Re: [PATCH 2/2] failover: don't allow to migrate a paused VM that needs PCI unplug

[Michael S. Tsirkin]

On Tue, Nov 02, 2021 at 06:06:51PM +0100, Laurent Vivier wrote:
> On 02/11/2021 16:04, Michael S. Tsirkin wrote:
> > On Wed, Sep 29, 2021 at 04:43:11PM +0200, Laurent Vivier wrote:
> > > As the guest OS is paused, we will never receive the unplug event
> > > from the kernel and the migration cannot continue.
> > > 
> > > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > 
> > Well ... what if user previously did
> > 
> > pause
> > start migration
> > unpause
> > 
> > we are breaking it now for no good reason.
> > 
> > Further, how about
> > 
> > start migration
> > pause
> > 
> > are we going to break this too? by failing pause?
> > 
> > 
> 
> TL;DR: This patch only prevents to migrate a VFIO device as failover allows
> to start a migration with a VFIO device plugged in.
> 
> Long Story:
> 
> * before this patch:
> 
> - pause and start migration and unpause-> fails if we unpause too late
> because we migrate a VFIO device, works otherwise


confused about this one. can you explain pls?

> - start migration and pause before we unplug the card -> hangs forever
> - start migration and pause after we unplug the card -> it works fine
> 
> * After this patch:
> 
> - pause and start migration and unpause-> fails if we unpause too late
> because of the new error checking, works otherwise
> - start migration and pause before we unplug the card -> fails because of
> the new error checking
> - start migration and pause after we unplug the card -> it works fine
> 
> Thanks,
> Laurent
>