From 10324228fed7d26d0cae908e1ec84b15548cb8cc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marco=20Trevisan=20=28Trevi=C3=B1o=29?= <mail@3v1n0.net>
Date: Fri, 20 May 2016 04:18:52 +0200
Subject: [PATCH] UpKbdBacklight: don't cache the brightness level, always read
 it from sysfs attrib

When GetBrightness is called it's better to fetch the current value in the
sysfs attribute since many devices doesn't support the emission of brightness
changes to userland, and this could make settings daemons to handle
this value incorrectly.

Add static up_kbd_backlight_brightness_read that is now called during
initialization too, it returns -1 on errors, and use it everywhere we need
to read or check the current brightness.

https://bugs.freedesktop.org/show_bug.cgi?id=95457
---
 src/up-kbd-backlight.c | 69 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 49 insertions(+), 20 deletions(-)

diff --git a/src/up-kbd-backlight.c b/src/up-kbd-backlight.c
index cfa1dd3..b8e45af 100644
--- a/src/up-kbd-backlight.c
+++ b/src/up-kbd-backlight.c
@@ -43,13 +43,43 @@ static void     up_kbd_backlight_finalize   (GObject	*object);
 struct UpKbdBacklightPrivate
 {
 	gint			 fd;
-	gint			 brightness;
 	gint			 max_brightness;
 };
 
 G_DEFINE_TYPE (UpKbdBacklight, up_kbd_backlight, UP_TYPE_EXPORTED_KBD_BACKLIGHT_SKELETON)
 
 /**
+ * up_kbd_backlight_brightness_read:
+ **/
+static gint
+up_kbd_backlight_brightness_read (UpKbdBacklight *kbd_backlight)
+{
+	gchar buf[16];
+	gchar *end = NULL;
+	ssize_t len;
+	gint64 brightness = -1;
+
+	g_return_val_if_fail (kbd_backlight->priv->fd >= 0, brightness);
+
+	lseek (kbd_backlight->priv->fd, 0, SEEK_SET);
+	len = read (kbd_backlight->priv->fd, buf, G_N_ELEMENTS (buf) - 1);
+
+	if (len > 0) {
+		buf[len] = '\0';
+		brightness = g_ascii_strtoll (buf, &end, 10);
+
+		if (brightness < 0 ||
+		    brightness > kbd_backlight->priv->max_brightness ||
+		    end == buf || *end != '\0') {
+			brightness = -1;
+			g_warning ("failed to convert brightness: %s", buf);
+		}
+	}
+
+	return brightness;
+}
+
+/**
  * up_kbd_backlight_brightness_write:
  **/
 static gboolean
@@ -84,9 +114,8 @@ up_kbd_backlight_brightness_write (UpKbdBacklight *kbd_backlight, gint value)
 	}
 
 	/* emit signal */
-	kbd_backlight->priv->brightness = value;
 	up_exported_kbd_backlight_emit_brightness_changed (UP_EXPORTED_KBD_BACKLIGHT (kbd_backlight),
-							   kbd_backlight->priv->brightness);
+        						   value);
 
 out:
 	g_free (text);
@@ -103,8 +132,19 @@ up_kbd_backlight_get_brightness (UpExportedKbdBacklight *skeleton,
 				 GDBusMethodInvocation *invocation,
 				 UpKbdBacklight *kbd_backlight)
 {
-	up_exported_kbd_backlight_complete_get_brightness (skeleton, invocation,
-							   kbd_backlight->priv->brightness);
+	gint brightness;
+
+	brightness = up_kbd_backlight_brightness_read (kbd_backlight);
+
+	if (brightness >= 0) {
+		up_exported_kbd_backlight_complete_get_brightness (skeleton, invocation,
+								   brightness);
+	} else {
+		g_dbus_method_invocation_return_error (invocation,
+						       UP_DAEMON_ERROR, UP_DAEMON_ERROR_GENERAL,
+						       "error reading brightness");
+	}
+
 	return TRUE;
 }
 
@@ -216,23 +256,12 @@ up_kbd_backlight_find (UpKbdBacklight *kbd_backlight)
 		goto out;
 	}
 
-	/* read brightness */
+	/* open the brightness file for read and write operations */
 	path_now = g_build_filename (dir_path, "brightness", NULL);
-	ret = g_file_get_contents (path_now, &buf_now, NULL, &error);
-	if (!ret) {
-		g_warning ("failed to get brightness: %s", error->message);
-		g_error_free (error);
-		goto out;
-	}
-	kbd_backlight->priv->brightness = g_ascii_strtoull (buf_now, &end, 10);
-	if (kbd_backlight->priv->brightness == 0 && end == buf_now) {
-		g_warning ("failed to convert brightness: %s", buf_now);
-		goto out;
-	}
-
-	/* open the file for writing */
 	kbd_backlight->priv->fd = open (path_now, O_RDWR);
-	if (kbd_backlight->priv->fd < 0)
+
+	/* read brightness and check if it has an acceptable value */
+	if (up_kbd_backlight_brightness_read (kbd_backlight) < 0)
 		goto out;
 
 	/* success */
-- 
1.9.1