Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection

[Paolo Bonzini]

Il 22/05/2013 17:51, Wolfgang Richter ha scritto:
> On Thu, May 16, 2013 at 9:44 AM, Richard W.M. Jones <address@hidden
> <mailto:address@hidden>> 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