[PATCH] helper function for retrieving scsi_cmd given host based block layer tag

This was necessitated by the need for a function to get back
to a scsi_cmnd, when an hba the posts its (corresponding) completion
interrupt with a block layer tag as its reference.
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: David Somayajulu <david.somayajulu@qlogic.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/ll_rw_blk.c

@@ -840,12 +840,7 @@ EXPORT_SYMBOL(blk_queue_dma_alignment);
  **/
 struct request *blk_queue_find_tag(request_queue_t *q, int tag)
 {
-	struct blk_queue_tag *bqt = q->queue_tags;
-
-	if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
-		return NULL;
-
-	return bqt->tag_index[tag];
+	return blk_map_queue_find_tag(q->queue_tags, tag);
 }
 
 EXPORT_SYMBOL(blk_queue_find_tag);

include/linux/blkdev.h

@@ -769,6 +769,14 @@ extern struct blk_queue_tag *blk_init_tags(int);
 extern void blk_free_tags(struct blk_queue_tag *);
 extern void blk_congestion_end(int rw);
 
+static inline struct request *blk_map_queue_find_tag(struct blk_queue_tag *bqt,
+						int tag)
+{
+	if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
+		return NULL;
+	return bqt->tag_index[tag];
+}
+
 extern void blk_rq_bio_prep(request_queue_t *, struct request *, struct bio *);
 extern int blkdev_issue_flush(struct block_device *, sector_t *);
 

include/scsi/scsi_tcq.h

@@ -144,5 +144,25 @@ static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
 	return shost->bqt ? 0 : -ENOMEM;
 }
 
+/**
+ * scsi_host_find_tag - find the tagged command by host
+ * @shost:	pointer to scsi_host
+ * @tag:	tag of the scsi_cmnd
+ *
+ * Notes:
+ *	Only works with tags allocated by the generic blk layer.
+ **/
+static inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
+						int tag)
+{
+	struct request *req;
+
+	if (tag != SCSI_NO_TAG) {
+		req = blk_map_queue_find_tag(shost->bqt, tag);
+		return req ? (struct scsi_cmnd *)req->special : NULL;
+	}
+	return NULL;
+}
+
 #endif /* CONFIG_BLOCK */
 #endif /* _SCSI_SCSI_TCQ_H */