On Thu, Apr 15, 2021 at 12:04 PM Daniel P. Berrangé <berra...@redhat.com> wrote: > > On Thu, Apr 15, 2021 at 05:44:02PM +0200, Vitaly Kuznetsov wrote: > > When a migration blocker is added nothing is reported to the user, > > inability to migrate such guest may come as a late surprise. As a bare > > minimum, we can print a warning. To not pollute the output for those, who > > have no intention to migrate their guests, introduce '--no-migration' > > option which both block the migration and eliminates warning from > > I wonder how this is actually going to work in practice ? > > At the time libvirt starts a guest, it has no idea whether the guest > is likely to need migration 3, 6, 12, 24 months in to the future.
I believe the libvirt API could be extended so applications can indicate that migration is not a required feature. This would let QEMU automatically enable useful but non-migration-friendly features. For example, I would expect "-cpu host" to become the default CPU model if --no-migration is specified. > > IOW, we can't use a --no-migration flag and will be stuck with these > warnings no mtter what. The expected behavior of the libvirt API is to create migratable VMs by default, isn't it? This means it would be valid for libvirt to use "--only-migratable" by default. If libvirt can't use "--only-migratable" by default, I would say it's a deficiency of the libvirt API that needs to be addressed. > > Is it possible to query the migration blockers via QMP ? I don't think it is, but we can add that if it's useful for libvirt. > > Libvirt recently introduced a new API 'virDomainGetMessages' which > lets us report a list of human targetted message strings against > a guest. We use it for reporting when an operation has tainted > a guest, and also use it for reporting when a deprecated QEMU > feature is used. We could use it to report any migration > blockers that exist. > > These are visible from 'virsh dominfo $guestname' and could also > be displayed by a mgmt application. Cool! Will the API include all warnings printed by QEMU to stderr? > > NB, the messages are intentionally declared opaque strings, so > mgmt apps shouldn't try to parse them. They merely know whether > the count is non-zero for any given message class. > > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > -- Eduardo
