+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;
+ }
+
+ if (max_brightness <= 0) {
+ log_warning("Maximum brightness is 0, ignoring device.");
+ 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);
+ }
+}
+