libvirt users - May 2013 - Help: Using Pre-created tap interfaces with Libvirt+Xen

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'>

<name>raghu_12345</name>
<uuid>12113325-d948-4a1b-b673-888a16b90726</uuid>
<memory>1048576</memory>
<vcpu>1</vcpu>


<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<boot dev='hd'/>
</os>

<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>

<features>
<pae/>
<acpi/>
<apic/>
</features>


<devices>
<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
<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'/>
</interface>
<disk type='file' device='disk'>
<source file='~/tmp/lucid.img'/>
<target dev='hda'/>
</disk>
<console type='pty'>
<target port='0'/>
</console>
<graphics port='-1' type='vnc' autoport='yes'
listen='0.0.0.0'/>
</devices>

</domain>


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.

Regards
Raghu
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