Description of problem:
If I have QEMU/KVM guest started in libvirtd and then restart libvirtd, libvirtd no longer knows mapping between guests and tun devices on host and quering virDomainInterfaceStats do not work.


Version-Release number of selected component (if applicable):
libvirt version 0.7.1 (Fedora 12 rpm: libvirt-0.7.1-15.fc12.x86_64)

also tested with Centos 5.4 and libvirt 0.6.3

How reproducible:
every time

Steps to Reproduce:
1. Start QEMU/KVM guest with: virsh start vm01
2. restart libvirtd: /sbin/service libvrtd restart
3. Get statistics with virsh domifstat vm01 vnet0
  
Actual results:
[root@kvm01 ~]# virsh domifstat vm01 vnet0
error: Failed to get interface stats vm01 vnet0
error: invalid argument in invalid path, 'vnet0' is not a known interface


Expected results:
[root@kvm01 ~]# virsh domifstat vm01 vnet0
vnet0 rx_bytes 83980
vnet0 rx_packets 1612
vnet0 rx_errs 0
vnet0 rx_drop 0
vnet0 tx_bytes 3546
vnet0 tx_packets 15
vnet0 tx_errs 0
vnet0 tx_drop 0


Additional info:
I found out that after libvirtd forgets mapping for virtual interfaces. Here are the output from virsh dumpxml vm01 before restart:
    <interface type='network'>
      <mac address='52:54:00:28:59:5c'/>
      <source network='default'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
    </interface>

and after restart of libvirtd:
    <interface type='network'>
      <mac address='52:54:00:28:59:5c'/>
      <source network='default'/>
      <model type='virtio'/>
    </interface>

the <target dev='vnet0'/>  is missing.