Add support for WSL2 Native GUI capability

[Lucy Llewellyn]

I'd like to see Windows Subsystem for Linux 2 (WSL2) support added so that if/when Systemd becomes possible or hacked in via a PID namespace [1] then GUI snaps can be executed without issue. Currently this works fine for non-GUI applications, but WSL has recently enabled native GUI capability via a sidecar distro running a Wayland+Weston server with PulseAudio.

From an examination of how Microsoft are setting up the WSL2 Native GUI capability, the following are important things to note:

WSL sets the environment variables:

DISPLAY=:0
PULSE_SERVER=/mnt/wslg/PulseServer
WAYLAND_DISPLAY=wayland-0
XDG_RUNTIME_DIR=/mnt/wslg/runtime-dir

WSL exposes the following sockets at: /mnt/wslg/runtime-dir/wayland-0

WSL exposes the .X11-unix tree at: /mnt/wslg/.X11-unix This is by default symlinked to /tmp/.X11-unix causing the snap-confine bind mount attempt to fail.

WSL exposes the following PulseAudio sockets:
/mnt/wslg/PulseServer
/mnt/wslg/PulseAudioRDPSink # access may not be needed to this?
/mnt/wslg/PulseAudioRDPSource # access may not be needed to this?
/mnt/wslg/runtime-dir/pulse/native
/mnt/wslg/runtime-dir/pulse/pid # not a socket file but should still be included

In addition, WSL2 starts a dbus daemon which creates the following directory with no files within:

/mnt/wslg/runtime-dir/dbus-1/services/

Also, it appears that a dconf daemon is started with the following runtime file:

/mnt/wslg/runtime-dir/dconf/user

[1]: https://github.com/diddledan/one-script-wsl2-systemd/tree/build-21286+

[Paweł Stołowski (stolowski)]

Daniel, thanks for gathering this information and for investigation, this is interesting! I don't know of any immediate plans for supporting this, but this may change in the future of course.

Also, I noticed you later reported a success with https://forum.snapcraft.io/t/gui-snaps-in-wsl2/23880 ; is there anything to update in this bug report with regard to that story?

[Lucy Llewellyn (lucyllewy)]

I think everything I mentioned is still accurate. The only thing missing now is 3D acceleration via libraries added to `/usr/lib/wsl/lib` via a mount through the hyper-v socket to the host system. These libraries are referenced in a new file created at `/etc/ld.so.conf.d/ld.wsl.conf`.

Neither the libraries, nor the ld.so configuration letting apps know where they are located, are visible to strictly confined snaps, currently.