Created attachment 325697 [details]
Patch for current gdm-2.16 package in EL5

Description of problem:

The gdmgreeter will fail to start if a xinput device is defined in the xorg.conf but is not actually plugged in.

This happens for example when a Wacom tablet was added in xorg.conf but the device is not plugged in when gdm starts.


Version-Release number of selected component (if applicable):

    gdm-2.16.0-46

How reproducible:

    100% reproducible

Steps to Reproduce:
1. Add devices to teh xorg.conf

        InputDevice    "stylus" "SendCoreEvents"
        InputDevice    "eraser" "SendCoreEvents"
        InputDevice    "cursor" "SendCoreEvents"

        Section "InputDevice"
                Identifier  "stylus"
                Driver      "wacom"
        ...
        EndSection
        
        Section "InputDevice"
                Identifier  "eraser"
                Driver      "wacom"
        ...
        EndSection
        
        Section "InputDevice"
                Identifier  "cursor"
                Driver      "wacom"
        ...
        EndSection

2. Do _not_ plug any additional device
3. Restart gdm
  
Actual results:

    “The greeter application appears to be crashing.
     Attempting to use a different one.”

Expected results:

The greeter is displayed correctly.

Additional info:

The problem comes from the additional modules dwellmouselistener and keymouselistener which try to open the extended devices reported by XInput without checking for errors.

In gui/modules/keymouselistener.c and gui/modules/dwellmouselistener.c, the same code is duplicated and does:


   static void
   init_xinput (GdkDisplay *display, GdkWindow *root)
   {
   ...
       devices = XListInputDevices (GDK_DISPLAY_XDISPLAY (display),
           &num_devices);

   ...

       for (i=0; i < num_devices; i++) {
           if (devices[i].use == IsXExtensionDevice) {
               device = XOpenDevice (GDK_DISPLAY_XDISPLAY (display),
                   devices[i].id);
               for (j=0; j < device->num_classes && number < 39; j++) {
                   switch (device->classes[j].input_class)
                   {

   ...

That code works in most cases, except when the device is defined but not actually there, in which case the call to XOpenDevice() will cause an X error. Since there is no mechanism in place to trap that error, the gdmgreeter will fail and cause the error reported.

The proper way (IMHO) to handle this is to protect the call to XOpenDevice() by wrapping it in an X error handler, ie change the code to:

   static void
   init_xinput (GdkDisplay *display, GdkWindow *root)
   {
   ...
       devices = XListInputDevices (GDK_DISPLAY_XDISPLAY (display),
           &num_devices);

   ...

       for (i=0; i < num_devices; i++) {
           if (devices[i].use == IsXExtensionDevice) {
               gdk_error_trap_push ();
               device = XOpenDevice (GDK_DISPLAY_XDISPLAY (display),
                   devices[i].id);
               if (gdk_error_trap_pop())
               {
                   if (debug_gestures)
                       syslog (LOG_WARNING, "Failed to open input devices %i (%s)",
                           devices[i].id, devices[i].name);
                   continue;
               }
               for (j=0; j < device->num_classes && number < 39; j++) {
                   switch (device->classes[j].input_class)
                   {
   ...


The bug is still upstream (at least in gdm that comes with gnome-2.20, the last one before gdm was changed).