[PATCH V3 3/8] blk-mq: introduce 'start_tag' field to 'struct blk_mq_tags'

[Ming Lei <ming.lei@redhat.com>]

This patch introduces 'start_tag' field to 'struct blk_mq_tags' so that
host wide tagset can be supported easily in the following patches by
partitioning host wide tags into multiple hw queues.

No function change.

Cc: Hannes Reinecke <hare@suse.de>
Cc: Arun Easi <arun.easi@cavium.com>
Cc: Omar Sandoval <osandov@fb.com>,
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
Cc: James Bottomley <james.bottomley@hansenpartnership.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: Don Brace <don.brace@microsemi.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Peter Rivera <peter.rivera@broadcom.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-tag.c | 3 ++-
 block/blk-mq-tag.h | 6 ++++--
 block/blk-mq.c     | 7 ++++---
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 336dde07b230..5014d7343ea9 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -179,12 +179,13 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 	finish_wait(&ws->wait, &wait);
 
 found_tag:
-	return tag + tag_offset;
+	return tag + tag_offset + tags->start_tag;
 }
 
 void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_tags *tags,
 		    struct blk_mq_ctx *ctx, unsigned int tag)
 {
+	tag -= tags->start_tag;
 	if (!blk_mq_tag_is_reserved(tags, tag)) {
 		const int real_tag = tag - tags->nr_reserved_tags;
 
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 61deab0b5a5a..1d629920db69 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -13,6 +13,8 @@ struct blk_mq_tags {
 
 	atomic_t active_queues;
 
+	unsigned int start_tag;
+
 	struct sbitmap_queue bitmap_tags;
 	struct sbitmap_queue breserved_tags;
 
@@ -78,13 +80,13 @@ static inline void blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 static inline void blk_mq_tag_set_rq(struct blk_mq_hw_ctx *hctx,
 		unsigned int tag, struct request *rq)
 {
-	hctx->tags->rqs[tag] = rq;
+	hctx->tags->rqs[tag - hctx->tags->start_tag] = rq;
 }
 
 static inline bool blk_mq_tag_is_reserved(struct blk_mq_tags *tags,
 					  unsigned int tag)
 {
-	return tag < tags->nr_reserved_tags;
+	return (tag - tags->start_tag) < tags->nr_reserved_tags;
 }
 
 #endif
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 357492712b0e..5ea11d087f7b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -270,7 +270,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 		unsigned int tag, unsigned int op)
 {
 	struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
-	struct request *rq = tags->static_rqs[tag];
+	struct request *rq = tags->static_rqs[tag - tags->start_tag];
 	req_flags_t rq_flags = 0;
 
 	if (data->flags & BLK_MQ_REQ_INTERNAL) {
@@ -283,7 +283,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 		}
 		rq->tag = tag;
 		rq->internal_tag = -1;
-		data->hctx->tags->rqs[rq->tag] = rq;
+		data->hctx->tags->rqs[rq->tag - tags->start_tag] = rq;
 	}
 
 	/* csd/requeue_work/fifo_time is initialized before use */
@@ -801,6 +801,7 @@ EXPORT_SYMBOL(blk_mq_delay_kick_requeue_list);
 
 struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
 {
+	tag -= tags->start_tag;
 	if (tag < tags->nr_tags) {
 		prefetch(tags->rqs[tag]);
 		return tags->rqs[tag];
@@ -1076,7 +1077,7 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
 			rq->rq_flags |= RQF_MQ_INFLIGHT;
 			atomic_inc(&data.hctx->nr_active);
 		}
-		data.hctx->tags->rqs[rq->tag] = rq;
+		data.hctx->tags->rqs[rq->tag - data.hctx->tags->start_tag] = rq;
 	}
 
 done:
-- 
2.9.5