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Date: Wed, 22 May 2013 18:11:50 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting
 Disk Introspection
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To: Wolfgang Richter <wolf@cs.cmu.edu>
Cc: "Richard W.M. Jones" <rjones@redhat.com>, stefanha <stefanha@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

Il 22/05/2013 17:51, Wolfgang Richter ha scritto:
> On Thu, May 16, 2013 at 9:44 AM, Richard W.M. Jones <rjones@redhat.com
> <mailto:rjones@redhat.com>> wrote:
> 
>     Ideally I'd like to issue some QMP commands which would set up the
>     point-in-time snapshot, and then connect to this snapshot over (eg)
>     NBD, then when I'm done, send some more QMP commands to tear down the 
> 
>     snapshot.
> 
> 
> This is actually interesting.  Does the QEMU nbd server support multiple
> readers?

Yes.

> Essentially, if you're RWMJ (not me), and you're keeping a full
> mirror, it's clear that the mirror write stream goes to an nbd server,
> but is it possible to attach a reader to that same nbd server and read
> things back (read-only)?

Yes, it can be done with both qemu-nbd and the QEMU nbd server commands.

Paolo