libvirt users - Jul 2011 - KVM and <interface type='ethernet'>

Hi!

I'm trying to set up a VM with "just an tap device" with the
following config
(basicly inherited from 'virsh domxml-from-native qemu-argv'):

<domain type='kvm'>
[...]
    <interface type='ethernet'>
      <mac address='52:54:1f:ac:08:51'/>
      <target dev='foo_eth0'/>
      <model type='virtio'/>
    </interface>
[...]
  </devices>
</domain>

This sadly failes with:

| error: Failed to start domain foo
| error: internal error process exited while connecting to monitor: could not
configure /dev/net/tun: Device or resource busy

I'm wondering why this fails as there shouldn't anything be done with
the tap device besides setting it up.

(The basic goal would be to set up a VM with a tap device, put an v4
 and v6 IP on it and let OSPF do the rest. As the <script> parameter
 will not work with dropped privileges I wrote a wrapper for the kvm
 binary which takes care of this via sudo. This part works, but I fail
 to get the VM started with <interface type='ethernet'>)

Any ideas?

Thanks
Max
-- 
<@uschebit> Das erkl?rt die Sitte. Das ist so ?hnlich wie mit dem
Verbeugen zur Begr??ung in Japan.
            Das dient auch nur dazu, durch Begutachten der Schuhqualit?t den
sozialen Rang festzustellen.