Xen users - Mar 2007 - Xen kernel prevents ALSA working

I''m using Xen under Debian Etch.  I''ve managed to get my
virtual
machines working and I''m happy with that.  But I find that if I boot 
Debian using the Xen kernel (version 2.6.18-4-xen-686), ALSA suddenly 
can''t find either of my soundcards (an AC97 on the motherboard and an 
M-Audio M44 PCI card).  Everything else seems to work fine, networking 
and bluetooth and so on.  If I revert to the stock 2.6.18 kernel, ALSA 
has no problems.

One thing that I thought could be the problem is the fact that I''m
using
a 686 kernel, when I''m running on an Athlon processor and really should
be using k7.  Unfortunately Debian doesn''t seem to have any Xen kernels
for k7 at the moment.  But I also tried using the normal 686 kernel, and 
ALSA works fine under that too, so it seems like it shouldn''t be a 
problem with the wrong architecture.

I''ve tried shutting down the xend server, but that doesn''t
help.

I notice that all the correct kernel modules for my soundcards are 
loaded.  ALSA just doesn''t see them, somehow.  It might be that Xen has
reserved the soundcards for its own use, on the grounds that it might 
need them to provide virtual hardware to its guest OSs.  But googling 
around, it seems Xen doesn''t even attempt to provide that kind of 
virtualisation as yet.

Anyone have some hints for me?

Thanks,
Mat

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On Tue, 2007-03-20 at 18:09 +0100, xen.mexon@spamgourmet.com
wrote:
> I''m using Xen under Debian Etch.  I''ve managed to get my
virtual
> machines working and I''m happy with that.  But I find that if I
boot
> Debian using the Xen kernel (version 2.6.18-4-xen-686), ALSA suddenly 
> can''t find either of my soundcards (an AC97 on the motherboard and
an
> M-Audio M44 PCI card).  Everything else seems to work fine, networking 
> and bluetooth and so on.  If I revert to the stock 2.6.18 kernel, ALSA 
> has no problems.
> 
> One thing that I thought could be the problem is the fact that I''m
using
> a 686 kernel, when I''m running on an Athlon processor and really
should
> be using k7.  Unfortunately Debian doesn''t seem to have any Xen
kernels
> for k7 at the moment.  But I also tried using the normal 686 kernel, and 
> ALSA works fine under that too, so it seems like it shouldn''t be a
> problem with the wrong architecture.
> 
> I''ve tried shutting down the xend server, but that
doesn''t help.
> 
> I notice that all the correct kernel modules for my soundcards are 
> loaded.  ALSA just doesn''t see them, somehow.  It might be that
Xen has
> reserved the soundcards for its own use, on the grounds that it might 
> need them to provide virtual hardware to its guest OSs.  But googling 
> around, it seems Xen doesn''t even attempt to provide that kind of 
> virtualisation as yet.
> 
> Anyone have some hints for me?
> 
> Thanks,
> Mat
> 
> ___
Really dumb question, but does lsmod give an indication that the modules
for the sound card have been loaded? Are they in /etc/modules?

There''s several degrees of broken :

1 - lspci won''t see them even with modules loaded, just ''not
working''.

2 - lspci sees them, but they still don''t seem to work with modules
    loaded

3 - the modules themselves fail to load

4 - (and likely) the modules just aren''t loaded on boot

Which one are you experiencing? I''ve never had a problem getting sound
to work (on dom-0 anyway) under Xen since 3.0 was released on
Debian(ish) distros, but I also build from source. 

I moved over to Ubuntu in Lieu of working with Etch, so I''m not really
familiar with how Debian is packaging Xen now but I believe your old
initrd was handling this for you where your new one is not. Seems to be
the common denominator. 

ALSA should also be screaming about something being wrong during boot,
did you happen to catch any messages from / out of dmesg?

Best,
--Tim



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Tim Post - tim.post@netkinetics.net wrote:
> Really dumb question, but does lsmod give an indication that the modules
> for the sound card have been loaded? Are they in /etc/modules?
> 
> There''s several degrees of broken :
> 
> 1 - lspci won''t see them even with modules loaded, just
''not working''.
> 
> 2 - lspci sees them, but they still don''t seem to work with
modules
>     loaded
> 
> 3 - the modules themselves fail to load
> 
> 4 - (and likely) the modules just aren''t loaded on boot
> 
> Which one are you experiencing?
None of the above.  All the correct kernel modules for both my
soundcards are being loaded, without complaints, at least in the syslog.
 The problem is that having loaded all the correct modules, ALSA refuses
to admit that there''s any hardware there.

That is, when ALSA comes up during boot, it tells me "no devices
found"
or something similar (sorry I don''t have the exact message,
I''m away
from that computer right now.)  But when I lsmod, all the correct
devices are loaded, and I don''t know who''s loading those if it
isn''t
ALSA (I can''t remember precisely what''s in my /etc/modules,
but it
definitely doesn''t include the AC97, at least.)

I''ve already run into problems with Xen attempting to grab the network
hardware when it starts, despite the fact that the network hardware is
already up and running.  This results in a big mess and no network
connection for anything.  I fixed that by disabling eth0 from
automatically coming up at boot.  This situation seems very similar, so
a plausible explanation is that Xen is also trying to grab the audio
hardware, despite the fact that ALSA''s already using it, resulting in a
similar big mess and lack of hardware for all concerned.  But this seems
unlikely when you realise that Xen doesn''t provide audio hardware
virtualisation.

I realise now that rather than simply running "/etc/init.d/xend stop",
to fix the mess I really need to disable xend completely and boot again,
and see what happens then.  Unfortunately I''m away from the computer
right now and can''t do that, but I''ll give it a go tonight to
see if
audio works again.  But of course that''s not actually a solution,
it''s
just a bit of diagnosis.

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