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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Anthony PERARD <anthony.perard@citrix.com>
Cc: xen-devel@lists.xenproject.org,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH v4 12/32] libxl: Design of an async API to issue QMP commands to QEMUç
Date: Fri, 3 Aug 2018 17:30:20 +0200	[thread overview]
Message-ID: <20180803153020.nt5nmeebpvksolkk@mac> (raw)
In-Reply-To: <20180803144539.GG1327@perard.uk.xensource.com>

On Fri, Aug 03, 2018 at 03:45:39PM +0100, Anthony PERARD wrote:
> On Fri, Aug 03, 2018 at 03:55:48PM +0200, Roger Pau Monné wrote:
> > On Fri, Aug 03, 2018 at 12:18:02PM +0100, Anthony PERARD wrote:
> > > On Thu, Aug 02, 2018 at 11:01:43AM +0200, Roger Pau Monné wrote:
> > > > On Fri, Jul 27, 2018 at 03:05:54PM +0100, Anthony PERARD wrote:
> > > > > +/*
> > > > > + * This facility allows a command to be sent to QEMU, and the response to be
> > > > > + * handed to a callback function.  Each libxl__ev_qmp handles zero or one
> > > > 
> > > > Do you really mean 'zero or one' or 'zero or more'?
> > > 
> > > It is zero or one. But I'm not sur that extra sentence is usefull.
> > > Initially, it was followed by "if multiple commands are to be sent
> > > concurrently, multiple libxl__ev_qmp's must be used."
> > > 
> > > But concurency between multiple libxl__ev_qmp isn't possible, the second
> > > libxl__ev_qmp created will have to wait until the first one is been
> > > disposed of. But sending multiple command can be done, by waiting for
> > > the first one to be done, then then the second one. This is why I have
> > > the paragraph about "commands can be chained".
> > 
> > Then maybe you want to add something along the lines:
> > 
> > "Multiple QMP commands can be queued in a single libxl__ev_qmp
> > instance, however they will be dispatched in a serialized fashion.
> > Note also that there can only be a single libxl__ev_qmp instance
> > active at a time."
> 
> That's not true, I don't think adding facilities to queue commands will
> be usefull, usually, one will need to wait for a response to the first
> command in order to prepare a second one. It is rare in libxl that
> several commands can be prepared and queued in advance. User of this API
> can do the queuing themself.
> 
> As for the single active instance of libxl__ev_qmp, that isn't true
> easier, several libxl__ev_qmp can be in the state "Active" at the same
> time. But only one can be in the "Connected" state at the same time (in
> relation to a single qemu) due to the way qemu handles QMP connections.

OK, I think you should remove that line (the zero or one...).
Hopefully the text in the "commands can be chained" part will already
make this clear.

Thanks, Roger.

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  reply	other threads:[~2018-08-03 15:30 UTC|newest]

