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

[Wolfgang Richter]

On Thu, May 16, 2013 at 9:44 AM, Richard W.M. Jones <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?

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)?  I know it's possible to name

the volumes you attach to, so I think conceptually with the nbd protocol this should work. 

I think this document would be better with one or more examples
showing how this would be used.

I think the thread now has me looking at making the mirror command 'active' :-)

rather than have a new QMP command.

--
Wolf