From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44067) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eZcpG-0007rD-BL for qemu-devel@nongnu.org; Thu, 11 Jan 2018 08:23:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eZcpE-0003xk-So for qemu-devel@nongnu.org; Thu, 11 Jan 2018 08:23:22 -0500 Date: Thu, 11 Jan 2018 13:23:05 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20180111132304.GD2669@work-vm> References: <20180107122336.29333-1-richiejp@f-m.fm> <5cf19623-72ac-fb8b-2054-a60d42419ec6@redhat.com> <20180111130427.GG8326@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180111130427.GG8326@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/2] Add save-snapshot, load-snapshot and delete-snapshot to QAPI List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Max Reitz , Eric Blake , Richard Palethorpe , qemu-devel@nongnu.org, Qemu-block , quintela@redhat.com, armbru@redhat.com, rpalethorpe@suse.com * Daniel P. Berrange (berrange@redhat.com) wrote: > 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: > > where '' is the name of the internal snapshot in the qcow2 file. I had wondered about that; I'd just thought of doing the migration saving to a block device rather than the rest of the snapshot activity around it; but I guess that's possible. > 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. What actually stops this working other than the sanity check in migrate_incoming ? Dave > > > 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 :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK