backlight/backlight.c
+++ b/src/backlight/backlight.c
@@ -192,11 +192,61 @@ static bool validate_device(struct udev *udev, struct udev_device *device) {
         return true;
 }
 
+static unsigned get_max_brightness(struct udev_device *device) {
+        int r;
+        const char *max_brightness_str;
+        unsigned max_brightness;
+
+        max_brightness_str = udev_device_get_sysattr_value(device, "max_brightness");
+        if (!max_brightness_str) {
+                log_warning("Failed to read max_brightness attribute");
+                return 0;
+        }
+
+        r = safe_atou(max_brightness_str, &max_brightness);
+        if (r < 0) {
+                log_warning("Failed to parse max_brightness \"%s\": %s", max_brightness_str, strerror(-r));
+                return 0;
+        }
+
+        return max_brightness;
+}
+
+/* Some systems turn the backlight all the way off at the lowest levels.
+ * clamp_brightness clamps the saved brightness to at least 1 or 5% of
+ * max_brightness.  This avoids preserving an unreadably dim screen, which
+ * would otherwise force the user to disable state restoration. */
+static void clamp_brightness(struct udev_device *device, char **value, unsigned max_brightness) {
+        int r;
+        unsigned brightness, new_brightness;
+
+        r = safe_atou(*value, &brightness);
+        if (r < 0) {
+                log_warning("Failed to parse brightness \"%s\": %s", *value, strerror(-r));
+                return;
+        }
+
+        new_brightness = MAX3(brightness, 1U, max_brightness/20);
+        if (new_brightness != brightness) {
+                char *old_value = *value;
+
+                r = asprintf(value, "%u", new_brightness);
+                if (r < 0) {
+                        log_oom();
+                        return;
+                }
+
+                log_debug("Saved brightness %s too low; increasing to %s.", old_value, *value);
+                free(old_value);
+        }
+}
+
 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, *escaped_ss = NULL, *escaped_sysname = NULL, *escaped_path_id = NULL;
         const char *sysname, *path_id;
+        unsigned max_brightness;
         int r;
 
         if (argc != 3) {
@@ -252,6 +302,14 @@ int main(int argc, char *argv[]) {
                 return EXIT_FAILURE;
         }
 
+        /* If max_brightness is 0, then there is no actual backlight
+         * device. This happens on desktops with Asus mainboards
+         * that load the eeepc-wmi module.
+         */
+        max_brightness = get_max_brightness(device);
+        if (max_brightness == 0)
+                return EXIT_SUCCESS;
+
         escaped_ss = cescape(ss);
         if (!escaped_ss) {
                 log_oom();
@@ -306,6 +364,8 @@ int main(int argc, char *argv[]) {
                         return EXIT_FAILURE;
                 }
 
+                clamp_brightness(device, &value, max_brightness);
+
                 r = udev_device_set_sysattr_value(device, "brightness", value);
                 if (r < 0) {
                         log_error("Failed to write system attribute: %s", strerror(-r));
@@ -322,7 +382,7 @@ int main(int argc, char *argv[]) {
 
                 value = udev_device_get_sysattr_value(device, "brightness");
                 if (!value) {
-                        log_error("Failed to read system attribute: %s", strerror(-r));
+                        log_error("Failed to read system attribute");
                         return EXIT_FAILURE;
                 }