[libvirt] guests and pulseaudio fighting over audio devices

[Dave Allan]

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?

Dave