[PATCH] Consolidate SCSI requeueing and add blk elevator hook

This patch removes the scsi mid layer dependency on __elv_add_request
and introduces a new blk_requeue_request() function so the block
layer specificially knows a requeue is in progress.

It also adds an elevator hook for elevators like AS which need to
hook into the requeue for correct adjustment of internal counters.

drivers/block/elevator.c

@@ -214,6 +214,18 @@ void elv_merge_requests(request_queue_t *q, struct request *rq,
 		e->elevator_merge_req_fn(q, rq, next);
 }
 
+void elv_requeue_request(request_queue_t *q, struct request *rq)
+{
+	/*
+	 * if iosched has an explicit requeue hook, then use that. otherwise
+	 * just put the request at the front of the queue
+	 */
+	if (q->elevator.elevator_requeue_req_fn)
+		q->elevator.elevator_requeue_req_fn(q, rq);
+	else
+		__elv_add_request(q, rq, 0, 0);
+}
+
 void __elv_add_request(request_queue_t *q, struct request *rq, int at_end,
 		       int plug)
 {
@@ -405,6 +417,7 @@ EXPORT_SYMBOL(elevator_noop);
 
 EXPORT_SYMBOL(elv_add_request);
 EXPORT_SYMBOL(__elv_add_request);
+EXPORT_SYMBOL(elv_requeue_request);
 EXPORT_SYMBOL(elv_next_request);
 EXPORT_SYMBOL(elv_remove_request);
 EXPORT_SYMBOL(elv_queue_empty);

drivers/block/ll_rw_blk.c

@@ -1355,6 +1355,23 @@ struct request *blk_get_request(request_queue_t *q, int rw, int gfp_mask)
 
 	return rq;
 }
+/**
+ * blk_requeue_request - put a request back on queue
+ * @q:		request queue where request should be inserted
+ * @rq:		request to be inserted
+ *
+ * Description:
+ *    Drivers often keep queueing requests until the hardware cannot accept
+ *    more, when that condition happens we need to put the request back
+ *    on the queue. Must be called with queue lock held.
+ */
+void blk_requeue_request(request_queue_t *q, struct request *rq)
+{
+	if (blk_rq_tagged(rq))
+		blk_queue_end_tag(q, rq);
+
+	elv_requeue_request(q, rq);
+}
 
 /**
  * blk_insert_request - insert a special request in to a request queue
@@ -2339,6 +2356,7 @@ EXPORT_SYMBOL(blk_hw_contig_segment);
 EXPORT_SYMBOL(blk_get_request);
 EXPORT_SYMBOL(blk_put_request);
 EXPORT_SYMBOL(blk_insert_request);
+EXPORT_SYMBOL(blk_requeue_request);
 
 EXPORT_SYMBOL(blk_queue_prep_rq);
 EXPORT_SYMBOL(blk_queue_merge_bvec);

drivers/scsi/scsi_lib.c

@@ -444,22 +444,8 @@ static void scsi_run_queue(struct request_queue *q)
  */
 static void scsi_requeue_command(struct request_queue *q, struct scsi_cmnd *cmd)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(q->queue_lock, flags);
-	cmd->request->special = cmd;
-	if (blk_rq_tagged(cmd->request))
-		blk_queue_end_tag(q, cmd->request);
-
-	/*
-	 * set REQ_SPECIAL - we have a command
-	 * clear REQ_DONTPREP - we assume the sg table has been 
-	 *	nuked so we need to set it up again.
-	 */
-	cmd->request->flags |= REQ_SPECIAL;
 	cmd->request->flags &= ~REQ_DONTPREP;
-	__elv_add_request(q, cmd->request, 0, 0);
-	spin_unlock_irqrestore(q->queue_lock, flags);
+	blk_insert_request(q, cmd->request, 1, cmd);
 
 	scsi_run_queue(q);
 }
@@ -1213,9 +1199,7 @@ static void scsi_request_fn(struct request_queue *q)
 	 * later time.
 	 */
 	spin_lock_irq(q->queue_lock);
-	if (blk_rq_tagged(req))
-		blk_queue_end_tag(q, req);
-	__elv_add_request(q, req, 0, 0);
+	blk_requeue_request(q, req);
 	sdev->device_busy--;
 	if(sdev->device_busy == 0)
 		blk_plug_device(q);

include/linux/blkdev.h

@@ -405,6 +405,7 @@ extern void __blk_attempt_remerge(request_queue_t *, struct request *);
 extern struct request *blk_get_request(request_queue_t *, int, int);
 extern void blk_put_request(struct request *);
 extern void blk_insert_request(request_queue_t *, struct request *, int, void *);
+extern void blk_requeue_request(request_queue_t *, struct request *);
 extern void blk_plug_device(request_queue_t *);
 extern int blk_remove_plug(request_queue_t *);
 extern void blk_recount_segments(request_queue_t *, struct bio *);

include/linux/elevator.h

@@ -13,6 +13,7 @@ typedef struct request *(elevator_next_req_fn) (request_queue_t *);
 typedef void (elevator_add_req_fn) (request_queue_t *, struct request *, struct list_head *);
 typedef int (elevator_queue_empty_fn) (request_queue_t *);
 typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
+typedef void (elevator_requeue_req_fn) (request_queue_t *, struct request *);
 typedef struct request *(elevator_request_list_fn) (request_queue_t *, struct request *);
 typedef struct list_head *(elevator_get_sort_head_fn) (request_queue_t *, struct request *);
 typedef int (elevator_set_req_fn) (request_queue_t *, struct request *, int);
@@ -30,6 +31,7 @@ struct elevator_s
 	elevator_next_req_fn *elevator_next_req_fn;
 	elevator_add_req_fn *elevator_add_req_fn;
 	elevator_remove_req_fn *elevator_remove_req_fn;
+	elevator_requeue_req_fn *elevator_requeue_req_fn;
 
 	elevator_queue_empty_fn *elevator_queue_empty_fn;
 
@@ -58,6 +60,7 @@ extern void elv_merge_requests(request_queue_t *, struct request *,
 			       struct request *);
 extern void elv_merged_request(request_queue_t *, struct request *);
 extern void elv_remove_request(request_queue_t *, struct request *);
+extern void elv_requeue_request(request_queue_t *, struct request *);
 extern int elv_queue_empty(request_queue_t *);
 extern struct request *elv_next_request(struct request_queue *q);
 extern struct request *elv_former_request(request_queue_t *, struct request *);