On Wed, Oct 11, 2017 at 08:13:10PM +0100, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > Hi, > This set attempts to make a race condition between migration and > drive-mirror (and other block users) soluble by allowing the migration > to be paused after the source qemu releases the block devices but > before the serialisation of the device state. > > The symptom of this failure, as reported by Wangjie, is a: > _co_do_pwritev: Assertion `!(bs->open_flags & 0x0800)' failed > > and the source qemu dieing; so the problem is pretty nasty. > This has only been seen on 2.9 onwards, but the theory is that > prior to 2.9 it might have been happening anyway and we were > perhaps getting unreported corruptions (lost writes); so this > really needs fixing. > > This flow came from discussions between Kevin and me, and we can't > see a way of fixing it without exposing a new state to the management > layer. > > The flow is now: > > (qemu) migrate_set_capability pause-before-device on
How about 'switchover-cleanup' > (qemu) migrate -d ... > (qemu) info migrate > ... > Migration status: pause-before-device and 'switchover' > ... > << issue commands to clean up any block jobs>> > > (qemu) migrate_continue pause-before-device > (qemu) info migrate > ... > Migration status: completed > > This set has been _very_ lightly tested just at the normal migration > code, without the addition of the drive mirror; so this is a first > cut. I'd appreciate some feedback from libvirt whether the inteface > is OK and ideally a hack to test it in a full libvirt setup to see > if we hit any other issues. > > The precopy flow is: > active->pause-before-device->completed > > The postcopy flow is: > active->pause-before-device->postcopy-active->completed > > Although the behaviour with postcopy only gets interesting when > we add something like Max's active-sync. > > Please argue about the command and state naming. Argued above :-) 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 :|
