Description of problem:

Description of Problem:
"virsh attach-interface" succeeds with the following message even if an already attached target device is specified.

# virsh attach-interface <domain-name> bridge br0 --target vnet0

Interface attached successfully

vnet0 is just an already attached target device. It should report an error
message like "vnet0 already attached" then. We believe that this is a bug of
"virsh attach-interface". Could you please fix "virsh attach-interface" so
that it reports an error message in the above case?

Version-Release number of selected component (if applicable):

Red Hat Enterprise Linux Version Number: 6
Release Number: snapshot13
Architecture: x86_64
Kernel Version: kernel-2.6.32-70.el6.x86_64
Related Package Version: libvirt-client-0.8.1-27.el6.x86_64 
How reproducible:


Steps to Reproduce:

1 - # virsh dumpxml rhel6
....
....
 <interface type='bridge'>
      <mac address='52:54:00:73:00:0e'/>
      <source bridge='br0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </interface>
....
....

# virsh attach-interface rhel6 bridge br0 --target vnet0
Interface attached successfully

It should say the interface is already attached.
 
Actual results:

Hotplugging and already attached network interface is successful.

Expected results:

Hot plugging an already attahced network interface should fail with an error message "interface already attached"

Additional info: