[ovs-discuss] Problem with OpenVswitch 1.0.0 database backend and persistent settings.

Todd Deshane deshantm at gmail.com
Sun May 23 00:26:48 UTC 2010


Comments inline.

On Fri, May 21, 2010 at 4:02 PM, Dan Wendlandt <dan at nicira.com> wrote:
> On Thu, May 20, 2010 at 1:47 AM, Mark Persohn
> <Mark.Persohn at superchoice.com.au> wrote:
>> I have looked at trying to run a script as prt of the VM startup but since
>> we are running libvirtd/qemu in bridge
>> mode it will not run scripts!
> I do not have any hands-on experience with libvirt and KVM, but from talking
> to other people who have used OVS with libvirt, I was under the impression
> that libvirt provides a mechanism by which you can bring up VM interface
> devices using an arbitrary script.
> The libvirt docs
> (http://libvirt.org/formatdomain.html#elementsNICSEthernet ) mention:
> Generic ethernet connection
> Provides a means for the administrator to execute an arbitrary script to
> connect the guest's network to the LAN. The guest will have a tun device
> created with a name of vnetN, which can also be overridden with the <target>
> element. After creating the tun device a shell script will be run which is
> expected to do whatever host network integration is required. By default
> this script is called /etc/qemu-ifup but can be overridden.
>   ...
>   <devices>
>     <interface type='ethernet'/>
>     ...
>     <interface type='ethernet'>
>       <target dev='vnet7'/>
>       <script path='/etc/qemu-ifup-mynet'/>
>     </interface>
>   </devices>
>   ...
> I am guessing such a script might let you override libvirt's mechanism for
> adding a VM interface device to the bridge and instead let you directly
> configure it using OVS (e.g., ovs-vsctl set port netwin0 tag=6 ).
> As I recall, you're not the first person to have this problem so however we
> end up resolving it, we should document this better on the OVS site.

I haven't explicitly tried libvirt + open vSwitch yet either, but I
had read this:

I did however run across this blog that gave me the idea to just put
the config in place in a "just in time" manner:

But, even though that trick works, it is clearly a hack. I think
libvirt will (if they haven't already) add support for gracefully
handling open vSwitch and similar things. Especially since qemu is
discussing supporting (maybe they already do support) various network
backends (vepa, vswitches, macvtap, etc.).

If someone tests explicitly whether libvirt supports the script option
or not please post the results to the list.


Todd Deshane

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