[v5,0/4] qmp: Optionally run handlers in coroutines

Message

Kevin Wolf Feb. 18, 2020, 3:40 p.m. UTC

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.

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 (4):
  qapi: Add a 'coroutine' flag for commands
  vl: Initialise main loop earlier
  qmp: Move dispatcher to a coroutine
  block: Mark 'block_resize' as coroutine

 qapi/block-core.json                    |   3 +-
 docs/devel/qapi-code-gen.txt            |  11 +++
 include/qapi/qmp/dispatch.h             |   2 +
 monitor/monitor-internal.h              |   6 +-
 monitor/monitor.c                       |  55 +++++++++--
 monitor/qmp.c                           | 122 ++++++++++++++++++------
 qapi/qmp-dispatch.c                     |  44 ++++++++-
 qapi/qmp-registry.c                     |   3 +
 tests/test-qmp-cmds.c                   |   4 +
 util/aio-posix.c                        |   7 +-
 vl.c                                    |  10 +-
 scripts/qapi/commands.py                |  10 +-
 scripts/qapi/doc.py                     |   2 +-
 scripts/qapi/expr.py                    |  10 +-
 scripts/qapi/introspect.py              |   2 +-
 scripts/qapi/schema.py                  |   9 +-
 tests/qapi-schema/test-qapi.py          |   7 +-
 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 +
 23 files changed, 254 insertions(+), 61 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

Comments

Markus Armbruster March 3, 2020, 3:33 p.m. UTC | #1

Looks like PATCH 2 isn't necessary anymore, and PATCH 4 needs a respin.
I tentatively queued PATCH 1+3, in the hope of getting either PATCH 4 or
Marc-André's screendump patch in time for 5.0.

Pushed to branch monitor-next in git://repo.or.cz/qemu/armbru.git.
Appears to be down right now.

Thanks!