[libvirt] guests and pulseaudio fighting over audio devices

Daniel P. Berrange berrange at redhat.com
Wed Sep 16 09:32:44 UTC 2009

On Tue, Sep 15, 2009 at 04:45:31PM -0400, Dave Allan wrote:
> I noticed that when a KVM guest created with virt-manager is running on 
> F10, sound on the physical host stops working.  When all VMs are 
> shutdown, sound starts working again.  Removing the <sound> tag from the 
> VM XML allows sound to work while the VM is booted.  To further 
> complicate troubleshooting, if audio is already playing when the guest 
> is started it keeps playing, since pulse already has the device open.
> The message in /var/log/messages when I try to play audio is:
> pulseaudio[6492]: module-alsa-sink.c: Error opening PCM device front:0: 
> Device or resource busy
> strace of pulseaudio shows:
> open("/dev/snd/pcmC0D0p", O_RDWR|O_NONBLOCK) = -1 EBUSY (Device or 
> resource busy)
> but fuser and lsof show nothing.  A trivial test program also sees 
> Device or resource busy when trying to open /dev/snd/pcmC0D0p
> I am in favor of removing the <sound> tag from the default 
> configuration, since I don't use sound from within guests and I do use 
> sound on my desktop, but perhaps this behavior is specific to my 
> configuration.  I haven't investigated it exhaustively.  What does 
> everybody else think?

It is complicated :-)  In Fedora >= 11 we currently disable all use of
sound cards, but this upsets people who want sound ;-P  I'm working
on a new version of the patch which sets up audio-over-VNC, while for
SDL allows the host audio backend to be used & configured.

I still need to finish my GTK-VNC patches to do the client end of 
audio over VNC, then it'll all play correctly with desktop audio
services via gstreamer/pulseaudio

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