uxa: Check for access to backlight interface

Before attaching properties to any connector, check that we can indeed
control the backlight through the sysfs interface by doing an access
check. If the xserver is started without root privileges, we cannot
write through /sys/class/backlight and so should take care not to
advertise that we can.

Reported-by: Hans de Geode <hdegeode@redhat.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

diff --git a/src/uxa/intel_display.c b/src/uxa/intel_display.c
index a4e04ec..e1b2920 100644 (file)
--- a/src/uxa/intel_display.c
+++ b/src/uxa/intel_display.c
@@ -298,6 +298,14 @@ intel_output_backlight_get_max(xf86OutputPtr output)
        char path[BACKLIGHT_PATH_LEN], val[BACKLIGHT_VALUE_LEN];
        int fd, max = 0;
 
+       /* We are used as an initial check to see if we can
+        * control the backlight, so first test if we can set values.
+        */
+       sprintf(path, "%s/%s/brightness",
+               BACKLIGHT_CLASS, intel_output->backlight_iface);
+       if (access(path, R_OK | W_OK))
+               return -1;
+
        sprintf(path, "%s/%s/max_brightness",
                BACKLIGHT_CLASS, intel_output->backlight_iface);
        fd = open(path, O_RDONLY);