add a struct request pointer to the request structure

This adds a struct request pointer to the request structure for the
second data phase (bidi for now). A request queue supporting bidi
requests sets QUEUE_FLAG_BIDI. This prevents sending bidi requests to
a non-bidi queue.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/ll_rw_blk.c

@@ -256,6 +256,7 @@ static void rq_init(request_queue_t *q, struct request *rq)
 	rq->end_io = NULL;
 	rq->end_io_data = NULL;
 	rq->completion_data = NULL;
+	rq->next_rq = NULL;
 }
 
 /**

include/linux/blkdev.h

@@ -317,6 +317,9 @@ struct request {
 	 */
 	rq_end_io_fn *end_io;
 	void *end_io_data;
+
+	/* for bidi */
+	struct request *next_rq;
 };
 
 /*
@@ -486,6 +489,7 @@ struct request_queue
 #define QUEUE_FLAG_REENTER	6	/* Re-entrancy avoidance */
 #define QUEUE_FLAG_PLUGGED	7	/* queue is plugged */
 #define QUEUE_FLAG_ELVSWITCH	8	/* don't use elevator, just do FIFO */
+#define QUEUE_FLAG_BIDI		9	/* queue supports bidi requests */
 
 enum {
 	/*
@@ -550,6 +554,7 @@ enum {
 #define blk_sorted_rq(rq)	((rq)->cmd_flags & REQ_SORTED)
 #define blk_barrier_rq(rq)	((rq)->cmd_flags & REQ_HARDBARRIER)
 #define blk_fua_rq(rq)		((rq)->cmd_flags & REQ_FUA)
+#define blk_bidi_rq(rq)		((rq)->next_rq != NULL)
 
 #define list_entry_rq(ptr)	list_entry((ptr), struct request, queuelist)