Re: [Qemu-devel] [PATCH 19/22] qapi: add QMP put-event command

[Avi Kivity]

On 03/10/2011 05:41 PM, Anthony Liguori wrote:
> > I also think it should be at the protocol layer:
> >
> > > { execute: some-command, id: foo, arguments: { ... } }
> > < { result: { ... }, id: foo }
> > > { subscribe: block-io-error, id: bar, arguments: { ... } }
> > < { result: { ... } id: bar }
> > < { event: block-io-error, id: bar, data : { ... } }
> > > { unsubscribe: block-io-error, id: bar }
> > < { result: { ... } id: bar }
> >
> > So events are now protocol-level pieces like commands, and the use of 
> > tags is uniform.
>
>
> Maybe for QMPv2, but for QMPv1, this is going to introduce an 
> extremely incompatible change.

Why?  It's 100% backwards compatible.

> Actually, we missed the json-rpc boat in designing QMP.  It should 
> look like:

IIRC I looked at it and it didn't impress me.

> > { method: some-command, id: foo, params: { ... } }
> < { result: { ... }, id: foo, params: { ... }, error: null }
> > { method: connect-block-io-error, id: bar, params: { ... } }
> < { result: { ... }, id: bar, error: null }
> < { method: block-io-error, id: null, params: { ... } }



> Keys are different and null is passed instead of not including a tag.  
> Events are sent exactly like methods but id is null.  A result is 
> never sent to the server for an event.

That means that we need a per-event command, instead of making it 
protocol-level.

> One of the good things about using a code generator and IDL though is 
> that we can add a -qmp dev,protocol=json-rpc that encodes 
> appropriately.  We can probably do this translation at the QObject 
> level really.  But in the future, we can also add -qmp 
> dev,protocol=xml-rpc, -qmp dev,protocol=rest, or -qmp 
> dev,protocol=asn1-rpc

Let's get one protocol that works first.

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