[fedora-virt] fc12 virsh tap networking problem

[Chiradeep Vittal]

Hi,
On a fresh FC12 system, I am able to create and run KVM-based vms with tap networking
using the qemu-kvm command line but not using virsh.
I have user and group set to "root" in /etc/libvirt/qemu.conf. "user mode
networking" works with virsh, but not tap! selinux is disabled. 

I have this xml:
<domain type='kvm'>
  <name>centos</name>
  <uuid>22d9d573-d82c-c18d-36c0-d3ffef057468</uuid>
  <memory>131072</memory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64'>hvm</type>
  </os>
  <features>
    <acpi/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <devices>
    <emulator>/usr/bin/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/var/lib/images/centos.5-4.x86-64/centos-small.img'/>
      <target dev='hda' bus='ide'/>
    </disk>
    <interface type='user'>
      <mac address='52:54:00:7e:5b:58'/>
    </interface>
    <interface type='ethernet'>
      <mac address='52:54:00:2e:33:c8'/>
      <script path='/var/lib/images/centos.5-4.x86-64/qemu-ifup'/>
    </interface>
    <graphics type='vnc' port='5910' autoport='no'
listen=''/>
  </devices>
</domain>

This won't start even when I execute virsh as root:
[root@fc12 centos.5-4.x86-64]# virsh -c qemu+unix:///system   create domr.xml 
error: Failed to create domain from domr.xml
error: monitor socket did not show up.: No such file or directory
[root@fc12 centos.5-4.x86-64]# tail -3 /var/log/libvirt/qemu/centos.log 
LC_ALL=C
PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none
/usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1 -name centos -uuid
22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on
-net nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net
user,vlan=0,name=user.0 -net
nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0
-serial none -parallel none -usb -vnc :10 -vga cirrus 
warning: could not configure /dev/net/tun: no virtual network emulation
qemu: Could not initialize device 'tap'

'***** But I can execute the same command line and it works!!********
[root@fc12
centos.5-4.x86-64]# LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin
QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1 -name
centos -uuid 22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on
-net nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net
user,vlan=0,name=user.0 -net
nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0
-serial none -parallel none -usb -vnc :10 -vga cirrus &
[2] 4543

[root@fc12 centos.5-4.x86-64]# ps -ef | grep qemu
root      4543  3449  0 19:02 pts/12  
00:00:00 /usr/bin/qemu-kvm -S -M pc-0.11 -m 128 -smp 1 -name centos
-uuid 22d9d573-d82c-c18d-36c0-d3ffef057468 -monitor
unix:/var/lib/libvirt/qemu/centos.monitor,server,nowait -boot c -drive
file=/var/lib/images/centos.5-4.x86-64/centos-small.img,if=ide,index=0,boot=on
-net nic,macaddr=52:54:00:7e:5b:58,vlan=0,name=nic.0 -net
user,vlan=0,name=user.0 -net
nic,macaddr=52:54:00:2e:33:c8,vlan=1,name=nic.1 -net
tap,script=/var/lib/images/centos.5-4.x86-64/qemu-ifup,vlan=1,name=tap.0
-serial none -parallel none -usb -vnc :10 -vga cirrus