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

[Kevin Wolf]

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.

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, 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.

Kevin