[Xen-devel] Attaching pre created tap interfaces to a VM in Xen for Routed Networking

[Raghu Nallamothu <raghu.nallamothu@xxxxxxxxx>]

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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