Re: [Qemu-devel] [PATCH 1/4] migration: allow unplug during migration for failover devices

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

On Tue, May 21, 2019 at 10:33:36AM +0100, Dr. David Alan Gilbert wrote:
> * Jens Freimann (jfreimann@redhat.com) wrote:
> > In "b06424de62 migration: Disable hotplug/unplug during migration" we
> > added a check to disable unplug for all devices until we have figured
> > out what works. For failover primary devices qdev_unplug() is called
> > from the migration handler, i.e. during migration.
> > 
> > This patch adds a flag to DeviceState which is set to false for all
> > devices and makes an exception for vfio-pci devices that are also
> > primary devices in a failover pair.
> > 
> > Signed-off-by: Jens Freimann <jfreimann@redhat.com>
> 
> So I think this is safe in your case, because you trigger the unplug
> right at the start of migration during setup and plug after failure;
> however it's not generally safe - I can't unplug a device while the
> migration is actually in progress.

Libvirt will also block any attempt to hotplug/unplug device during
migration.


Regards,
Daniel
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