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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Dec 03, 2020 at 07:11:17AM -0500, Michael S. Tsirkin wrote:
> On Thu, Dec 03, 2020 at 11:43:41AM +0000, Dr. David Alan Gilbert wrote:
> > Another way to solve this would be to remove the unplugging from the
> > migration layer and leave it as a problem for the management layer to do
> > the unplug.
> 
> Daniel described the problem with modular management tools which expect
> pausing or slowing down guest to cause migration to converge.
> 
> Point is, it actually *will* make it converge but only if you
> pause it after unplug.
> 
> As it is, these tools fundamentally can not handle failover
> requiring guest cooperation. Moving code between layers won't help.
> Introducing failure modes as this patch does won't help either
> especially since Daniel wrote there are countless tools like this.
> We just break them all but have no resources to fix them,
> this does not help at all.
> 
> We can just leave the situation as is.
> 
> Or if we do want to be nice to these tools, how about we
> unpause the guest until unplug, then pause it again?
> This actually addresses the problem instead of
> shifting the blame, does it not?

This is a very bad idea because it changes the execution status of the
guest behind the apps/admins back, and that cannot be assumed to be a
safe thing todo.

Regards,
Daniel
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