xwayland: Check X11 clients prior to terminate Xwayland

Currently, mutter checks for the presence of X11 windows to decide
whether or not Xwayland can be terminated, when Xwayland is started on
demand.

Unfortunately, not all X11 clients will map a window all the time, an
X11 client may keep the X11 connection opened after closing all its
windows. In that case, we may terminate Xwayland while there are some
X11 client connected still, and terminating Xwayland will also kill
those X11 clients.

To avoid that issue, check the X11 clients actually connected using the
XRes extension. The XRes extension provides the PID of the (local) X11
clients connected to the Xserver, so we need to match that against the
actual executable names, and compare with a list of known executables
that we can safely ignore, such as ibus-x11 or gsd-xsettings.

We also check against our own executable name, considering that the X11
window manager is also an X11 client connected to the Xserver.

Also, XRes returning the PID of local clients only is not a problem
considering that Xwayland does not listen to remote connections.
However, if the user spawns a client remotely on another system using
ssh tunneling (ssh -X), only clients which actually map a window will
be accounted for.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1537
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1671>

1 files changed, 3 insertions, 0 deletions

diff --git a/config.h.meson b/config.h.meson
index f4d6000e1..4b7a4a107 100644
--- a/config.h.meson
+++ b/config.h.meson
@@ -82,3 +82,6 @@
 
 /* Whether the memfd_create function exists */
 #mesondefine HAVE_MEMFD_CREATE
+
+/* List of executable names to ignore when terminating Xwayland */
+#mesondefine XWAYLAND_IGNORE_EXECUTABLES