[libvirt] libvirt external disk-only snapshot will pause the VM?

[Yuanzhen Gu]

yes, I got your point, thanks very much Eric.

If I want to take a distributed snapshot, which need pause all the VMs and
then take snapshot, how can I control the pause for all the VMs?

Is there only way that I turn to freeze/thaw functions?

and freeze/thaw only for file systems, not for the whole guest, am I right?
   Thanks a lot!

Best,
Yuanzhen


On Wed, Aug 6, 2014 at 11:35 AM, Eric Blake <eblake at redhat.com> wrote:

> On 08/06/2014 08:36 AM, Yuanzhen Gu wrote:
>
> [please don't top-post on technical lists]
>
> > Thanks very much Eric!  This is exactly what I guessed, I just wondering
> > where I could find this piece of code and control the the pause time of
> > guest, while the snapshot being taken?  thanks !
>
> Actually, for new enough qemu (one with the 'transaction' QMP command),
> or for a guest where only one disk is being snapshotted, there is no
> pause required.  See qemuDomainSnapshotCreateDiskActiveExternal in
> src/qemu/qemu_driver.c.  When a pause is required, it is only for the
> fraction of a second required to issue a followup qemu QMP command to
> resume the guest, so there is no need for a knob to control the pause
> time (it is as already as fast as possible).
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
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