Re: [Qemu-devel] tcmu-runner and QEMU

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Sep 02, 2014 at 05:20:55PM -0700, Andy Grover wrote:
> On 09/02/2014 02:25 AM, Stefan Hajnoczi wrote:
> > The qemu-lio tool would live in the QEMU codebase and reuse all the
> > infrastructure.  For example, it could include a QMP monitor just like
> > the one you are adding to qemu-nbd.
> 
> Benoit and I talked a little about QMP on another part of the thread... I
> said I didn't think we needed a QMP monitor in qemu-lio-tcmu, but let me
> spin up on qemu a little more and I'll be able to speak more intelligently.

The QEMU block layer has useful features that are available as QMP
commands:

For example, the drive-mirror QMP command copies a disk image to a new
location while still servicing I/O requests.  This is used when an
administrator needs to migrate disk images to a new file system or
storage devices without downtime.

There are other commands for snapshots and backup which are issued via
QMP.

It might even make sense to make the tcmu interface available at
run-time in QEMU like the run-time NBD server.  This allows you to get
at read-only point-in-time snapshots while the guest is accessing the
disk.  See the nbd-server-start command in qapi/block.json.

Stefan

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