block: Convert bdrv_refresh_total_sectors() to co_wrapper_mixed

BlockDriver->bdrv_getlength is categorized as IO callback, and it
currently doesn't run in a coroutine. We should let it take a graph
rdlock since the callback traverses the block nodes graph, which however
is only possible in a coroutine.

Therefore turn it into a co_wrapper to move the actual function into a
coroutine where the lock can be taken.

Because now this function creates a new coroutine and polls, we need to
take the AioContext lock where it is missing, for the only reason that
internally co_wrapper calls AIO_WAIT_WHILE and it expects to release the
AioContext lock.

This is especially messy when a co_wrapper creates a coroutine and polls
in bdrv_open_driver, because this function has so many callers in so
many context that it can easily lead to deadlocks. Therefore the new
rule for bdrv_open_driver is that the caller must always hold the
AioContext lock of the given bs (except if it is a coroutine), because
the function calls bdrv_refresh_total_sectors() which is now a
co_wrapper.

Once the rwlock is ultimated and placed in every place it needs to be,
we will poll using AIO_WAIT_WHILE_UNLOCKED and remove the AioContext
lock.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230113204212.359076-7-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/block/raw-format.c b/block/raw-format.c
index b6a0ce5..836190a 100644
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -317,14 +317,14 @@ static int coroutine_fn raw_co_pdiscard(BlockDriverState *bs,
     return bdrv_co_pdiscard(bs->file, offset, bytes);
 }
 
-static int64_t raw_getlength(BlockDriverState *bs)
+static int64_t coroutine_fn raw_co_getlength(BlockDriverState *bs)
 {
     int64_t len;
     BDRVRawState *s = bs->opaque;
 
     /* Update size. It should not change unless the file was externally
      * modified. */
-    len = bdrv_getlength(bs->file->bs);
+    len = bdrv_co_getlength(bs->file->bs);
     if (len < 0) {
         return len;
     }
@@ -622,7 +622,7 @@ BlockDriver bdrv_raw = {
     .bdrv_co_copy_range_from = &raw_co_copy_range_from,
     .bdrv_co_copy_range_to  = &raw_co_copy_range_to,
     .bdrv_co_truncate     = &raw_co_truncate,
-    .bdrv_getlength       = &raw_getlength,
+    .bdrv_co_getlength    = &raw_co_getlength,
     .is_format            = true,
     .has_variable_length  = true,
     .bdrv_measure         = &raw_measure,