Re: [Qemu-devel] Adding an overlay with 'blockdev-add' fails with: "Parameter 'driver' is missing"

[Kashyap Chamarthy <kchamart@redhat.com>]

On Thu, Feb 23, 2017 at 04:11:21PM +0100, Markus Armbruster wrote:
> Kashyap Chamarthy <kchamart@redhat.com> writes:
> 
> > TL;DR: Using `blockdev-add` to create an overlay file succeeds with QEMU
> >        2.7.0, however the *same* test fails with QEMU from Git (plus a
> >        couple of patch series from mailing list).  Details below.
> 
> commit 0153d2f50bc2ad3f41810d838fcf66acbf10f07a
> Author: Kevin Wolf <kwolf@redhat.com>
> Date:   Fri Oct 7 17:05:04 2016 +0200
> 
>     block: Remove "options" indirection from blockdev-add

[...]

> Sorry for the confusion!  Early adopters always have the most fun ;)

Ah, I see, thanks for the pointer.

I tried to come up with the below JSON, after looking at the QAPI schema
documentation (from qemu/qapi/block-core.json), still I seem to be
tripping up somewhere.  Now it doesn't recognize the 'backing' option:

$ socat UNIX:./qmp-sock READLINE,history=$HOME/.qmp_history,prompt='QMP> '
[...]
QMP> {
QMP>   "execute":"blockdev-add",
QMP>   "arguments":{
QMP>     "driver":"qcow2",
QMP>     "node-name":"node1"
QMP>   },
QMP>   "file":{
QMP>     "driver":"file",
QMP>     "filename":"/export/target.qcow2"
QMP>   },
QMP>   "backing":{
QMP>     "driver":"qcow2",
QMP>     "file":{
QMP>       "driver":"file",
QMP>       "filename":"/export/base.qcow2"
QMP>     }
QMP>   }
QMP> }
{"error": {"class": "GenericError", "desc": "QMP input object member 'backing' is unexpected"}}
QMP> 

-- 
/kashyap