Re: [Qemu-devel] [RFC V3 7/7] qmp: Allow to take external snapshots on bs graphs node.

[Benoît Canet]

Le Wednesday 04 Dec 2013 à 17:11:26 (-0700), Eric Blake a écrit :
> On 12/03/2013 06:26 AM, Benoît Canet wrote:
> > Signed-off-by: Benoit Canet <address@hidden>
> > ---
> >  blockdev.c       | 49 +++++++++++++++++++++++++++++++++++++++++--------
> >  hmp.c            |  4 +++-
> >  qapi-schema.json | 13 ++++++++++---
> >  qmp-commands.hx  | 11 ++++++++++-
> >  4 files changed, 64 insertions(+), 13 deletions(-)
> > 
> 
> > 
> > +    if (has_node_name && !has_snapshot_node_name) {
> > +        error_setg(errp, "New snapshot node name missing");
> > +        return;
> > +    }
> 
> Why is it okay to omit the node name when passing a device name (which
> creates an anonymous node as the new root of the device tree) but not
> when passing a node name?  Are you trying to guarantee that all
> anonymous nodes can be reached from a device name, and that when taking
> a snapshot from a node name the new node is not necessarily tied to a
> device and must therefore be named?

Yes bs device living just under block backend will ever be accessible via device
whereas other bs really need a node-name to be set to be manipulated.
Also it avoid adding a new mandatory field for the device case which is good for
compatibility with previous versions.

Best regards

Benoît

> 
> > -# @device:  the name of the device to generate the snapshot from.
> > +# Either @device or @node-name must be set but not both.
> > +#
> > +# @device: #optional the name of the device to generate the snapshot from.
> > +#
> > +# @node-name: #optional graph node name to generate the snapshot from 
> > (Since 1.8)
> >  #
> >  # @snapshot-file: the target of the new image. A new file will be created.
> >  #
> > +# @snapshot-node-name: the graph node name of the new image (Since 1.8)
> 
> 2.0, also mark this one #optional
> 
> > +#
> >  # @format: #optional the format of the snapshot image, default is 'qcow2'.
> 
> Unrelated to this patch, but @format is another field worth turning into
> an enum instead of an open-coded string.
> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>