[libvirt PATCH 4/4] qemu: Enable migration events only for fresh QEMU process

Daniel P. Berrangé berrange at redhat.com
Thu May 12 11:39:03 UTC 2022


On Thu, May 12, 2022 at 10:55:47AM +0200, Jiri Denemark wrote:
> Every running QEMU process we are willing to reconnect (i.e., at least
> 3.1.0) supports migration events and we can assume the capability is
> already enabled since last time libvirt daemon connected to its monitor.
> 
> Well, it's not guaranteed though. If libvirt 1.2.17 or older was used to
> start QEMU 3.1.0 or newer, migration events would not be enabled. And if
> the user decides to upgrade libvirt from 1.2.17 to 8.4.0 while the QEMU
> process is still running, they would not be able to migrate the domain
> because of disabled migration events. I think we do not really need to
> worry about this scenario as libvirt 1.2.17 is 7 years old while QEMU
> 3.1.0 was released only 3.5 years ago. Thus a chance someone would be
> running such configuration should be fairly small and a combination with
> upgrading 1.2.17 to 8.4.0 (or newer) with running domains should get it
> pretty much to zero. The issue would disappear ff the ancient libvirt is
> first upgraded to something older than 8.4.0 and then to the current
> libvirt.

libvirt 1.2.17 was released in Jul 2015

QEMU 3.1.0 was released in Dec 2018

New QEMU has periodically introduced CLI changes that made it
incompatible with older libvirt.

Given that 3+1/2 year gap, I feels like there is a pretty decent
chance that it was impossible to ever start QEMU 3.3.0 using
a libvirt 1.2.17.  If so, we don't have anything to worry about
from an upgrade POV


With regards,
Daniel
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