On Thu, Jan 11, 2018 at 01:46:38PM +0100, Max Reitz wrote: > On 2018-01-08 14:52, Eric Blake wrote: > > On 01/07/2018 06:23 AM, Richard Palethorpe wrote: > >> Add QAPI wrapper functions for the existing snapshot functionality. These > >> functions behave the same way as the HMP savevm, loadvm and delvm > >> commands. This will allow applications, such as OpenQA, to programmatically > >> revert the VM to a previous state with no dependence on HMP or qemu-img. > > > > That's already possible; libvirt uses QMP's human-monitor-command to > > access these HMP commands programmatically. > > > > We've had discussions in the past about what it would take to have > > specific QMP commands for these operations; the biggest problem is that > > these commands promote the use of internal snapshots, and there are > > enough performance and other issues with internal snapshots that we are > > not yet ready to commit to a long-term interface for making their use > > easier. At this point, our recommendation is to prefer external snapshots. > > We already have QMP commands for internal snapshots, though. Isn't the > biggest issue that savevm takes too much time to be a synchronous QMP > command?
Ultimately savevm/loadvm are using much of the migration code internally, but are not exposed as URI schemes. Could we perhaps take advantage of the internal common layer and define a migration URI scheme snapshot:<name> where '<name>' is the name of the internal snapshot in the qcow2 file. Then you could just use the regular migrate QMP commands for loading and saving snapshots. Might need a little extra work on the incoming side, since we need to be able to load snapshots, despite QEMU not being started with '-incoming defer', but might still be doable ? This would theoretically give us progress monitoring, cancellation, etc for free. 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 :|
