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.

v8:
- Replaced bdrv_co_move_to_aio_context() with bdrv_co_enter()/leave(),
  added bdrv_co_lock()/unlock() and fixed the iothread support in
  qmp_block_resize() with the new functions [Stefan]
- More detailed documentation of 'coroutine' flag for commands [Markus]
- Improved comment for dropping out of coroutine context in
  qmp_dispatch() [Markus]
- Coding style changes [Markus]
- Resolve some more merge conflicts on rebase

v7:
- Added patch 2 to add a Monitor parameter to monitor_get_cpu_index(),
  too [Markus]
- Let monitor_set_cur() return the old monitor [Markus]
- Fixed comment about linking stub objects in test-util-sockets [Markus]
- More detailed commit message for per-coroutine current monitor and
  document that monitor_set_cur(NULL) must be called eventually [Markus]
- Resolve some merge conflicts on rebase

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 (14):
  monitor: Add Monitor parameter to monitor_set_cpu()
  monitor: Add Monitor parameter to monitor_get_cpu_index()
  monitor: Use getter/setter functions for cur_mon
  hmp: Update current monitor 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_enter()/leave()
  block: Add bdrv_lock()/unlock()
  block: Convert 'block_resize' to coroutine

 qapi/block-core.json                    |   3 +-
 docs/devel/qapi-code-gen.txt            |  29 ++++++
 docs/sphinx/qapidoc.py                  |   2 +-
 include/block/aio.h                     |  10 ++
 include/block/block.h                   |  31 ++++++
 include/monitor/monitor.h               |   7 +-
 include/qapi/qmp/dispatch.h             |   5 +-
 monitor/monitor-internal.h              |   7 +-
 audio/wavcapture.c                      |   8 +-
 block.c                                 |  50 +++++++++
 blockdev.c                              |  16 +--
 dump/dump.c                             |   2 +-
 hw/core/machine-hmp-cmds.c              |   2 +-
 hw/scsi/vhost-scsi.c                    |   2 +-
 hw/virtio/vhost-vsock.c                 |   2 +-
 migration/fd.c                          |   4 +-
 monitor/hmp-cmds.c                      |   4 +-
 monitor/hmp.c                           |  44 ++++++--
 monitor/misc.c                          |  38 +++----
 monitor/monitor.c                       | 101 ++++++++++++++++--
 monitor/qmp-cmds-control.c              |   2 +
 monitor/qmp-cmds.c                      |   2 +-
 monitor/qmp.c                           | 131 +++++++++++++++++-------
 net/socket.c                            |   2 +-
 net/tap.c                               |   6 +-
 qapi/qmp-dispatch.c                     |  65 +++++++++++-
 qapi/qmp-registry.c                     |   3 +
 qga/main.c                              |   2 +-
 softmmu/cpus.c                          |   2 +-
 stubs/monitor-core.c                    |  10 +-
 tests/test-qmp-cmds.c                   |  10 +-
 tests/test-util-sockets.c               |  12 +--
 trace/control.c                         |   2 +-
 util/aio-posix.c                        |   8 +-
 util/async.c                            |  30 ++++++
 util/qemu-error.c                       |   6 +-
 util/qemu-print.c                       |   3 +-
 util/qemu-sockets.c                     |   1 +
 scripts/qapi/commands.py                |  10 +-
 scripts/qapi/expr.py                    |  11 +-
 scripts/qapi/introspect.py              |   2 +-
 scripts/qapi/schema.py                  |  13 ++-
 tests/qapi-schema/test-qapi.py          |   7 +-
 hmp-commands.hx                         |   1 +
 tests/qapi-schema/meson.build           |   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 +
 50 files changed, 573 insertions(+), 143 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

-- 
2.25.4

Kevin Wolf <kwolf@redhat.com> writes:

> 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.

PATCH 01-10:
Reviewed-by: Markus Armbruster <armbru@redhat.com>

PATCH 11-14 are for Stefan to review.

I can take this through my tree once that's done.

Marc-André, I figure rebasing your "[PATCH] console: make QMP screendump
use coroutine" on top of this is now low risk.  No rush, of course.

