Re: [Qemu-devel] drive transactions (was Re: [PATCH 2/2 v2] Add the blockdev-reopen and blockdev-migrate commands)

[Anthony Liguori]

On 02/27/2012 09:03 AM, Paolo Bonzini wrote:
> On 02/27/2012 03:59 PM, Anthony Liguori wrote:
> > The problem is that the current commands are not designed well.  For
> > instance, multi-snapshot could look like:
> >
> > block-freeze ide0-hd0
> > block-freeze ide1-hd1
> > block-reopen ide0-hd0 my-new-file0.qcow2
> > block-reopen ide1-hd1 my-new-file1.qcow2
> > block-unfreeze ide1-hd1
> > block-unfreeze ide1-hd0
> >
> > This would work regardless of whether the commands were implemented
> > asynchronously within QEMU too.
>
> This looks good, too.  Positive: maps well to fsfreeze/thaw with help
> from the guest agent.  Negative: you have to specify the devices three
> times.  Overall, I think I like it.
>
> However, you need to add freeze/unfreeze capabilities to the block
> layer.  Not hard, but one more thing to do.

Right.  But it also generalizes to other QMP operations which is potentially 
interesting.

And providing mechanisms like this gives more flexibility to management tools to 
implement interesting features without constantly chancing new QMP commands.

Regards,

Anthony Liguori

> Paolo