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Date: Thu, 10 Mar 2011 10:42:01 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 19/22] qapi: add QMP put-event command
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To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>

On 03/10/2011 09:49 AM, Avi Kivity wrote:
> 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.

It's a very significant change for clients.  While technical compatible, 
it would require a change to the client infrastructure to support the 
new feature.

I'm not saying we shouldn't make a change like this, but we should 
minimize these type of changes.

Regards,

Anthony Liguori