From: Eric Blake <eblake@redhat.com>
To: "Daniel P. Berrange" <berrange@redhat.com>,
"Marc-André Lureau" <marcandre.lureau@gmail.com>
Cc: QEMU <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] RFC: async commands with QMP
Date: Wed, 29 Jul 2015 09:10:54 -0600 [thread overview]
Message-ID: <55B8ECFE.6000707@redhat.com> (raw)
In-Reply-To: <20150729150531.GI16847@redhat.com>
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On 07/29/2015 09:05 AM, Daniel P. Berrange wrote:
>> In order to make "async" variant possible, "id" would have to be
>> provided and unique. I think the async support should also be
>> announced in the qmp_capabilities. Commands would have to opt-in for
>> async support in the schema. An async return wouldn't be allowed when
>> a blocking command is ongoing.
>>
>> There are many variations possible on the same idea. We could
>> introduce new _async functions instead, and keep the "id"
>> requirements. Or alternatively, an "async_id" could be generated by
>> qemu and returned immediately. Then the reply of the command could be
>> an event instead. Ex:
>>
>
> When QMP was originally written there was some infrastructure for doing
> async commands, but over time this has all been ripped out because it
> was never really used, complicated the code and didn't work too well
> either. It seems we pretty much settled on the approach that all
> commands should be fast to execute, and where there is a long term
> job being run, we have commands to query its status, cancel it, and
> sometimes events too.
In fact, see commit 65207c59, where we ripped it out with prejudice.
> One of the benefits of this is that it means
> that libvirt can determine current status of ongoing background jobs
> when it restarts and reconnects to a previously launched QEMU, where
> as an async command approach is tied to the specific monitor connection
> that is open.
And that is a real concern with any new proposal for async commands.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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next prev parent reply other threads:[~2015-07-29 15:11 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-29 14:49 [Qemu-devel] RFC: async commands with QMP Marc-André Lureau
2015-07-29 14:51 ` Marc-André Lureau
2015-07-29 15:05 ` Daniel P. Berrange
2015-07-29 15:10 ` Eric Blake [this message]
2015-07-29 15:32 ` Marc-André Lureau
2015-07-29 15:45 ` Daniel P. Berrange
2015-07-29 15:18 ` Marc-André Lureau
2015-09-14 13:45 ` Markus Armbruster
2015-09-14 16:01 ` Marc-André Lureau
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