Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Pull request

v2:
 * Rebased to resolve scsi conflicts

# gpg: Signature made Tue 21 Feb 2017 11:56:24 GMT
# gpg:                using RSA key 0x9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request: (24 commits)
  coroutine-lock: make CoRwlock thread-safe and fair
  coroutine-lock: add mutex argument to CoQueue APIs
  coroutine-lock: place CoMutex before CoQueue in header
  test-aio-multithread: add performance comparison with thread-based mutexes
  coroutine-lock: add limited spinning to CoMutex
  coroutine-lock: make CoMutex thread-safe
  block: document fields protected by AioContext lock
  async: remove unnecessary inc/dec pairs
  aio-posix: partially inline aio_dispatch into aio_poll
  block: explicitly acquire aiocontext in aio callbacks that need it
  block: explicitly acquire aiocontext in bottom halves that need it
  block: explicitly acquire aiocontext in callbacks that need it
  block: explicitly acquire aiocontext in timers that need it
  aio: push aio_context_acquire/release down to dispatching
  qed: introduce qed_aio_start_io and qed_aio_next_io_cb
  blkdebug: reschedule coroutine on the AioContext it is running on
  coroutine-lock: reschedule coroutine on the AioContext it was running on
  nbd: convert to use qio_channel_yield
  io: make qio_channel_yield aware of AioContexts
  io: add methods to set I/O handlers on AioContext
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 6444e41d39..f365a51acf 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -64,14 +64,20 @@ typedef struct BlockDevOps {
  * fields that must be public. This is in particular for QLIST_ENTRY() and
  * friends so that BlockBackends can be kept in lists outside block-backend.c */
 typedef struct BlockBackendPublic {
-    /* I/O throttling.
-     * throttle_state tells us if this BlockBackend has I/O limits configured.
-     * io_limits_disabled tells us if they are currently being enforced */
+    /* I/O throttling has its own locking, but also some fields are
+     * protected by the AioContext lock.
+     */
+
+    /* Protected by AioContext lock.  */
     CoQueue      throttled_reqs[2];
+
+    /* Nonzero if the I/O limits are currently being ignored; generally
+     * it is zero.  */
     unsigned int io_limits_disabled;
 
     /* The following fields are protected by the ThrottleGroup lock.
-     * See the ThrottleGroup documentation for details. */
+     * See the ThrottleGroup documentation for details.
+     * throttle_state tells us if I/O limits are configured. */
     ThrottleState *throttle_state;
     ThrottleTimers throttle_timers;
     unsigned       pending_reqs[2];