Re: [Qemu-block] [Qemu-devel] [PATCH v3 1/5] support nbd driver in blockdev-add

[Wen Congyang]

On 09/15/2015 09:11 PM, Eric Blake wrote:
> On 09/14/2015 09:58 PM, Wen Congyang wrote:
>> On 09/15/2015 11:46 AM, Eric Blake wrote:
>>> On 09/14/2015 08:27 PM, Wen Congyang wrote:
>>>>> Building fails:
>>>>>   GEN   qmp-commands.h
>>>>> In file included from /work/src/qemu/qapi-schema.json:9:
>>>>> In file included from /work/src/qemu/qapi/block.json:6:
>>>>> /work/src/qemu/qapi/block-core.json:1844: Flat union 'BlockdevOptionsNBD' 
>>>>> must have a string base field
>>>>> Makefile:286: recipe for target 'qmp-commands.h' failed
>>>>> make: *** [qmp-commands.h] Error 1
>>>
>>> Yep, doesn't work until pending qapi patches land.
>>
>> This patchset: qapi: QMP introspection?
> 
> That, and "qapi-ify netdev_add, and other post-introspection cleanups"
> https://lists.gnu.org/archive/html/qemu-devel/2015-09/msg02580.html
> 
> and "qapi: support anonymous inline base"
> https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg02346.html
> [still needs rebasing to latest versions of the other series]
> 
> 
>>>
>>> Possible workaround in the meantime - instead of trying to go with a
>>> nice flat union (where all QMP keys are in the same {} level), we can
>>> use nesting (structs that add another {} to include the unions).
>>
>> How to include the unions to a structs? Use 'base'?
> 
> Conceptually, by adding a layer of nesting.  On the wire, instead of:
> 
> { "switch1":"value", "switch2":"value", "body2":"blah" }
> 
> you would instead have:
> 
> { "switch1":"value", "data": { "switch2":"value", "body2":"blah" } }
> 
> Anywhere in qapi that you try to have:
> { 'union': ..., 'data':{'switch1':'Union'}}
> 
> you instead create a wrapper type:
> { 'struct':'Wrapper', 'data':{'data':'Union'}}
> { 'union': ..., 'data':{'switch1':'Wrapper'}}

If so, the option is "data.switch1" not "switch1"

> 
> 
> What I don't know is whether the extra QMP nesting makes it easier or
> harder to support the existing NBD command line options, and it would

Yes, it is harder to support it.

Thanks
Wen Congyang

> ultimately be nice to have unified support so that anything we can do on
> the command line can be expressed in QMP; and anything we can do in QMP
> can be expressed on the command line without undue nesting.
>