Description of problem:


Version-Release number of selected component (if applicable):
libvirt-0.9.4-12.el6.x86_64
qemu-kvm-0.12.1.2-2.192.el6.x86_64
kernel-2.6.32-197.el6.x86_64


How reproducible:
always

Steps to Reproduce:
1. install guest with tree  RHEL5.7-Server-20110622.0
2. start the guest
3. try to attach interface to guest with following two commands
   a.   # virsh attach-interface rhel57-new network default vnet0 --model e1000
   b.   # virsh attach-device rhel57-new interface.xml
        # cat interface.xml
        <interface type='bridge'>
           <source bridge='virbr0'/>
           <model type='virtio'/>
        </interface>

Actual results:
both of the two commands got success to attach the interface to rhel5u7 guest , but without reboot the guest , guest won't recognize the interface automatically
Besides, after shutdown guest, attached device xml won't be removed from guest xml file. 

Expected results:
guest can recognize attached interface automatically without reboot .

Additional info:
rhel6 guest won't encounter this problem . 
And for rhel5u7 guest, attach virtio disk device doesn't work as well .