On Mon, Oct 05, 2020 at 05:58:41PM +0200, Kevin Wolf wrote:
> 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.
> 
> v8:
> - Replaced bdrv_co_move_to_aio_context() with bdrv_co_enter()/leave(),
>   added bdrv_co_lock()/unlock() and fixed the iothread support in
>   qmp_block_resize() with the new functions [Stefan]
> - More detailed documentation of 'coroutine' flag for commands [Markus]
> - Improved comment for dropping out of coroutine context in
>   qmp_dispatch() [Markus]
> - Coding style changes [Markus]
> - Resolve some more merge conflicts on rebase
> 
> v7:
> - Added patch 2 to add a Monitor parameter to monitor_get_cpu_index(),
>   too [Markus]
> - Let monitor_set_cur() return the old monitor [Markus]
> - Fixed comment about linking stub objects in test-util-sockets [Markus]
> - More detailed commit message for per-coroutine current monitor and
>   document that monitor_set_cur(NULL) must be called eventually [Markus]
> - Resolve some merge conflicts on rebase
> 
> 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 (14):
>   monitor: Add Monitor parameter to monitor_set_cpu()
>   monitor: Add Monitor parameter to monitor_get_cpu_index()
>   monitor: Use getter/setter functions for cur_mon
>   hmp: Update current monitor 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_enter()/leave()
>   block: Add bdrv_lock()/unlock()
>   block: Convert 'block_resize' to coroutine
> 
>  qapi/block-core.json                    |   3 +-
>  docs/devel/qapi-code-gen.txt            |  29 ++++++
>  docs/sphinx/qapidoc.py                  |   2 +-
>  include/block/aio.h                     |  10 ++
>  include/block/block.h                   |  31 ++++++
>  include/monitor/monitor.h               |   7 +-
>  include/qapi/qmp/dispatch.h             |   5 +-
>  monitor/monitor-internal.h              |   7 +-
>  audio/wavcapture.c                      |   8 +-
>  block.c                                 |  50 +++++++++
>  blockdev.c                              |  16 +--
>  dump/dump.c                             |   2 +-
>  hw/core/machine-hmp-cmds.c              |   2 +-
>  hw/scsi/vhost-scsi.c                    |   2 +-
>  hw/virtio/vhost-vsock.c                 |   2 +-
>  migration/fd.c                          |   4 +-
>  monitor/hmp-cmds.c                      |   4 +-
>  monitor/hmp.c                           |  44 ++++++--
>  monitor/misc.c                          |  38 +++----
>  monitor/monitor.c                       | 101 ++++++++++++++++--
>  monitor/qmp-cmds-control.c              |   2 +
>  monitor/qmp-cmds.c                      |   2 +-
>  monitor/qmp.c                           | 131 +++++++++++++++++-------
>  net/socket.c                            |   2 +-
>  net/tap.c                               |   6 +-
>  qapi/qmp-dispatch.c                     |  65 +++++++++++-
>  qapi/qmp-registry.c                     |   3 +
>  qga/main.c                              |   2 +-
>  softmmu/cpus.c                          |   2 +-
>  stubs/monitor-core.c                    |  10 +-
>  tests/test-qmp-cmds.c                   |  10 +-
>  tests/test-util-sockets.c               |  12 +--
>  trace/control.c                         |   2 +-
>  util/aio-posix.c                        |   8 +-
>  util/async.c                            |  30 ++++++
>  util/qemu-error.c                       |   6 +-
>  util/qemu-print.c                       |   3 +-
>  util/qemu-sockets.c                     |   1 +
>  scripts/qapi/commands.py                |  10 +-
>  scripts/qapi/expr.py                    |  11 +-
>  scripts/qapi/introspect.py              |   2 +-
>  scripts/qapi/schema.py                  |  13 ++-
>  tests/qapi-schema/test-qapi.py          |   7 +-
>  hmp-commands.hx                         |   1 +
>  tests/qapi-schema/meson.build           |   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 +
>  50 files changed, 573 insertions(+), 143 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
> 
> -- 
> 2.25.4
> 

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>