[Qemu-devel] [PATCH v4 00/17] aio: drop io_flush()

[Stefan Hajnoczi]

v4:
 * Ensure pending BHs are processed in bdrv_drain_all() [bonzini]

v3:
 * I forgot about this series, time to push it again!
 * Rebase onto qemu.git/master
 * Drop now-unused AioFlushHandler typedef [bonzini]

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():

  76f9848 block: stop relying on io_flush() in bdrv_drain_all()
  42c7aac dataplane/virtio-blk: check exit conditions before aio_poll()
  b7c8b9a tests: adjust test-aio to new aio_poll() semantics
  55c7714 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:

  8f188ac 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:

  5967680 block/curl: drop curl_aio_flush()
  16ee264 block/gluster: drop qemu_gluster_aio_flush_cb()
  9563d0f block/iscsi: drop iscsi_process_flush()
  6690260 block/linux-aio: drop qemu_laio_completion_cb()
  3c30643 block/nbd: drop nbd_have_request()
  d47edee block/rbd: drop qemu_rbd_aio_flush_cb()
  edbf4b5 block/sheepdog: drop have_co_req() and aio_flush_request()
  3fee517 block/ssh: drop return_true()
  d59650d dataplane/virtio-blk: drop flush_true() and flush_io()
  0492713 thread-pool: drop thread_pool_active()
  77b3518 tests: drop event_active_cb()

Part 4 - remove io_flush arguments from aio functions

The big, mechanical patch that drops the io_flush argument:

  5938cf4 aio: drop io_flush argument

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                         | 50 ++++++++++++++++++-------
 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             | 14 +------
 main-loop.c                     |  9 ++---
 tests/test-aio.c                | 82 +++++++++++++++++++++--------------------
 tests/test-thread-pool.c        | 24 ++++++------
 thread-pool.c                   | 11 +-----
 18 files changed, 158 insertions(+), 287 deletions(-)

-- 
1.8.1.4