[PATCH 1/4] block: provide helpers for rq_list manipulation

[Jens Axboe <axboe@xxxxxxxxx>]

Instead of open-coding the list additions, traversal, and removal,
provide a basic set of helpers.

Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 block/blk-mq.c         | 21 +++++----------------
 include/linux/blk-mq.h | 25 +++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6dfd3aaa6073..46a91e5fabc5 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -426,10 +426,10 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 			tag = tag_offset + i;
 			tags &= ~(1UL << i);
 			rq = blk_mq_rq_ctx_init(data, tag, alloc_time_ns);
-			rq->rq_next = *data->cached_rq;
-			*data->cached_rq = rq;
+			rq_list_add_tail(data->cached_rq, rq);
 		}
 		data->nr_tags -= nr;
+		return rq_list_pop(data->cached_rq);
 	} else {
 		/*
 		 * Waiting allocations only fail because of an inactive hctx.
@@ -453,14 +453,6 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 
 		return blk_mq_rq_ctx_init(data, tag, alloc_time_ns);
 	}
-
-	if (data->cached_rq) {
-		rq = *data->cached_rq;
-		*data->cached_rq = rq->rq_next;
-		return rq;
-	}
-
-	return NULL;
 }
 
 struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
@@ -603,11 +595,9 @@ EXPORT_SYMBOL_GPL(blk_mq_free_request);
 
 void blk_mq_free_plug_rqs(struct blk_plug *plug)
 {
-	while (plug->cached_rq) {
-		struct request *rq;
+	struct request *rq;
 
-		rq = plug->cached_rq;
-		plug->cached_rq = rq->rq_next;
+	while ((rq = rq_list_pop(&plug->cached_rq)) != NULL) {
 		percpu_ref_get(&rq->q->q_usage_counter);
 		blk_mq_free_request(rq);
 	}
@@ -2264,8 +2254,7 @@ void blk_mq_submit_bio(struct bio *bio)
 
 	plug = blk_mq_plug(q, bio);
 	if (plug && plug->cached_rq) {
-		rq = plug->cached_rq;
-		plug->cached_rq = rq->rq_next;
+		rq = rq_list_pop(&plug->cached_rq);
 		INIT_LIST_HEAD(&rq->queuelist);
 	} else {
 		struct blk_mq_alloc_data data = {
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index a9c1d0882550..c05560524841 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -473,6 +473,31 @@ struct blk_mq_tag_set {
 	struct list_head	tag_list;
 };
 
+#define rq_list_add_tail(listptr, rq)	do {		\
+	(rq)->rq_next = *(listptr);			\
+	*(listptr) = rq;				\
+} while (0)
+
+#define rq_list_pop(listptr)				\
+({							\
+	struct request *__req = NULL;			\
+	if ((listptr) && *(listptr))	{		\
+		__req = *(listptr);			\
+		*(listptr) = __req->rq_next;		\
+	}						\
+	__req;						\
+})
+
+#define rq_list_peek(listptr)				\
+({							\
+	struct request *__req = NULL;			\
+	if ((listptr) && *(listptr))			\
+		__req = *(listptr);			\
+	__req;						\
+})
+
+#define rq_list_next(rq)	(rq)->rq_next
+
 /**
  * struct blk_mq_queue_data - Data about a request inserted in a queue
  *
-- 
2.33.0