Thanks a lot Eric for taking the time to write such an in-depth reply! Kind Regards
Chris On Mon, Mar 17, 2014 at 6:06 PM, Eric Blake <[email protected]> wrote: > On 03/17/2014 11:51 AM, chris 0 wrote: > > Hi, > > > > I'm just wondering is there any way for me to trigger KVM's > > -snapshot parameter from libvirt. > > 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 > >
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