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

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.