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Re: [Qemu-devel] Adding an overlay with 'blockdev-add' fails with: "Para
From: |
Kashyap Chamarthy |
Subject: |
Re: [Qemu-devel] Adding an overlay with 'blockdev-add' fails with: "Parameter 'driver' is missing" |
Date: |
Fri, 24 Feb 2017 11:53:12 +0100 |
User-agent: |
Mutt/1.6.0.1 (2016-04-01) |
On Thu, Feb 23, 2017 at 10:51:38AM -0600, Eric Blake wrote:
> On 02/23/2017 10:33 AM, Kashyap Chamarthy wrote:
[...]
> > 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> },
>
> Oops, you ended your arguments too soon.
Sigh, that was a stray closing bracket that I didn't clean up (it was
part of the "cache" section that I borrowed from the schema docs).
> > QMP> "file":{
> > QMP> "driver":"file",
> > QMP> "filename":"/export/target.qcow2"
> > QMP> },
> > QMP> "backing":{
>
> Here, you passed "file" and "backing" as siblings of "execute", but they
> should be children of "arguments".
Oops, you're right.
[...]
> Try (untested on my end) this rewrite of your original post (just
> removing the '"options":{' and corresponding '}' from that listing):
>
> {
> "execute": "blockdev-add",
> "arguments": {
> "backing": "virtio0",
> "driver": "qcow2",
> "id": "virtio1",
> "file": {
> "driver": "file",
> "filename": "/export/target.qcow2"
> }
> }
> }
This does not work (tested), because my current QEMU build from Git,
will reject the "id" key (Kevin mentioned so on IRC, but I couldn't
find the relevant Git commit from my `grep`ing in the Git history):
{"error": {"class": "GenericError", "desc": "QMP input object member 'id' is
unexpected"}}
> or this attempt at your current post:
>
> { "execute":"blockdev-add",
> "arguments":{
> "driver":"qcow2",
> "node-name":"node1"
A comma missing here :-) With that fixed, it returns success.
However, bizzarely enough, when I ran `query-block` after `blockdev-add`
succeeded (well, at least after it returned success), I don't see the
new node ('target.qcow2') reflected in the return output. Me
investigates.
https://kashyapc.fedorapeople.org/virt/temp/blockdev-add-followed-by-buggy-query-block.txt
> "file":{
> "driver":"file",
> "filename":"/export/target.qcow2"
> },
> "backing":{
> "driver":"qcow2",
> "file":{
> "driver":"file",
> "filename":"/export/base.qcow2"
> }
> }
> }
> }
Just for completeness, the new working incantation (that removes the
need for "options" indirection, and the "id" key) that takes
'node-name':
--------------------------------------------
{
"execute":"blockdev-add",
"arguments":{
"driver":"qcow2",
"node-name":"node1",
"file":{
"driver":"file",
"filename":"/export/target.qcow2"
},
"backing":{
"driver":"qcow2",
"file":{
"driver":"file",
"filename":"/export/base.qcow2"
}
}
}
}
--------------------------------------------
--
/kashyap