block, drivers: add REQ_OP_FLUSH operation

This adds a REQ_OP_FLUSH operation that is sent to request_fn
based drivers by the block layer's flush code, instead of
sending requests with the request->cmd_flags REQ_FLUSH bit set.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
index 9fb26f2..d625311 100644
--- a/drivers/mmc/card/queue.h
+++ b/drivers/mmc/card/queue.h
@@ -3,7 +3,8 @@
 
 static inline bool mmc_req_is_special(struct request *req)
 {
-	return req && (req->cmd_flags & REQ_FLUSH || req_op(req) == REQ_OP_DISCARD);
+	return req &&
+		(req_op(req) == REQ_OP_FLUSH || req_op(req) == REQ_OP_DISCARD);
 }
 
 struct request;