* Peter Krempa (pkrempa@xxxxxxxxxx) wrote: > On Mon, Jun 04, 2018 at 16:51:18 +0200, Jiri Denemark wrote: > > Libvirt relies on being able to kill the destination domain and resume > > the source one during migration until we called "cont" on the > > destination. Unfortunately, QEMU automatically activates block devices > > at the end of migration even when it's called with -S. This wasn't a big > > issue in the past since the guest is not running and thus no data are > > written to the block devices. However, when QEMU introduced its internal > > block device locks, we can no longer resume the source domain once the > > destination domain already activated the block devices (and thus > > acquired all locks) unless the destination domain is killed first. > > > > Since it's impossible to synchronize the destination and the source > > libvirt daemons after a failed migration, QEMU introduced a new > > migration capability called "late-block-activat" which ensures QEMU > > won't activate block devices until it gets "cont". The only thing we > > need to do is to enable this capability whenever QEMU supports it. > > I'm wondering when this new feature should _not_ be used. I did not get > the information from the qemu commit message so I've cc'd David to shed > some light. > > If it's desired to always pass it then I'm failing to see why they've > added it in the first place. There was some worry that doing it by default would be a subtle API change; personally I didn't really see it as a problem, but since people were worried I made it switchable. See: https://lists.gnu.org/archive/html/qemu-devel/2018-04/msg01300.html Dave -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
