[libvirt] sending openvswitch "port db" info during libvirt migration

[Kyle Mestery (kmestery)]

On Aug 8, 2012, at 9:49 AM, Daniel P. Berrange wrote:
> On Tue, Aug 07, 2012 at 03:50:20PM -0400, Laine Stump wrote:
>> Someone asked on IRC the other day about sending openvswitch per-port
>> data (normally stored in the switch) to the destination host during a
>> migration. I suggested maybe this could be handled by encoding the
>> information into the interface's <virtualport> prior to migration, and
>> then writing it back out to openvswitch on the destination when the
>> interface was reconnected there.
>> 
>> I think there's a problem with that, though - they don't want to save
>> the port data on the source until the instant that the interface is
>> disconnected (since it is constantly changing), but by then the domain
>> XML has already long ago been formatted and sent to the destination.
>> 
>> So is there some other way within the confines of the current migration
>> protocol that this information can be sent from migration source to
>> destination?
> 
> I'd be interested to know more about just what sort of data it is that
> needs to be passed around. From what you describe though, the only
> way to pass that info would be to store it in the migration cookie
> when the 'Perform' step completes (ie QEMU now paused, no network
> I/O taking place), whereupon it will be passed into the 'Finish'
> step on the dest (which can set it and then resume QEMU)
> 
This is per-port data, tied to the specific virtual port associated with the VM
itself. This data is stored in the OVS DB, and is used/could be used by an
entity controlling Open vSwitch on the host. For example, stats may be kept
here.

>From what you indicate above, can you point me at the code which handles the
migration cookie?

Thanks!
Kyle

> 
> Daniel