Hi All., 
         I am not sure if this is possible in xen via Libvirt, but what I am trying to do is, I want libvirt to launch a VM and attach a pre-created tap interface to that VM ( I do not want XEN to create one, as I am running a lot of custom scripts on my tap interface). I also dont want xen to attach this tap interface to a bridge.

For example, lets say I have created a tap interface with name "tap123456" when libvirt launches my VM in xen, I want the VM to read its networking info from this tap interface. 

But I wasn't so successful in doing this when ever I am trying to do this, I am seeing the following error message "VmError: Device 0 (vif) could not be connected. Hotplug scripts not working." and "error: POST operation failed: xend_post: error from xen daemon: (xend.err 'Device 0 (vif) could not be connected. Cannot rename interface vif4.0. An interface with name tap12345 already exists.')". But I dont want xen to create  another interface and rename it, rather want xen to use the existing one

=== output of lsmod ===

bash-4.1# lsmod | grep xen
xen_acpi_processor      4465  0 
xen_netback            25455  0 [permanent]
xen_gntdev              9504  2 
xen_evtchn              4899  3 
xenfs                   2943  1 
xen_privcmd             4972  19 xenfs

==== end of output ====

My Configuration : Centos 6.2 with Xen 4.2.5 along with Libvirt

Libvirt Configuration file, 

<domain type='xen'>


<boot dev='hd'/>



<interface type="ethernet">
<mac address='00:25:90:3f:25:91'/>  <!-- I want this mac to be mac address of a vm -->
<target dev='tap123456'/> 
<disk type='file' device='disk'>
<source file='~/tmp/lucid.img'/>
<target dev='hda'/>
<console type='pty'>
<target port='0'/>
<graphics port='-1' type='vnc' autoport='yes' listen=''/>


I have a pre-created  tap interface with name 'tap123456'  with all the networking setup with dhcp and dns running.

Thanks for your time and help.