[PATCH v1 4/4] block: link request queue debugfs directories to tag sets

[Lei Chen]

Tag set debugfs directories use numeric IDs that do not identify their
attached disks. Starting from a disk's debugfs directory therefore gives
no direct way to find its tag set configuration and CPU mappings.

Add a tagset symlink in each blk-mq request queue's debugfs directory,
pointing to ../../tagset/<id>. Queues sharing a tag set link to the same
directory. Create the link only when both debugfs directories exist.

Signed-off-by: Lei Chen <lei.chen@xxxxxxxxxx>
---
 block/blk-mq-debugfs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 298387607049..78a91a1095bb 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -644,11 +644,19 @@ static void debugfs_create_files(struct request_queue *q, struct dentry *parent,
 
 void blk_mq_debugfs_register(struct request_queue *q)
 {
+	struct blk_mq_tag_set *set = q->tag_set;
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
+	char target[32];
 
 	debugfs_create_files(q, q->debugfs_dir, q, blk_mq_debugfs_queue_attrs);
 
+	if (!IS_ERR_OR_NULL(q->debugfs_dir) &&
+	    !IS_ERR_OR_NULL(set->debugfs_dir) && set->debugfs_id >= 0) {
+		snprintf(target, sizeof(target), "../../tagset/%d", set->debugfs_id);
+		debugfs_create_symlink("tagset", q->debugfs_dir, target);
+	}
+
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (!hctx->debugfs_dir)
 			blk_mq_debugfs_register_hctx(q, hctx);
-- 
2.43.0