block: Revert .bdrv_drained_begin/end to non-coroutine_fn

Polling during bdrv_drained_end() can be problematic (and in the future,
we may get cases for bdrv_drained_begin() where polling is forbidden,
and we don't care about already in-flight requests, but just want to
prevent new requests from arriving).

The .bdrv_drained_begin/end callbacks running in a coroutine is the only
reason why we have to do this polling, so make them non-coroutine
callbacks again. None of the callers actually yield any more.

This means that bdrv_drained_end() effectively doesn't poll any more,
even if AIO_WAIT_WHILE() loops are still there (their condition is false
from the beginning). This is generally not a problem, but in
test-bdrv-drain, some additional explicit aio_poll() calls need to be
added because the test case wants to verify the final state after BHs
have executed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20221118174110.55183-4-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 31ae91e..40d646d 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -735,17 +735,19 @@ struct BlockDriver {
     void (*bdrv_io_unplug)(BlockDriverState *bs);
 
     /**
-     * bdrv_co_drain_begin is called if implemented in the beginning of a
+     * bdrv_drain_begin is called if implemented in the beginning of a
      * drain operation to drain and stop any internal sources of requests in
      * the driver.
-     * bdrv_co_drain_end is called if implemented at the end of the drain.
+     * bdrv_drain_end is called if implemented at the end of the drain.
      *
      * They should be used by the driver to e.g. manage scheduled I/O
      * requests, or toggle an internal state. After the end of the drain new
      * requests will continue normally.
+     *
+     * Implementations of both functions must not call aio_poll().
      */
-    void coroutine_fn (*bdrv_co_drain_begin)(BlockDriverState *bs);
-    void coroutine_fn (*bdrv_co_drain_end)(BlockDriverState *bs);
+    void (*bdrv_drain_begin)(BlockDriverState *bs);
+    void (*bdrv_drain_end)(BlockDriverState *bs);
 
     bool (*bdrv_supports_persistent_dirty_bitmap)(BlockDriverState *bs);
     bool coroutine_fn (*bdrv_co_can_store_new_dirty_bitmap)(