a77d95af61
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
X Server
The X server accepts requests from client applications to create windows, which are (normally rectangular) "virtual screens" that the client program can draw into.
Windows are then composed on the actual screen by the X server (or by a separate composite manager) as directed by the window manager, which usually communicates with the user via graphical controls such as buttons and draggable titlebars and borders.
For a comprehensive overview of X Server and X Window System, consult the following article: https://en.wikipedia.org/wiki/X_server
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