[libvirt-users] KVM -snapshot mode

[chris 0]

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 <eblake at redhat.com> 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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvirt-users/attachments/20140318/7ae21981/attachment.htm>