Description of problem:
set vnc_allow_host_audio = 1 in /etc/libvirt/qemu.conf , and set QEMU_AUDIO_DRV=vnc in /etc/sysconfig/libvirtd .  Set the guest graphic framebuffer to vnc . Start the guest , look into the guest.log , will find QEMU_AUDIO_DRV be set to none every time. 

Version-Release number of selected component (if applicable):
libvirt-0.8.7-7.el6.x86_64

How reproducible:
always

Steps to Reproduce:
1.set vnc_allow_host_audio = 1 in /etc/libvirt/qemu.conf 
2.set QEMU_AUDIO_DRV=vnc
3.define a guest with following section 
 <graphics type='vnc' port='5900' autoport='yes'/>
4.look into guest.log 
  

  
Actual results:
2011-02-15 19:21:26.737: starting up
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none /usr/libexec/qemu-kvm -S -M rhel6.1.0 -enable-kvm -m 512 -smp 1,sockets=1,cores=1,threads=1 -name netboot -uuid 23a1d939-8034-e58d-f003-cea63d884b6a -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/netboot.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-reboot -boot n -drive file=/var/lib/libvirt/images/netboot.img,if=none,id=drive-ide0-0-0,format=raw,cache=none -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -netdev tap,fd=25,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:68:7f:17,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -vnc 127.0.0.1:1 -vga cirrus -device AC97,id=sound0,bus=pci.0,addr=0x4 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5
char device redirected to /dev/pts/8
qemu: could not open disk image /var/lib/libvirt/images/netboot.img: Permission denied
2011-02-15 19:21:31.841: shutting down


Expected results:
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=vnc ...... like record in guest.log , and could hear the sound from vnc 

Additional info:
for spice , QEMU_AUDIO_DRV=spice could be set correctly