[PATCH v4 3/6] block: Introduce blk_mq_tagset_iter()

[Bart Van Assche <bvanassche@acm.org>]

Support iterating over all requests in a tag set, including requests
that have not yet been started. A later patch will call this function
from scsi_device_busy().

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-mq-tag.c     | 19 +++++++++++++++++++
 include/linux/blk-mq.h |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 783addc52e09..0e58e615af87 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -456,6 +456,25 @@ void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 }
 EXPORT_SYMBOL(blk_mq_tagset_busy_iter);
 
+/**
+ * blk_mq_tagset_iter - iterate over all requests in a tag set
+ * @tagset:	Tag set to iterate over.
+ * @fn:		Pointer to the function that will be called for each request.
+ *		@fn will be called as follows: @fn(rq, @priv) where rq is a
+ *		pointer to a request. Return true to continue iterating tags,
+ *		false to stop.
+ * @priv:	Will be passed as second argument to @fn.
+ *
+ * We grab one request reference before calling @fn and release it after
+ * @fn returns.
+ */
+void blk_mq_tagset_iter(struct blk_mq_tag_set *tagset, blk_mq_rq_iter_fn *fn,
+			void *priv)
+{
+	__blk_mq_tagset_iter(tagset, fn, priv, 0);
+}
+EXPORT_SYMBOL(blk_mq_tagset_iter);
+
 static bool blk_mq_tagset_count_completed_rqs(struct request *rq, void *data)
 {
 	unsigned *count = data;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3467cacb281c..20a22c1cd067 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -927,6 +927,8 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async);
 void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs);
 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 		blk_mq_rq_iter_fn *fn, void *priv);
+void blk_mq_tagset_iter(struct blk_mq_tag_set *tagset, blk_mq_rq_iter_fn *fn,
+		void *priv);
 void blk_mq_tagset_wait_completed_request(struct blk_mq_tag_set *tagset);
 void blk_mq_freeze_queue_nomemsave(struct request_queue *q);
 void blk_mq_unfreeze_queue_nomemrestore(struct request_queue *q);