[Qemu-devel] [PATCH v6 00/18] aio: drop io_flush()

[Stefan Hajnoczi]

v6:
 * Fix block/stream.c:close_unused_images() dangling pointer in Patch 2
 * Rebase onto qemu.git/master

v5:
 * Split out bdrv_delete() drain fix [bonzini]
 * Fix commit message  [bonzini]

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 possible to unify AioContext and
main-loop.c, maybe even to replace it with glib's main loop.

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():

  bcfa688 block: ensure bdrv_drain_all() works during bdrv_delete()
  c1351f5 block: stop relying on io_flush() in bdrv_drain_all()
  b75d9e5 dataplane/virtio-blk: check exit conditions before aio_poll()
  18fc4d6 tests: adjust test-aio to new aio_poll() semantics
  4c52a7c 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:

  bacae7a 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:

  720e0ad block/curl: drop curl_aio_flush()
  2830cf3 block/gluster: drop qemu_gluster_aio_flush_cb()
  c683e8e block/iscsi: drop iscsi_process_flush()
  5019686 block/linux-aio: drop qemu_laio_completion_cb()
  b862bcf block/nbd: drop nbd_have_request()
  516e517 block/rbd: drop qemu_rbd_aio_flush_cb()
  177090b block/sheepdog: drop have_co_req() and aio_flush_request()
  e2e9e85 block/ssh: drop return_true()
  7cc7bac dataplane/virtio-blk: drop flush_true() and flush_io()
  db3cb18 thread-pool: drop thread_pool_active()
  10a783b tests: drop event_active_cb()

Part 4 - remove io_flush arguments from aio functions

The big, mechanical patch that drops the io_flush argument:

  4a8c36b 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 (18):
  block: ensure bdrv_drain_all() works during bdrv_delete()
  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 +-----
 block/stream.c                  |  6 ++-
 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 +-----
 19 files changed, 163 insertions(+), 288 deletions(-)

-- 
1.8.1.4