block: bdrv_aligned_pwritev: Assert overlap range

This adds assertions that the request that we actually end up passing to
the block driver (which includes RMW data and has therefore potentially
been rounded to alignment boundaries) is fully covered by the
overlap_{offset,size} fields of the associated BdrvTrackedRequest.
Suggested-by: NLaszlo Ersek <lersek@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>

block.c

@@ -3134,6 +3134,8 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
 
     waited = wait_serialising_requests(req);
     assert(!waited || !req->serialising);
+    assert(req->overlap_offset <= offset);
+    assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
 
     ret = notifier_with_return_list_notify(&bs->before_write_notifiers, req);