[PATCH] shared block queue tag map

This implements the possibility for sharing a tag map between queues.
Some (most?) scsi host adapters needs this, and SATA tcq will need it
for some cases, too.

drivers/block/ll_rw_blk.c

@@ -458,16 +458,19 @@ void blk_queue_free_tags(request_queue_t *q)
 	if (!bqt)
 		return;
 
-	BUG_ON(bqt->busy);
-	BUG_ON(!list_empty(&bqt->busy_list));
+	if (atomic_dec_and_test(&bqt->refcnt)) {
+		BUG_ON(bqt->busy);
+		BUG_ON(!list_empty(&bqt->busy_list));
 
-	kfree(bqt->tag_index);
-	bqt->tag_index = NULL;
+		kfree(bqt->tag_index);
+		bqt->tag_index = NULL;
 
-	kfree(bqt->tag_map);
-	bqt->tag_map = NULL;
+		kfree(bqt->tag_map);
+		bqt->tag_map = NULL;
+
+		kfree(bqt);
+	}
 
-	kfree(bqt);
 	q->queue_tags = NULL;
 	q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
 }
@@ -503,6 +506,9 @@ init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
 	for (i = depth; i < bits * BLK_TAGS_PER_LONG; i++)
 		__set_bit(i, tags->tag_map);
 
+	INIT_LIST_HEAD(&tags->busy_list);
+	tags->busy = 0;
+	atomic_set(&tags->refcnt, 1);
 	return 0;
 fail:
 	kfree(tags->tag_index);
@@ -514,19 +520,18 @@ init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
  * @q:  the request queue for the device
  * @depth:  the maximum queue depth supported
  **/
-int blk_queue_init_tags(request_queue_t *q, int depth)
+int blk_queue_init_tags(request_queue_t *q, int depth,
+			struct blk_queue_tag *tags)
 {
-	struct blk_queue_tag *tags;
-
-	tags = kmalloc(sizeof(struct blk_queue_tag),GFP_ATOMIC);
-	if (!tags)
-		goto fail;
+	if (!tags) {
+		tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
+		if (!tags)
+			goto fail;
 
-	if (init_tag_map(q, tags, depth))
-		goto fail;
-
-	INIT_LIST_HEAD(&tags->busy_list);
-	tags->busy = 0;
+		if (init_tag_map(q, tags, depth))
+			goto fail;
+	} else
+		atomic_inc(&tags->refcnt);
 
 	/*
 	 * assign it, all done

drivers/ide/ide-tcq.c

@@ -596,7 +596,7 @@ static int ide_enable_queued(ide_drive_t *drive, int on)
 	 * enable block tagging
 	 */
 	if (!blk_queue_tagged(drive->queue))
-		blk_queue_init_tags(drive->queue, IDE_MAX_TAG);
+		blk_queue_init_tags(drive->queue, IDE_MAX_TAG, NULL);
 
 	/*
 	 * check auto-poll support

include/linux/blkdev.h

@@ -262,6 +262,7 @@ struct blk_queue_tag {
 	int busy;			/* current depth */
 	int max_depth;			/* what we will send to device */
 	int real_max_depth;		/* what the array can hold */
+	atomic_t refcnt;		/* map can be shared */
 };
 
 struct request_queue
@@ -579,7 +580,7 @@ request_queue_t *blk_alloc_queue(int);
 extern int blk_queue_start_tag(request_queue_t *, struct request *);
 extern struct request *blk_queue_find_tag(request_queue_t *, int);
 extern void blk_queue_end_tag(request_queue_t *, struct request *);
-extern int blk_queue_init_tags(request_queue_t *, int);
+extern int blk_queue_init_tags(request_queue_t *, int, struct blk_queue_tag *);
 extern void blk_queue_free_tags(request_queue_t *);
 extern int blk_queue_resize_tags(request_queue_t *, int);
 extern void blk_queue_invalidate_tags(request_queue_t *);

include/scsi/scsi_tcq.h

@@ -27,7 +27,7 @@ static inline void scsi_activate_tcq(struct scsi_device *sdev, int depth)
 {
         if (sdev->tagged_supported) {
 		if (!blk_queue_tagged(sdev->request_queue))
-			blk_queue_init_tags(sdev->request_queue, depth);
+			blk_queue_init_tags(sdev->request_queue, depth, NULL);
 		scsi_adjust_queue_depth(sdev, MSG_ORDERED_TAG, depth);
         }
 }