blk-mq: allow changing of queue depth through sysfs

For request_fn based devices, the block layer exports a 'nr_requests'
file through sysfs to allow adjusting of queue depth on the fly.
Currently this returns -EINVAL for blk-mq, since it's not wired up.
Wire this up for blk-mq, so that it now also always dynamic
adjustments of the allowed queue depth for any given block device
managed by blk-mq.

Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0fbef7e9bef1..7b71ab1b1536 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1789,6 +1789,28 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 }
 EXPORT_SYMBOL(blk_mq_free_tag_set);
 
+int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
+{
+	struct blk_mq_tag_set *set = q->tag_set;
+	struct blk_mq_hw_ctx *hctx;
+	int i, ret;
+
+	if (!set || nr > set->queue_depth)
+		return -EINVAL;
+
+	ret = 0;
+	queue_for_each_hw_ctx(q, hctx, i) {
+		ret = blk_mq_tag_update_depth(hctx->tags, nr);
+		if (ret)
+			break;
+	}
+
+	if (!ret)
+		q->nr_requests = nr;
+
+	return ret;
+}
+
 void blk_mq_disable_hotplug(void)
 {
 	mutex_lock(&all_q_mutex);