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Re: [Qemu-devel] [PATCH v9 07/11] block: Add QMP support for streaming t

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH v9 07/11] block: Add QMP support for streaming to an intermediate layer
Date: Tue, 3 May 2016 15:18:39 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 03.05.2016 um 14:53 hat Alberto Garcia geschrieben:
> On Fri 29 Apr 2016 05:11:07 PM CEST, Kevin Wolf wrote:
> >> +    if (active == NULL) {
> >> +        error_setg(errp, "Cannot find top level node for '%s'", device);
> >> +        goto out;
> >> +    }
> >
> > Hm... On the one hand, I really like that you don't expect the user to
> > provide the active layer in QMP. This allows us to remove this wart
> > once we have the new op blockers.
> Exactly, I still plan to stick to the API we discussed last year.
> > On the other hand, this code assumes that there is only a single
> > top-level node. This isn't necessarily true any more these days.
> Hmm... if you give me an example I can test that scenario.

Simply reference the same node twice:

$ x86_64-softmmu/qemu-system-x86_64 \
-drive if=none,file=/tmp/backing.qcow2,id=backing \
-drive file=/tmp/test.qcow2,backing=backing,id=hda \
-drive file=/tmp/test2.qcow2,backing=backing,id=hdb

If backing.qcow2 has another backing file, you can do the intermediate
streaming to it and both hda and hdb are active layers on top of it.


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