This commit implements device type discovery by calling two ioctls
(DRM_IOCTL_VERSION and EVIOCGVERSION) on the device. These iocts are
specific to drm and input devices respectively, therefore we can
determine the device type based on which one returns an error.
The VT the compositor was started from was not activated after exiting
the compositor, which resulted in arriving on a blank VT. This commit
fixes that by introducing a new field in direct_session struct that
stores the last active VT so that it can be activated in
direct_session_destroy.
The major device number does not indicate the device type on FreeBSD,
and AFAIK the only way to differentiate between DRM, input, and other
devices is checking the fd path. This commit implements that.
The drmDropmaster and drmSetmaster calls are necessary, because the
implicit drop (that should occur when the DRM fd is closed) seems not
to be working in some scenarios (e.g. if you have a tmux session
running - maybe the fd is retained somehow by tmux?). This is a
problem, because once you exit the compositor, you can't start it (or
any other program that wants to be DRM master) again until you close
all your tmux sessions.
On some systems (most notably laptops with two GPUs) there are GPUs that
don't have attached outputs. However, we still want to load those GPUs
because they could still be used by the compositor for rendering.
recvmsg(3) returns 0 if the connection partner has shut down its socket.
The communicate function considered 0 a successful message, though, and
keeps calling recvmsg(3) again and again.
Xwayland uses SIGUSR1 to signal readiness.
With direct(-freebsd) session and Xwayland, wlroots was confusing the
Xwayland readiness signal with a vt switch signal, freezing the desktop.
Same problem was found in Weston in 2014:
https://phabricator.freedesktop.org/T7080
