[v6,00/12] monitor: Optionally run handlers in coroutines

Some QMP command handlers can block the main loop for a relatively long
time, for example because they perform some I/O. This is quite nasty.
Allowing such handlers to run in a coroutine where they can yield (and
therefore release the BQL) while waiting for an event such as I/O
completion solves the problem.

This series adds the infrastructure to allow this and switches
block_resize to run in a coroutine as a first example.

This is an alternative solution to Marc-André's "monitor: add
asynchronous command type" series.

v6:
- Fixed cur_mon behaviour: It should always point to the Monitor while
  we're in the handler coroutine, but be NULL while the handler
  coroutines has yielded. [Markus]
- Give HMP handlers the coroutine option, too, because they will call
  QMP handlers, and life is easier when we know whether we are in
  coroutine context or not.
- Fixed block_resize for block devices in iothreads and for HMP
- Resolved some merge conflict with QAPI generator and monitor
  refactorings that were merged in the meantime

v5:
- Improved comments and documentation [Markus]

v4:
- Forbid 'oob': true, 'coroutine': true [Markus]
- Removed Python type hints [Markus]
- Introduced separate bool qmp_dispatcher_co_shutdown to make it clearer
  how a shutdown request is signalled to the dispatcher [Markus]
- Allow using aio_poll() with iohandler_ctx and use that instead of
  aio_bh_poll() [Markus]
- Removed coroutine_fn from qmp_block_resize() again because at least
  one caller (HMP) calls it outside of coroutine context [Markus]
- Tried to make the synchronisation between dispatcher and the monitor
  thread clearer, and fixed a race condition
- Improved documentation and comments

v3:
- Fix race between monitor thread and dispatcher that could schedule the
  dispatcher coroutine twice if a second requests comes in before the
  dispatcher can wake up [Patchew]

v2:
- Fix typo in a commit message [Eric]
- Use hyphen instead of underscore for the test command [Eric]
- Mark qmp_block_resize() as coroutine_fn [Stefan]


Kevin Wolf (12):
  monitor: Add Monitor parameter to monitor_set_cpu()
  monitor: Use getter/setter functions for cur_mon
  hmp: Set cur_mon only in handle_hmp_command()
  qmp: Assert that no other monitor is active
  qmp: Call monitor_set_cur() only in qmp_dispatch()
  monitor: Make current monitor a per-coroutine property
  qapi: Add a 'coroutine' flag for commands
  qmp: Move dispatcher to a coroutine
  hmp: Add support for coroutine command handlers
  util/async: Add aio_co_reschedule_self()
  block: Add bdrv_co_move_to_aio_context()
  block: Convert 'block_resize' to coroutine

 qapi/block-core.json                    |   3 +-
 docs/devel/qapi-code-gen.txt            |  12 +++
 include/block/aio.h                     |  10 ++
 include/block/block.h                   |   6 ++
 include/monitor/monitor.h               |   5 +-
 include/qapi/qmp/dispatch.h             |   5 +-
 monitor/monitor-internal.h              |   7 +-
 audio/wavcapture.c                      |   8 +-
 block.c                                 |  10 ++
 blockdev.c                              |  13 ++-
 dump/dump.c                             |   2 +-
 hw/scsi/vhost-scsi.c                    |   2 +-
 hw/virtio/vhost-vsock.c                 |   2 +-
 migration/fd.c                          |   4 +-
 monitor/hmp-cmds.c                      |   2 +-
 monitor/hmp.c                           |  51 +++++++---
 monitor/misc.c                          |  21 ++--
 monitor/monitor.c                       |  87 ++++++++++++++--
 monitor/qmp-cmds-control.c              |   2 +
 monitor/qmp-cmds.c                      |   2 +-
 monitor/qmp.c                           | 130 +++++++++++++++++-------
 net/socket.c                            |   2 +-
 net/tap.c                               |   6 +-
 qapi/qmp-dispatch.c                     |  52 +++++++++-
 qapi/qmp-registry.c                     |   3 +
 qga/main.c                              |   2 +-
 stubs/monitor-core.c                    |   9 +-
 tests/test-qmp-cmds.c                   |  10 +-
 tests/test-util-sockets.c               |  22 ++--
 trace/control.c                         |   2 +-
 util/aio-posix.c                        |   8 +-
 util/async.c                            |  30 ++++++
 util/qemu-error.c                       |   4 +-
 util/qemu-print.c                       |   3 +-
 util/qemu-sockets.c                     |   1 +
 scripts/qapi/commands.py                |  10 +-
 scripts/qapi/doc.py                     |   2 +-
 scripts/qapi/expr.py                    |  10 +-
 scripts/qapi/introspect.py              |   2 +-
 scripts/qapi/schema.py                  |  12 ++-
 tests/qapi-schema/test-qapi.py          |   7 +-
 hmp-commands.hx                         |   1 +
 tests/Makefile.include                  |   1 +
 tests/qapi-schema/oob-coroutine.err     |   2 +
 tests/qapi-schema/oob-coroutine.json    |   2 +
 tests/qapi-schema/oob-coroutine.out     |   0
 tests/qapi-schema/qapi-schema-test.json |   1 +
 tests/qapi-schema/qapi-schema-test.out  |   2 +
 48 files changed, 454 insertions(+), 136 deletions(-)
 create mode 100644 tests/qapi-schema/oob-coroutine.err
 create mode 100644 tests/qapi-schema/oob-coroutine.json
 create mode 100644 tests/qapi-schema/oob-coroutine.out

