Because of the design of most Wayland compositors, where the compositor
is both a Wayland server and an X11 window manager, any X11 client
issuing a server grab (i.e. XGrabServer()) can possibly hang the whole
desktop when Xwayland is running rootless.
This can happen with e.g. ImageMagick's import command with mutter.
1. "import" is launched and issues an XServerGrab(),
2. Xwayland restricts access to that "import" X11 client alone,
3. mutter continues to process events until it needs to sync with
Xwayland (there's variability in time before the hang occurs),
4. When mutter does an XSync() (explicitly or implicitly through some
other Xlib call), it will stop waiting for Xwayland to reply,
5. Xwayland waits for the XServerGrab() to be released by import,
6. "import" waits for a user input to release the XServerGrab(),
7. mutter is stuck waiting on Xwayland and does not process input
events...
To prevent this, re-route the GrabServer/UngrabServer requests and
pretend the grab works but actually does nothing at all for all clients
but the X11 window manager (which can still issue X11 server grabs, at
its own risks).
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Closes: https://bugzilla.redhat.com/1914021
a77d95af61