Re: qemu-rbd : savevm monitor command don't save vmstate, is it normal ?

[Josh Durgin <josh.durgin@inktank.com>]

On 08/29/2012 06:40 AM, Alexandre DERUMIER wrote:
> Hi,
>
> I'm trying to take a full vm state snapshot with savevm monitor command  (qemu 0.12rc1 + rbd 0.48.1)
>
> it seem that vmstate is not saved in the snapshot. (I also don't notice any vm hang during snapshot)
> Snapshot of disk is correctly made.

AFAIK the only block backend that supports saving the vmstate is qcow2.
For rbd, the savevm/loadvm monitor commands are equivalent to
'rbd snap create' and 'rbd snap rollback'. They just save/rollback the
disk.

> using loadvm monitor command, rollback correctly to disk snapshot but vm hang.

If you don't quiesce i/o i.e. via xfsfreeze (it works on the vfs level
now, so it's not xfs-specific anymore) before snapshotting a running
vm, the fs might require a fsck to be usable. This is only rolling back
the disk, and not the memory state, so doing it while the vm is running
is likely to cause problems.

> starting qemu with -loadvm snapshotname give
> kvm: Error -22 while loading VM state
>
>
> Is it normal ? Not implemented ?

bdrv_{save|load}_vmstate are not implemented.

>
> Regards,
>
> Alexandre