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

[Avi Kivity]

On 03/10/2011 04:24 PM, Avi Kivity wrote:
> > > What would the wire exchange look like?
> >
> > > { 'execute': 'get-block-io-error-event' }
> > < { 'return' : 32 }
> > ...
> > < { 'event': 'BLOCK_IO_ERROR', 'data': { 'action': 'stop', 'device': 
> > 'ide0-hd0', 'operation': 'read' }, 'tag': 32 }
> > ...
> > > { 'execute': 'put-event', 'arguments': { 'tag': 32 } }
>
>
> Well, I may be biased, but I prefer my variant.
>
> btw, it's good to decree that a subscription is immediately followed 
> by an event with the current state (which means events have to provide 
> state and be idempotent); so the subscribe-and-query pattern is 
> provided automatically.
>
> btw2, I now nominate subscribe and unsubscribe as replacements for get 
> and put.

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.

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