[pulseaudio-tickets] [Bug 43503] Xen paravirtualized driver frontend module

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=43503

--- Comment #9 from Giorgos Boutsioukis <gboutsioukis at gmail.com> 2012-02-26 16:05:01 PST ---
I made a few cosmetic changes to the patch. xen_gnt.h was a header that
included gntalloc.h and gntdev.h, which are the gnt devices interface headers
from the linux kernel. I have copied both into the modules/xen directory so
that the actual kernel headers don't have to be a dependency and the interface
macros defined shouldn't change in the future. Of course, we can always remove
them and just check for the presence of the actual kernel headers.

As far as detection goes: from your comments and from what I've figured so far,
I think the best solution is to first check if we are in a domU guest in
module-udev-detect. This can be done by checking the presence and contents of
/proc/xen/capabilities; if it doesn't contain 'control_d' then we are in a
guest domain.

Now, if we are in a Xen guest then we know that xenstore will be present. A
simple module (module-xenguest-detect) linked to xenstore can be loaded, look
for an audio backend there and if found, it will finally try to load
module-xenpv-sink. The other option is to keep the detection code in the sink
module and prevent it from loading, but I think it's safer to use a different
module just to make sure that we'll be leaving Xen guests without PV audio
support alone.

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