block: misc cleanups in barrier code

Make the following cleanups in preparation of barrier/flush update.

* blk_do_ordered() declaration is moved from include/linux/blkdev.h to
  block/blk.h.

* blk_do_ordered() now returns pointer to struct request, with %NULL
  meaning "try the next request" and ERR_PTR(-EAGAIN) "try again
  later".  The third case will be dropped with further changes.

* In the initialization of proxy barrier request, data direction is
  already set by init_request_from_bio().  Drop unnecessary explicit
  REQ_WRITE setting and move init_request_from_bio() above REQ_FUA
  flag setting.

* add_request() is collapsed into __make_request().

These changes don't make any functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/blk-barrier.c

@@ -110,9 +110,9 @@ static void queue_flush(struct request_queue *q, unsigned which)
 	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 }
 
-static inline bool start_ordered(struct request_queue *q, struct request **rqp)
+static inline struct request *start_ordered(struct request_queue *q,
+					    struct request *rq)
 {
-	struct request *rq = *rqp;
 	unsigned skip = 0;
 
 	q->orderr = 0;
@@ -149,11 +149,9 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
 
 		/* initialize proxy request and queue it */
 		blk_rq_init(q, rq);
-		if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
-			rq->cmd_flags |= REQ_WRITE;
+		init_request_from_bio(rq, q->orig_bar_rq->bio);
 		if (q->ordered & QUEUE_ORDERED_DO_FUA)
 			rq->cmd_flags |= REQ_FUA;
-		init_request_from_bio(rq, q->orig_bar_rq->bio);
 		rq->end_io = bar_end_io;
 
 		elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
@@ -171,36 +169,34 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
 	else
 		skip |= QUEUE_ORDSEQ_DRAIN;
 
-	*rqp = rq;
-
 	/*
 	 * Complete skipped sequences.  If whole sequence is complete,
-	 * return false to tell elevator that this request is gone.
+	 * return %NULL to tell elevator that this request is gone.
 	 */
-	return !blk_ordered_complete_seq(q, skip, 0);
+	if (blk_ordered_complete_seq(q, skip, 0))
+		rq = NULL;
+	return rq;
 }
 
-bool blk_do_ordered(struct request_queue *q, struct request **rqp)
+struct request *blk_do_ordered(struct request_queue *q, struct request *rq)
 {
-	struct request *rq = *rqp;
 	const int is_barrier = rq->cmd_type == REQ_TYPE_FS &&
 				(rq->cmd_flags & REQ_HARDBARRIER);
 
 	if (!q->ordseq) {
 		if (!is_barrier)
-			return true;
+			return rq;
 
 		if (q->next_ordered != QUEUE_ORDERED_NONE)
-			return start_ordered(q, rqp);
+			return start_ordered(q, rq);
 		else {
 			/*
 			 * Queue ordering not supported.  Terminate
 			 * with prejudice.
 			 */
 			blk_dequeue_request(rq);
 			__blk_end_request_all(rq, -EOPNOTSUPP);
-			*rqp = NULL;
-			return false;
+			return NULL;
 		}
 	}
 
@@ -211,14 +207,14 @@ bool blk_do_ordered(struct request_queue *q, struct request **rqp)
 	/* Special requests are not subject to ordering rules. */
 	if (rq->cmd_type != REQ_TYPE_FS &&
 	    rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
-		return true;
+		return rq;
 
 	/* Ordered by draining.  Wait for turn. */
 	WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
 	if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
-		*rqp = NULL;
+		rq = ERR_PTR(-EAGAIN);
 
-	return true;
+	return rq;
 }
 
 static void bio_end_empty_barrier(struct bio *bio, int err)

block/blk-core.c

@@ -1037,22 +1037,6 @@ void blk_insert_request(struct request_queue *q, struct request *rq,
 }
 EXPORT_SYMBOL(blk_insert_request);
 
-/*
- * add-request adds a request to the linked list.
- * queue lock is held and interrupts disabled, as we muck with the
- * request queue list.
- */
-static inline void add_request(struct request_queue *q, struct request *req)
-{
-	drive_stat_acct(req, 1);
-
-	/*
-	 * elevator indicated where it wants this request to be
-	 * inserted at elevator_merge time
-	 */
-	__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
-}
-
 static void part_round_stats_single(int cpu, struct hd_struct *part,
 				    unsigned long now)
 {
@@ -1316,7 +1300,10 @@ static int __make_request(struct request_queue *q, struct bio *bio)
 		req->cpu = blk_cpu_to_group(smp_processor_id());
 	if (queue_should_plug(q) && elv_queue_empty(q))
 		blk_plug_device(q);
-	add_request(q, req);
+
+	/* insert the request into the elevator */
+	drive_stat_acct(req, 1);
+	__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
 out:
 	if (unplug || !queue_should_plug(q))
 		__generic_unplug_device(q);

block/blk.h

@@ -51,15 +51,18 @@ static inline void blk_clear_rq_complete(struct request *rq)
  */
 #define ELV_ON_HASH(rq)		(!hlist_unhashed(&(rq)->hash))
 
+struct request *blk_do_ordered(struct request_queue *q, struct request *rq);
+
 static inline struct request *__elv_next_request(struct request_queue *q)
 {
 	struct request *rq;
 
 	while (1) {
 		while (!list_empty(&q->queue_head)) {
 			rq = list_entry_rq(q->queue_head.next);
-			if (blk_do_ordered(q, &rq))
-				return rq;
+			rq = blk_do_ordered(q, rq);
+			if (rq)
+				return !IS_ERR(rq) ? rq : NULL;
 		}
 
 		if (!q->elevator->ops->elevator_dispatch_fn(q, 0))

include/linux/blkdev.h

@@ -869,7 +869,6 @@ extern void blk_queue_rq_timed_out(struct request_queue *, rq_timed_out_fn *);
 extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
 extern void blk_queue_flush(struct request_queue *q, unsigned int flush);
 extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
-extern bool blk_do_ordered(struct request_queue *, struct request **);
 extern unsigned blk_ordered_cur_seq(struct request_queue *);
 extern unsigned blk_ordered_req_seq(struct request *);
 extern bool blk_ordered_complete_seq(struct request_queue *, unsigned, int);