[Qemu-devel] [PATCH v2 00/17] aio: drop io_flush()

[Stefan Hajnoczi]

This series gets rid of aio's .io_flush() callback.  It's based on Paolo's
insight that bdrv_drain_all() can be implemented using the bs->tracked_requests
list.  io_flush() is redundant since the block layer already knows if requests
are pending.

The point of this effort is to simplify our event loop(s).  If we can reduce
custom features like io_flush() it becomes easier to unify event loops and
reuse glib or other options.

This is also important to me for dataplane, since bdrv_drain_all() is one of
the synchronization points between threads.  QEMU monitor commands invoke
bdrv_drain_all() while the block device is accessed from a dataplane thread.

Background on io_flush() semantics:

The io_flush() handler must return 1 if this aio fd handler is active.  That
is, requests are pending and we'd like to make progress by monitoring the fd.

If io_flush() returns 0, the aio event loop skips monitoring this fd.  This is
critical for block drivers like iscsi where we have an idle TCP socket which we
want to block on *only* when there are pending requests.

The series works as follows:

Part 1 - stop relying on .io_flush()

The first patches change aio_poll() callers to check their termination
condition themselves instead of relying on .io_flush():

  1 block: stop relying on io_flush() in bdrv_drain_all()
  2 dataplane/virtio-blk: check exit conditions before aio_poll()
  3 tests: adjust test-aio to new aio_poll() semantics
  4 tests: adjust test-thread-pool to new aio_poll() semantics

Part 2 - stop calling .io_flush() from aio_poll()

The semantic change to aio_poll() is made here:

  5 aio: stop using .io_flush()

Part 3 - drop io_flush() handlers, just pass NULL for the io_flush argument

Remove the now dead code from all .io_flush() users:

  6 block/curl: drop curl_aio_flush()
  7 block/gluster: drop qemu_gluster_aio_flush_cb()
  8 block/iscsi: drop iscsi_process_flush()
  9 block/linux-aio: drop qemu_laio_completion_cb()
 10 block/nbd: drop nbd_have_request()
 11 block/rbd: drop qemu_rbd_aio_flush_cb()
 12 block/sheepdog: drop have_co_req() and aio_flush_request()
 13 block/ssh: drop return_true()
 14 dataplane/virtio-blk: drop flush_true() and flush_io()
 15 thread-pool: drop thread_pool_active()

Part 4 - remove io_flush arguments from aio functions

The big, mechanical patch that drops the io_flush argument:

 16 tests: drop event_active_cb()

Note that I split Part 3 from Part 4 so it's easy to review individual block
drivers.

Stefan Hajnoczi (17):
  block: stop relying on io_flush() in bdrv_drain_all()
  dataplane/virtio-blk: check exit conditions before aio_poll()
  tests: adjust test-aio to new aio_poll() semantics
  tests: adjust test-thread-pool to new aio_poll() semantics
  aio: stop using .io_flush()
  block/curl: drop curl_aio_flush()
  block/gluster: drop qemu_gluster_aio_flush_cb()
  block/iscsi: drop iscsi_process_flush()
  block/linux-aio: drop qemu_laio_completion_cb()
  block/nbd: drop nbd_have_request()
  block/rbd: drop qemu_rbd_aio_flush_cb()
  block/sheepdog: drop have_co_req() and aio_flush_request()
  block/ssh: drop return_true()
  dataplane/virtio-blk: drop flush_true() and flush_io()
  thread-pool: drop thread_pool_active()
  tests: drop event_active_cb()
  aio: drop io_flush argument

 aio-posix.c                     | 36 ++++++------------
 aio-win32.c                     | 37 ++++++++-----------
 async.c                         |  4 +-
 block.c                         | 47 ++++++++++++++++-------
 block/curl.c                    | 25 ++-----------
 block/gluster.c                 | 21 ++---------
 block/iscsi.c                   | 10 +----
 block/linux-aio.c               | 18 +--------
 block/nbd.c                     | 18 ++-------
 block/rbd.c                     | 16 +-------
 block/sheepdog.c                | 33 ++++-------------
 block/ssh.c                     | 12 +-----
 hw/block/dataplane/virtio-blk.c | 25 +++----------
 include/block/aio.h             | 11 +-----
 main-loop.c                     |  9 ++---
 tests/test-aio.c                | 82 +++++++++++++++++++++--------------------
 tests/test-thread-pool.c        | 24 ++++++------
 thread-pool.c                   | 11 +-----
 18 files changed, 155 insertions(+), 284 deletions(-)

-- 
1.8.1.4