Markus Armbruster <armbru@redhat.com> writes:

> Markus Armbruster <armbru@redhat.com> writes:
>
>> I let this series slide to get my Error API rework done, along with much
>> else.  My sincere apologies!
>>
>> Unsurprisingly, it needs a rebase now.  I suggest to let me review it as
>> is first.
>
> I'm done with v6.  Summary:
>
> * A few trivial things to correct here and there.
>
> * A few ideas to improve things in relatively minor ways.
>
> * PATCH 03 looks "why bother" to me until PATCH 09 makes me suspect you
>   did the former to enable the latter.  If you had captured that in your
>   commit message back then, like you did for the similar PATCH 05, I
>   wouldn't be scratching my head now :)
>
> * I dislike PATCH 06, and would like to explore an alternative idea.
>
> * PATCH 08 makes hairy monitor code even hairier, but I don't have
>   better ideas.
>
> * I don't feel comfortable as a sole reviewer of the AIO magic in PATCH
>   10-12.  Let's ask Stefan for an eye-over.
>
> I'd like to proceed as follows.  You rebase, and address "easy" review
> comments (you decide what's easy).  Post as v7, cc'ing Stefan for the
> AIO magic and David Gilbert for HMP.  While they review (hopefully), I
> explore a replacement for PATCH 06.  And then we touch bases and decide
> how to get this thing wrapped.

I explored:

    Subject: Ways to do per-coroutine properties (was: [PATCH v6 06/12] monitor: Make current monitor a per-coroutine property)
    Date: Fri, 07 Aug 2020 15:09:19 +0200 (3 weeks, 5 days, 21 hours ago)
    Message-ID: <87a6z6wqkg.fsf_-_@dusky.pond.sub.org>

May I have v7?  Feel free to keep your PATCH 06.  If I decide to replace
it, I can do it myself, possibly on top.

Am 03.09.2020 um 12:49 hat Markus Armbruster geschrieben:
> Markus Armbruster <armbru@redhat.com> writes:
> 
> > Markus Armbruster <armbru@redhat.com> writes:
> >
> >> I let this series slide to get my Error API rework done, along with much
> >> else.  My sincere apologies!
> >>
> >> Unsurprisingly, it needs a rebase now.  I suggest to let me review it as
> >> is first.
> >
> > I'm done with v6.  Summary:
> >
> > * A few trivial things to correct here and there.
> >
> > * A few ideas to improve things in relatively minor ways.
> >
> > * PATCH 03 looks "why bother" to me until PATCH 09 makes me suspect you
> >   did the former to enable the latter.  If you had captured that in your
> >   commit message back then, like you did for the similar PATCH 05, I
> >   wouldn't be scratching my head now :)
> >
> > * I dislike PATCH 06, and would like to explore an alternative idea.
> >
> > * PATCH 08 makes hairy monitor code even hairier, but I don't have
> >   better ideas.
> >
> > * I don't feel comfortable as a sole reviewer of the AIO magic in PATCH
> >   10-12.  Let's ask Stefan for an eye-over.
> >
> > I'd like to proceed as follows.  You rebase, and address "easy" review
> > comments (you decide what's easy).  Post as v7, cc'ing Stefan for the
> > AIO magic and David Gilbert for HMP.  While they review (hopefully), I
> > explore a replacement for PATCH 06.  And then we touch bases and decide
> > how to get this thing wrapped.
> 
> I explored:
> 
>     Subject: Ways to do per-coroutine properties (was: [PATCH v6 06/12] monitor: Make current monitor a per-coroutine property)
>     Date: Fri, 07 Aug 2020 15:09:19 +0200 (3 weeks, 5 days, 21 hours ago)
>     Message-ID: <87a6z6wqkg.fsf_-_@dusky.pond.sub.org>
> 
> May I have v7?  Feel free to keep your PATCH 06.  If I decide to replace
> it, I can do it myself, possibly on top.

It's one of the next things on my list. I can't promise anything more
specific, though.

Kevin