blk-mq: fix debugfs compilation issues

This fixes a couple of problems:

1. In the !CONFIG_DEBUG_FS case, the stub definitions were bogus.
2. In the !CONFIG_BLOCK case, blk-mq-debugfs.c shouldn't be compiled at
   all.

Fix the stub definitions and add a CONFIG_BLK_DEBUG_FS Kconfig option.

Fixes: 07e4fead ("blk-mq: create debugfs directory tree")
Signed-off-by: Omar Sandoval <osandov@fb.com>

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

block/Kconfig

@@ -147,6 +147,18 @@ config BLK_WBT_MQ
 	Multiqueue currently doesn't have support for IO scheduling,
 	enabling this option is recommended.
 
+config BLK_DEBUG_FS
+	bool "Block layer debugging information in debugfs"
+	default y
+	depends on DEBUG_FS
+	---help---
+	Include block layer debugging information in debugfs. This information
+	is mostly useful for kernel developers, but it doesn't incur any cost
+	at runtime.
+
+	Unless you are building a kernel for a tiny system, you should
+	say Y here.
+
 menu "Partition Types"
 
 source "block/partitions/Kconfig"

block/Makefile

@@ -26,4 +26,4 @@ obj-$(CONFIG_BLK_DEV_INTEGRITY) += bio-integrity.o blk-integrity.o t10-pi.o
 obj-$(CONFIG_BLK_MQ_PCI)	+= blk-mq-pci.o
 obj-$(CONFIG_BLK_DEV_ZONED)	+= blk-zoned.o
 obj-$(CONFIG_BLK_WBT)		+= blk-wbt.o
-obj-$(CONFIG_DEBUG_FS)		+= blk-mq-debugfs.o
+obj-$(CONFIG_BLK_DEBUG_FS)	+= blk-mq-debugfs.o

block/blk-mq.h

@@ -84,7 +84,7 @@ extern void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx);
 /*
  * debugfs helpers
  */
-#ifdef CONFIG_DEBUG_FS
+#ifdef CONFIG_BLK_DEBUG_FS
 void blk_mq_debugfs_init(void);
 int blk_mq_debugfs_register(struct request_queue *q, const char *name);
 void blk_mq_debugfs_unregister(struct request_queue *q);
@@ -95,21 +95,22 @@ static inline void blk_mq_debugfs_init(void)
 {
 }
 
-int blk_mq_debugfs_register(struct request_queue *q, const char *name);
+static inline int blk_mq_debugfs_register(struct request_queue *q,
+					  const char *name)
 {
 	return 0;
 }
 
-void blk_mq_debugfs_unregister(struct request_queue *q)
+static inline void blk_mq_debugfs_unregister(struct request_queue *q)
 {
 }
 
-int blk_mq_debugfs_register_hctxs(struct request_queue *q)
+static inline int blk_mq_debugfs_register_hctxs(struct request_queue *q)
 {
 	return 0;
 }
 
-void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)
+static inline void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)
 {
 }
 #endif