Thread overview: 96+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-27 14:05 [PATCH v4 00/32] libxl: Enable save/restore/migration of a restricted QEMU + libxl__ev_qmp_* Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 01/32] libxl_event: Fix DEBUG prints Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 02/32] libxl_qmp: Documentation of the logic of the QMP client Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 03/32] libxl_qmp: Fix use of DEBUG_RECEIVED Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 04/32] libxl_json: fix build with DEBUG_ANSWER Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 05/32] libxl_qmp: Move the buffer realloc to the same scope level as read Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 06/32] libxl_qmp: Add a warning to not trust QEMU Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 07/32] libxl_qmp: Move struct sockaddr_un variable to qmp_open() Anthony PERARD
2018-08-02  8:26   ` Roger Pau Monné
2018-08-20 14:52   ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 08/32] libxl: Add libxl__prepare_sockaddr_un() helper Anthony PERARD
2018-08-02  8:36   ` Roger Pau Monné
2018-08-20 14:56   ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 09/32] libxl_qmp: Remove unused yajl_ctx from handler Anthony PERARD
2018-08-20 14:56   ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 10/32] libxl_json: constify libxl__json_object_to_yajl_gen arguments Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 11/32] libxl_dm: Add libxl__qemu_qmp_path() Anthony PERARD
2018-08-02  8:41   ` Roger Pau Monné
2018-08-20 14:57   ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 12/32] libxl: Design of an async API to issue QMP commands to QEMU Anthony PERARD
2018-08-02  9:01   ` [PATCH v4 12/32] libxl: Design of an async API to issue QMP commands to QEMUç Roger Pau Monné
2018-08-03 11:18     ` Anthony PERARD
2018-08-03 13:55       ` Roger Pau Monné
2018-08-03 14:45         ` Anthony PERARD
2018-08-03 15:30           ` Roger Pau Monné [this message]
2018-07-27 14:05 ` [PATCH v4 13/32] libxl_qmp: Connect to QMP socket Anthony PERARD
2018-08-02  9:35   ` Roger Pau Monné
2018-08-03 13:54     ` Anthony PERARD
2018-08-03 14:03       ` Roger Pau Monné
2018-08-21  8:22         ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 14/32] libxl_qmp: Implement fd callback and read data Anthony PERARD
2018-08-02  9:56   ` Roger Pau Monné
2018-08-03 14:32     ` Anthony PERARD
2018-08-03 15:24       ` Roger Pau Monné
2018-08-06 15:01         ` Anthony PERARD
2018-07-27 14:05 ` [PATCH v4 15/32] libxl_json: Enable yajl_allow_trailing_garbage Anthony PERARD
2018-08-02 10:01   ` Roger Pau Monné
2018-08-21  8:26     ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 16/32] libxl_json: libxl__json_object_to_json Anthony PERARD
2018-08-02 10:10   ` Roger Pau Monné
2018-08-21  8:26   ` Wei Liu
2018-07-27 14:05 ` [PATCH v4 17/32] libxl_qmp: Parse JSON input from QMP Anthony PERARD
2018-08-02 10:25   ` Roger Pau Monné
2018-08-03 15:33     ` Anthony PERARD
2018-08-06 11:17       ` Roger Pau Monné
2018-07-27 14:06 ` [PATCH v4 18/32] libxl_qmp: Separate QMP message generation from qmp_send_prepare Anthony PERARD
2018-08-02 10:34   ` Roger Pau Monné
2018-08-03 15:43     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 19/32] libxl_qmp: Prepare the command to be sent Anthony PERARD
2018-08-02 10:41   ` Roger Pau Monné
2018-08-03 16:35     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 20/32] libxl_qmp: Handle write to QMP socket Anthony PERARD
2018-08-02 11:02   ` Roger Pau Monné
2018-08-03 16:50     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 21/32] libxl_qmp: Simplify qmp_response_type() prototype Anthony PERARD
2018-08-02 11:03   ` Roger Pau Monné
2018-08-21  8:53   ` Wei Liu
2018-07-27 14:06 ` [PATCH v4 22/32] libxl_qmp: Handle messages from QEMU Anthony PERARD
2018-08-02 11:17   ` Roger Pau Monné
2018-08-03 17:25     ` Anthony PERARD
2018-08-06 11:25       ` Roger Pau Monné
2018-08-06 13:14         ` Anthony PERARD
2018-08-06 15:03           ` Roger Pau Monné
2018-08-21  8:58       ` Wei Liu
2018-08-21 12:50         ` Anthony PERARD
2018-08-21 14:56           ` Ian Jackson
2018-07-27 14:06 ` [PATCH v4 23/32] libxl_qmp: Respond to QMP greeting Anthony PERARD
2018-08-02 11:26   ` Roger Pau Monné
2018-08-06 17:41     ` Anthony PERARD
2018-08-21  9:00   ` Wei Liu
2018-08-21 10:51     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 24/32] libxl_qmp: Disable beautify for QMP generated cmd Anthony PERARD
2018-08-21  9:00   ` Wei Liu
2018-07-27 14:06 ` [PATCH v4 25/32] libxl_exec: Add libxl__spawn_initiate_failure Anthony PERARD
2018-08-02 11:34   ` Roger Pau Monné
2018-08-06 15:58     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 26/32] libxl_dm: Pre-open QMP socket for QEMU Anthony PERARD
2018-08-02 15:00   ` Roger Pau Monné
2018-07-27 14:06 ` [PATCH v4 27/32] libxl: QEMU startup sync based on QMP Anthony PERARD
2018-08-02 15:06   ` Roger Pau Monné
2018-07-27 14:06 ` [PATCH v4 28/32] libxl_qmp: Store advertised QEMU version in libxl__ev_qmp Anthony PERARD
2018-08-02 15:08   ` Roger Pau Monné
2018-08-06 16:52     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 29/32] libxl: Change libxl__domain_suspend_device_model() to be async Anthony PERARD
2018-08-02 15:15   ` Roger Pau Monné
2018-07-27 14:06 ` [PATCH v4 30/32] libxl: Re-implement domain_suspend_device_model using libxl__ev_qmp Anthony PERARD
2018-08-02 15:38   ` Roger Pau Monné
2018-08-06 17:07     ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 31/32] libxl_disk: Cut libxl_cdrom_insert into step Anthony PERARD
2018-08-02 15:50   ` Roger Pau Monné
2018-08-06 17:20     ` Anthony PERARD
2018-08-07 14:18       ` Roger Pau Monné
2018-08-07 14:40         ` Anthony PERARD
2018-08-21  9:08           ` Wei Liu
2018-08-21 12:58             ` Anthony PERARD
2018-07-27 14:06 ` [PATCH v4 32/32] libxl_disk: Have libxl_cdrom_insert use libxl__ev_qmp Anthony PERARD

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