From: "Marc-André Lureau" <marcandre.lureau@gmail.com>
To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: QEMU <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] RFC: async commands with QMP
Date: Wed, 29 Jul 2015 17:18:10 +0200 [thread overview]
Message-ID: <CAJ+F1CLueL9JcXo3eqhVUUi6nWG4Y3+La=s8v3v99uHHCcn8-g@mail.gmail.com> (raw)
In-Reply-To: <20150729150531.GI16847@redhat.com>
Hi Daniel
On Wed, Jul 29, 2015 at 5:05 PM, Daniel P. Berrange <berrange@redhat.com> wrote:
> 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. 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.
Thanks for the historic reasons, I ignored that.
Querying status is not incompatible with having async commands. It's
not because command return immediately that the job is finished, it's
async already! This proposal is about having a return when the job is
actually finished to avoid having to continuously query, that's the
main motivation. Today's return for async commands is pretty useless,
you can admit, it's just a ack that the command got accepted and
eventually started...
Also commands can be tight to the lifecycle of a client. Take memsave
or screendump, if you give them a client fd, you actually don't care
if the client is gone: there is no need to query about the status of
those commands. Instead, they should be cancelled when the client is
gone.
--
Marc-André Lureau
next prev parent reply other threads:[~2015-07-29 15:18 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
2015-07-29 15:32 ` Marc-André Lureau
2015-07-29 15:45 ` Daniel P. Berrange
2015-07-29 15:18 ` Marc-André Lureau [this message]
2015-09-14 13:45 ` Markus Armbruster
2015-09-14 16:01 ` Marc-André Lureau
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