Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest

[Daniel P . Berrangé]

On Wed, Dec 02, 2020 at 05:13:18AM -0500, Michael S. Tsirkin wrote:
> On Wed, Nov 18, 2020 at 09:37:22AM +0100, Juan Quintela wrote:
> > If we have a paused guest, it can't unplug the network VF device, so
> > we wait there forever.  Just change the code to give one error on that
> > case.
> > 
> > Signed-off-by: Juan Quintela <quintela@redhat.com>
> 
> It's certainly possible but it's management that created
> this situation after all - why do we bother to enforce
> a policy? It is possible that management will unpause immediately
> afterwards and everything will proceed smoothly.
> 
> Yes migration will not happen until guest is
> unpaused but the same it true of e.g. a guest that is stuck
> because of a bug.

That's pretty different behaviour from how migration normally handles
a paused guest, which is that it is guaranteed to complete the migration
in as short a time as network bandwidth allows.

Just ignoring the situation I think will lead to surprise apps / admins,
because the person/entity invoking the migration is not likely to have
checked wether this particular guest uses net failover or not before
invoking - they'll just be expecting a paused migration to run fast and
be guaranteed to complete.

Regards,
Daniel
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