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Re: [Qemu-devel] [PATCH 1/4] migration: allow unplug during migration fo


From: Jens Freimann
Subject: Re: [Qemu-devel] [PATCH 1/4] migration: allow unplug during migration for failover devices
Date: Thu, 23 May 2019 10:01:09 +0200
User-agent: NeoMutt/20180716

On Tue, May 21, 2019 at 10:33:36AM +0100, Dr. David Alan Gilbert wrote:
* Jens Freimann (address@hidden) 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 <address@hidden>

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.

I tried to limit it to only allow it in failover case. You're saying
it's missing something and not strict enough? I could allow it only
during migration setup. I guess we'll need a similar exception for
failover in libvirt.
regards,
Jens


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