Re: [Qemu-devel] [RFC 00/15] QMP: out-of-band (OOB) execution support

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> This series was born from this one:
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg04310.html

Are patches 1..6 separable and mergable without the rest ?

Dave

> The design comes from Markus, and also the whole-bunch-of discussions
> in previous thread.  My heartful thanks to Markus, Daniel, Dave,
> Stefan, etc. on discussing the topic (...again!), providing shiny
> ideas and suggestions.  Finally we got such a solution that seems to
> satisfy everyone.
> 
> I re-started the versioning since this series is totally different
> from previous one.  Now it's version 1.
> 
> In case new reviewers come along the way without reading previous
> discussions, I will try to do a summary on what this is all about.
> 
> What is OOB execution?
> ======================
> 
> It's the shortcut of Out-Of-Band execution, its name is given by
> Markus.  It's a way to quickly execute a QMP request.  Say, originally
> QMP is going throw these steps:
> 
>       JSON Parser --> QMP Dispatcher --> Respond
>           /|\    (2)                (3)     |
>        (1) |                               \|/ (4)
>            +---------  main thread  --------+
> 
> The requests are executed by the so-called QMP-dispatcher after the
> JSON is parsed.  If OOB is on, we run the command directly in the
> parser and quickly returns.
> 
> Yeah I know in current code the parser calls dispatcher directly
> (please see handle_qmp_command()).  However it's not true again after
> this series (parser will has its own IO thread, and dispatcher will
> still be run in main thread).  So this OOB does brings something
> different.
> 
> There are more details on why OOB and the difference/relationship
> between OOB, async QMP, block/general jobs, etc.. but IMHO that's
> slightly out of topic (and believe me, it's not easy for me to
> summarize that).  For more information, please refers to [1].
> 
> Summary ends here.
> 
> Some Implementation Details
> ===========================
> 
> Again, I mentioned that the old QMP workflow is this:
> 
>       JSON Parser --> QMP Dispatcher --> Respond
>           /|\    (2)                (3)     |
>        (1) |                               \|/ (4)
>            +---------  main thread  --------+
> 
> What this series does is, firstly:
> 
>       JSON Parser     QMP Dispatcher --> Respond
>           /|\ |           /|\       (4)     |
>            |  | (2)        | (3)            |  (5)
>        (1) |  +----->      |               \|/
>            +---------  main thread  <-------+
> 
> And further:
> 
>                queue/kick
>      JSON Parser ======> QMP Dispatcher --> Respond
>          /|\ |     (3)       /|\        (4)    |
>       (1) |  | (2)            |                |  (5)
>           | \|/               |               \|/
>         IO thread         main thread  <-------+
> 
> Then it introduced the "allow-oob" parameter in QAPI schema to define
> commands, and "run-oob" flag to let oob-allowed command to run in the
> parser.
> 
> The last patch enables this for "migrate-incoming" command.
> 
> Please review.  Thanks.
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg04310.html
> 
> Peter Xu (15):
>   char-io: fix possible race on IOWatchPoll
>   qobject: allow NULL for qstring_get_str()
>   qobject: introduce qobject_to_str()
>   monitor: move skip_flush into monitor_data_init
>   qjson: add "opaque" field to JSONMessageParser
>   monitor: move the cur_mon hack deeper for QMP
>   monitor: unify global init
>   monitor: create IO thread
>   monitor: allow to use IO thread for parsing
>   monitor: introduce monitor_qmp_respond()
>   monitor: separate QMP parser and dispatcher
>   monitor: enable IO thread for (qmp & !mux) typed
>   qapi: introduce new cmd option "allow-oob"
>   qmp: support out-of-band (oob) execution
>   qmp: let migrate-incoming allow out-of-band
> 
>  chardev/char-io.c                |  15 ++-
>  docs/devel/qapi-code-gen.txt     |  51 ++++++-
>  include/monitor/monitor.h        |   2 +-
>  include/qapi/qmp/dispatch.h      |   2 +
>  include/qapi/qmp/json-streamer.h |   8 +-
>  include/qapi/qmp/qstring.h       |   1 +
>  monitor.c                        | 283 +++++++++++++++++++++++++++++++--------
>  qapi/introspect.json             |   6 +-
>  qapi/migration.json              |   3 +-
>  qapi/qmp-dispatch.c              |  34 +++++
>  qga/main.c                       |   5 +-
>  qobject/json-streamer.c          |   7 +-
>  qobject/qjson.c                  |   5 +-
>  qobject/qstring.c                |  13 +-
>  scripts/qapi-commands.py         |  19 ++-
>  scripts/qapi-introspect.py       |  10 +-
>  scripts/qapi.py                  |  15 ++-
>  scripts/qapi2texi.py             |   2 +-
>  tests/libqtest.c                 |   5 +-
>  tests/qapi-schema/test-qapi.py   |   2 +-
>  trace-events                     |   2 +
>  vl.c                             |   3 +-
>  22 files changed, 398 insertions(+), 95 deletions(-)
> 
> -- 
> 2.7.4
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK