Re: [libvirt-users] KVM -snapshot mode

On 03/17/2014 11:51 AM, chris 0 wrote: We do NOT want to expose qemu's -snapshot parameter directly via libvirt, for several reasons: 1. it makes qemu use $TMPDIR, and on systems where $TMPDIR defaults to /tmp and where /tmp is not backed by disk, it can easily exhaust space limits in /tmp 2. -snapshot mode makes a guest non-migrateable 3. -snapshot is incompatible with sVirt SELinux labeling, because qemu ends up creating the file, but under sVirt rules, qemu is only allowed to use pre-existing pre-labeled files However, we DO plan on supporting transient disks (which is the underlying operation being provided by -snapshot mode), just by doing the work ourselves instead of letting qemu do it (that is, we'd create our OWN qcow2 wrapper, pass that to qemu, and then tear down the wrapper when the guest exits). In fact, we already designed the XML for it (under any <disk> that you want to be in snapshot mode, add a <transient/> tag) - we just haven't wired it up for qemu guests yet. To do that, we need to track the FULL backing chain in use by any domain, and _that's_ something that I'm actively working on. We'd also like to have a way to associate a storage pool per domain, so that actions that carve out what may be a large file will do so in the appropriate location; I'm not sure if anyone is currently working on coding this, although the idea has been around on the list for a while, and I'm more than willing to give design pointers to whoever tackles it. For more background, see https://bugzilla.redhat.com/show_bug.cgi?id=832194 -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org