[PATCH v6 4/8] block: Make sub_page_limit_queues available in debugfs

[Bart Van Assche <bvanassche@xxxxxxx>]

This new debugfs attribute makes it easier to verify the code that tracks
how many queues require limits below the page size.

Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/blk-core.c       | 2 ++
 block/blk-mq-debugfs.c | 9 +++++++++
 block/blk-mq-debugfs.h | 6 ++++++
 block/blk-settings.c   | 8 ++++++++
 block/blk.h            | 1 +
 5 files changed, 26 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 73b8b547ecb9..ef6173ad4731 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -45,6 +45,7 @@
 #include <trace/events/block.h>
 
 #include "blk.h"
+#include "blk-mq-debugfs.h"
 #include "blk-mq-sched.h"
 #include "blk-pm.h"
 #include "blk-cgroup.h"
@@ -1204,6 +1205,7 @@ int __init blk_dev_init(void)
 			sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
 
 	blk_debugfs_root = debugfs_create_dir("block", NULL);
+	blk_mq_debugfs_init();
 
 	return 0;
 }
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index c3b5930106b2..5649c9e3719d 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -846,3 +846,12 @@ void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx)
 	debugfs_remove_recursive(hctx->sched_debugfs_dir);
 	hctx->sched_debugfs_dir = NULL;
 }
+
+DEFINE_DEBUGFS_ATTRIBUTE(blk_sub_page_limit_queues_fops,
+			blk_sub_page_limit_queues_get, NULL, "%llu\n");
+
+void blk_mq_debugfs_init(void)
+{
+	debugfs_create_file("sub_page_limit_queues", 0400, blk_debugfs_root,
+			    NULL, &blk_sub_page_limit_queues_fops);
+}
diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
index 9c7d4b6117d4..7942119051f5 100644
--- a/block/blk-mq-debugfs.h
+++ b/block/blk-mq-debugfs.h
@@ -17,6 +17,8 @@ struct blk_mq_debugfs_attr {
 	const struct seq_operations *seq_ops;
 };
 
+void blk_mq_debugfs_init(void);
+
 int __blk_mq_debugfs_rq_show(struct seq_file *m, struct request *rq);
 int blk_mq_debugfs_rq_show(struct seq_file *m, void *v);
 
@@ -36,6 +38,10 @@ void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx);
 void blk_mq_debugfs_register_rqos(struct rq_qos *rqos);
 void blk_mq_debugfs_unregister_rqos(struct rq_qos *rqos);
 #else
+static inline void blk_mq_debugfs_init(void)
+{
+}
+
 static inline void blk_mq_debugfs_register(struct request_queue *q)
 {
 }
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 607f21b99f3c..c1c4988cc575 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -107,6 +107,14 @@ void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce bounce)
 }
 EXPORT_SYMBOL(blk_queue_bounce_limit);
 
+/* For debugfs. */
+int blk_sub_page_limit_queues_get(void *data, u64 *val)
+{
+	*val = READ_ONCE(blk_nr_sub_page_limit_queues);
+
+	return 0;
+}
+
 /**
  * blk_enable_sub_page_limits - enable support for limits below the page size
  * @lim: request queue limits for which to enable support of these features.
diff --git a/block/blk.h b/block/blk.h
index d37ec737e05e..065449e7d0bd 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -39,6 +39,7 @@ static inline bool blk_queue_sub_page_limits(const struct queue_limits *lim)
 		lim->sub_page_limits;
 }
 
+int blk_sub_page_limit_queues_get(void *data, u64 *val);
 void blk_disable_sub_page_limits(struct queue_limits *q);
 
 void blk_freeze_queue(struct request_queue *q);