[. . .] On Fri, Sep 11, 2015 at 10:45:34AM -0600, Eric Blake wrote: > On 09/11/2015 10:18 AM, Jérôme wrote: > > >> Yep, that about covers it. Note that the --quiesce step in snapshot > >> creation requires qemu-guest-agent running in the guest, and that you > >> trust interaction with your guest. > > > > Yes, I think I get this. I don't really figure out what these cases > > could be. We're using Debian Jessie and I installed qemu-guest-agent. > > Other VM could use other systems, but most likely Linux based. > > qga with support for quiesce has also been ported to Windows guests. > > > > > Do you mean that, in cases where you shouldn't trust the guest, using > > '--quiesce' might end up being worse than nothing? Or just useless? > > If the agent is not running, using --quiesce will fail the entire > command; you'd learn pretty quickly to retry without --quiesce for > guests that don't know how to handle it. . But if the guest is > malicious, it can pretend to be a guest agent, but intentionally refuse > to reply to the --quiesce request, and leave libvirt hung waiting for a > reply. So it boils down to whether you trust your guests to be > reasonable with their guest agent connection (fine if it is your own > guests, not so much if you are hosting a cloud for other people's guests). > > > > >>> -> Anything wrong about my snapshot-create-as and blockcommit command > >>> lines? May I remove the snapshot with only a rm command? > >> > >> Looks correct to me, and matches my recent KVM Forum slides: > >> http://events.linuxfoundation.org/sites/events/files/slides/2015-qcow2-expanded.pdf > > > > I'll have a look at these, thanks. Yes, I highly recommend it. This talk gives an excellent under-the-hood details of virtual machine disk image backing chain management. Associated video: https://www.youtube.com/watch?v=etIGp12RHRE > The libvirt commands were towards the end, in part 3; but the first two > parts might give a better understanding of the overall operations of > what is happening. > > > >> virsh snapshot-delete --metadata $dom $badname > >> > >> to remove $badname snapshot that no longer exists because you changed > >> things behind the scenes. > > > > Before removing the .xml file, I tried the command indicated in the wiki > > [1] with no success. > > > > "NOTE-2: Optionally, you can also supply '--no-metadata' option to tell > > libvirt to not track the snapshot metadata -- this is useful currently > > as at a later point when you merge snapshot files, then you have to > > explicitly clean the libvirt metadata (by invoking: virsh > > snapshot-delete vm1 --delete --current -- repeat this as needed.)" > > > > Shouldn't the > > > > virsh snapshot-delete vm1 --delete --current > > > > be rephrased as > > > > virsh snapshot-delete vm1 --metadata --current > > Yep, sounds like a bug in the wiki, so I fixed it. Indeed, it was a typo. I didn't even notice it until now as I just type these commands from muscle memory. Thanks, Eric, for fixing it (and for all the detailed responses). -- /kashyap _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
