On Mon, Dec 13, 2010 at 10:00:48PM -0700, Alex Williamson wrote: > On Tue, 2010-12-14 at 06:43 +0200, Michael S. Tsirkin wrote: > > On Mon, Dec 13, 2010 at 12:15:08PM -0700, Alex Williamson wrote: > > > On Mon, 2010-12-13 at 21:06 +0200, Michael S. Tsirkin wrote: > > > > On Mon, Dec 13, 2010 at 11:59:16AM -0700, Alex Williamson wrote: > > > > > On Mon, 2010-12-13 at 20:54 +0200, Michael S. Tsirkin wrote: > > > > > > On Mon, Dec 13, 2010 at 11:00:44AM -0700, Alex Williamson wrote: > > > > > > > On Mon, 2010-12-13 at 19:50 +0200, Michael S. Tsirkin wrote: > > > > > > > > On Mon, Dec 13, 2010 at 10:43:22AM -0700, Alex Williamson wrote: > > > > > > > > > So, unfortunately, I stand by my original patch. > > > > > > > > > > > > > > > > What about the one that put -1 in saved index for a hotplugged > > > > > > > > device? > > > > > > > > > > > > > > There are still examples that don't work even without hotplug > > > > > > > (example 2 > > > > > > > and example 3 after the reboot). That hack limits the damage, > > > > > > > but still > > > > > > > leaves a latent bug for reboot and doesn't address the non-hotplug > > > > > > > scenarios. So, I don't think it's worthwhile to pursue, and we > > > > > > > shouldn't pretend we can use it to avoid bumping the version_id. > > > > > > > Thanks, > > > > > > > > > > > > > > Alex > > > > > > > > > > > > I guess when we bump it we tell users: migration is completely > > > > > > borken to the old version, don't even try it. > > > > > > > > > > > > Is there a way for libvirt to discover such incompatibilities > > > > > > and avoid the migration? > > > > > > > > > > I don't know if libvirt has a way to query this in advance. If a > > > > > migration is attempted, the target will report: > > > > > > > > > > savevm: unsupported version 5 for '0000:00:03.0/rtl8139' v4 > > > > > > > > > > And the source will continue running. We waste plenty of bits getting > > > > > to that point, > > > > > > > > Yes, this happens after all of memory has been migrated. > > > > > > Better late than never :^\ > > > > One other question: can we do the same by creating a new (empty) > > section? As was discussed in the past this is easier for > > downstreams to cherry-pick. > > The only way I can think to do that would be to have a subsection that > is always included, but saves no data. That would force a failure on > new->old migration, but I don't think it really matches the intended > purpose of subsections and feels like it's adding cruft for no gain. > Maybe I'm missing something. Juan, is there any advantage to trapping > this in a subsection? Thanks, > > Alex
Maybe in this particular case the advantage is minimal. But it seems easier to stick to a rule of no more version bumps than argue about each case. -- MST
