Move pulseaudio to sys-usb

[tfm...@googlemail.com]

I want to use an external USB sound card. With all USB devices in
dom0 this wasn't an issue, but now I have sys-usb and USB forwarding
seems to not agree with my audio device.

I guess it should be possible to move the pulseaudio server from
dom0 to sys-usb, shouldn't it?

Or even better: Have another pulseaudio server in sys-usb and have
an additional sink in dom0 that connects to the server in sys-usb.

Looking at module-vchan-sink.c[1]:

/* FIXME: 0 is remote domain ID */
u->play_ctrl = libvchan_server_init(0, QUBES_PA_SINK_VCHAN_PORT, 128, 2048);

Does this mean that the vchan sink is currently hard-wired to send
to dom0?

[1] https://github.com/QubesOS/qubes-gui-agent-linux/blobk/4427218dc382c66a98e22d5e67bdef5a87a5b3ba/pulse/module-vchan-sink.c#L431-L432

[tfm...@googlemail.com]

> I guess it should be possible to move the pulseaudio server from
> dom0 to sys-usb, shouldn't it?

Found a thread on qubes-devel regarding this [1] and also an open
ticket [2].

[1] https://groups.google.com/forum/#!topic/qubes-devel/kmAjYCP8K_4/discussion
[2] https://github.com/QubesOS/qubes-issues/issues/1590