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
