Re: [Qemu-devel] pause and restore function before and after QEMU Live Snapshot

[Andrey Korolyov]

On Thu, Jul 17, 2014 at 1:48 AM, Yuanzhen Gu <address@hidden> wrote:
> Thanks very much Andrey!
>
> how can I figure out whether fsfreeze not succeed while taking snapshot, if
> I run a simple application inside VM, say mysql? thanks!
>
> Best,
> Yuanzhen
>
>
> On Wed, Jul 16, 2014 at 5:25 PM, Andrey Korolyov <address@hidden> wrote:
>>
>> On Thu, Jul 17, 2014 at 1:18 AM, Eric Blake <address@hidden> wrote:
>> > On 07/16/2014 03:13 PM, Yuanzhen Gu wrote:
>> >> Hi folks,
>> >>
>> >>
>> >> I am going to make a patch, and need to find the pause and
>> >> thaw(restore)
>> >> function before and after taking Live QEMU Snapshot respectively.
>> >
>> > Libvirt has the ability to do just that, when taking external disk-only
>> > snapshots.  You can turn on libvirt debugging to trace what QMP/agent
>> > commands are sent during the overall snapshot operation.
>> >
>> >>
>> >>
>> >>  Basically, I'm using # (qemu) snapshot_blkdev <blockX>
>> >> <snapshot-file><format> taking snapshot,
>> >> http://wiki.qemu.org/Features/Snapshots    my profile tool didn't work
>> >> when
>> >> giving command inside QMP.
>> >>
>> >>
>> >>  Does anyone know how to find the pause (freeze) and restore(thaw)
>> >> function
>> >> before and after taking snapshot? Or anyway using snapshot_blkdev
>> >> command
>> >> outside QEMU console? Thanks a lot in advance!
>> >
>> > You have to coordinate multiple commands: freeze to the guest agent,
>> > then snapshot to QMP, then thaw to the guest agent.
>> >
>> > --
>> > Eric Blake   eblake redhat com    +1-919-301-3266
>> > Libvirt virtualization library http://libvirt.org
>> >
>>
>> Just 2c:
>>
>> fsfreeze will not succeed if there are any container instances, for
>> example Docker, running in the VM on same filesystem. This exact case
>> can be fixed by extending agent` logic but it looks that the putting a
>> note is enough.
>>
>

Just non-zero exit code from agent`s operation, not matter if you
communicating directly via json exchange or via libvirt.