[PATCH] elv_add_request cleanups

Request insertion in the current tree is a mess. We have all sorts of
variants of *elv_add_request*, and it's not at all clear who does what
and with what locks (or not). This patch cleans it up to be:

o __elv_add_request(queue, request, at_end, plug)
      Core function, requires queue lock to be held

o elv_add_request(queue, request, at_end, plug)
      Like __elv_add_request(), but grabs queue lock

o __elv_add_request_pos(queue, request, position)
      Insert request at a given location, lock must be held

drivers/block/elevator.c

@@ -272,13 +272,27 @@ void elv_merge_requests(request_queue_t *q, struct request *rq,
 		e->elevator_merge_req_fn(q, rq, next);
 }
 
-/*
- * add_request and next_request are required to be supported, naturally
- */
-void __elv_add_request(request_queue_t *q, struct request *rq,
-			  struct list_head *insert_here)
+void __elv_add_request(request_queue_t *q, struct request *rq, int at_end,
+		       int plug)
+{
+	struct list_head *insert = &q->queue_head;
+
+	if (at_end)
+		insert = insert->prev;
+	if (plug)
+		blk_plug_device(q);
+
+	q->elevator.elevator_add_req_fn(q, rq, insert);
+}
+
+void elv_add_request(request_queue_t *q, struct request *rq, int at_end,
+		     int plug)
 {
-	q->elevator.elevator_add_req_fn(q, rq, insert_here);
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	__elv_add_request(q, rq, at_end, plug);
+	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
 static inline struct request *__elv_next_request(request_queue_t *q)
@@ -357,6 +371,7 @@ module_init(elevator_global_init);
 
 EXPORT_SYMBOL(elevator_noop);
 
+EXPORT_SYMBOL(elv_add_request);
 EXPORT_SYMBOL(__elv_add_request);
 EXPORT_SYMBOL(elv_next_request);
 EXPORT_SYMBOL(elv_remove_request);

drivers/block/ll_rw_blk.c

@@ -639,7 +639,7 @@ void blk_queue_invalidate_tags(request_queue_t *q)
 			blk_queue_end_tag(q, rq);
 
 		rq->flags &= ~REQ_STARTED;
-		elv_add_request(q, rq, 0);
+		__elv_add_request(q, rq, 0, 0);
 	}
 }
 
@@ -1466,7 +1466,7 @@ static inline void add_request(request_queue_t * q, struct request * req,
 	 * elevator indicated where it wants this request to be
 	 * inserted at elevator_merge time
 	 */
-	__elv_add_request(q, req, insert_here);
+	__elv_add_request_pos(q, req, insert_here);
 }
 
 /*

drivers/scsi/scsi_lib.c

@@ -240,7 +240,7 @@ void scsi_queue_next_request(request_queue_t * q, Scsi_Cmnd * SCpnt)
 		SCpnt->request->special = (void *) SCpnt;
 		if(blk_rq_tagged(SCpnt->request))
 			blk_queue_end_tag(q, SCpnt->request);
-		_elv_add_request(q, SCpnt->request, 0, 0);
+		__elv_add_request(q, SCpnt->request, 0, 0);
 	}
 
 	/*
@@ -951,7 +951,7 @@ void scsi_request_fn(request_queue_t * q)
 				SCpnt->request->flags |= REQ_SPECIAL;
 				if(blk_rq_tagged(SCpnt->request))
 					blk_queue_end_tag(q, SCpnt->request);
-				_elv_add_request(q, SCpnt->request, 0, 0);
+				__elv_add_request(q, SCpnt->request, 0, 0);
 				break;
 			}
 

include/linux/blk.h

@@ -50,22 +50,6 @@ static inline void blkdev_dequeue_request(struct request *req)
 		elv_remove_request(req->q, req);
 }
 
-#define _elv_add_request_core(q, rq, where, plug)			\
-	do {								\
-		if ((plug))						\
-			blk_plug_device((q));				\
-		(q)->elevator.elevator_add_req_fn((q), (rq), (where));	\
-	} while (0)
-
-#define _elv_add_request(q, rq, back, p) do {				      \
-	if ((back))							      \
-		_elv_add_request_core((q), (rq), (q)->queue_head.prev, (p));  \
-	else								      \
-		_elv_add_request_core((q), (rq), &(q)->queue_head, (p));      \
-} while (0)
-
-#define elv_add_request(q, rq, back) _elv_add_request((q), (rq), (back), 1)
-
 #if defined(MAJOR_NR) || defined(IDE_DRIVER)
 #if (MAJOR_NR != SCSI_TAPE_MAJOR) && (MAJOR_NR != OSST_MAJOR)
 #if !defined(IDE_DRIVER)

include/linux/elevator.h

@@ -40,8 +40,8 @@ struct elevator_s
 /*
  * block elevator interface
  */
-extern void __elv_add_request(request_queue_t *, struct request *,
-			      struct list_head *);
+extern void elv_add_request(request_queue_t *, struct request *, int, int);
+extern void __elv_add_request(request_queue_t *, struct request *, int, int);
 extern int elv_merge(request_queue_t *, struct list_head **, struct bio *);
 extern void elv_merge_requests(request_queue_t *, struct request *,
 			       struct request *);
@@ -50,6 +50,9 @@ extern void elv_remove_request(request_queue_t *, struct request *);
 extern int elv_queue_empty(request_queue_t *);
 extern inline struct list_head *elv_get_sort_head(request_queue_t *, struct request *);
 
+#define __elv_add_request_pos(q, rq, pos)	\
+	(q)->elevator.elevator_add_req_fn((q), (rq), (pos))
+
 /*
  * noop I/O scheduler. always merges, always inserts new request at tail
  */