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Re: [Qemu-devel] [PATCH 28/47] qmp: add drive-mirror command

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 28/47] qmp: add drive-mirror command
Date: Tue, 31 Jul 2012 11:33:52 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1

Il 31/07/2012 11:26, Kevin Wolf ha scritto:
> Am 24.07.2012 13:04, schrieb Paolo Bonzini:
>> This adds the monitor commands that start the mirroring job.
>> Signed-off-by: Paolo Bonzini <address@hidden>
> [ Moving the discussion upstream ]
>> Why make all of it inaccessible?  Everything except target device access
>> does have a stable API.  The target device access can be delayed to 1.3,
>> together with the much-needed QMP schema introspection.
> I'm not even sure about the QMP mirror command itself.
> I don't really like it, it does too many things at once: It can create
> the target image file, it opens the target and it actually starts the
> mirroring. It's rather bad at the first two steps, because it doesn't
> take any options. This means that it can't create qcow2v3 images, for
> example. Or you can't mirror into a backup with cache=unsafe while
> running your real VM on cache=writethrough.

Yes, though this can be worked around with mode: 'existing'.

> Having an all-in-one mirror command is a nice feature for HMP, but for
> QMP it's more like a design problem.
> Now I see you have called it drive-mirror

I thought this was your idea. :)

> , so that kind of implies that
> it's not the final blockdev-mirror but just a QMP version of a command
> primarily designed for HMP. As such this restricted functionality may be
> acceptable, but it's not like everything is already perfect and there's
> no room for discussion.

We keep going back to the same point that we do not have -blockdev, but
it's becoming a bit frustrating to always rehash this same point...


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