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

[Yuanzhen Gu]

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.