[PATCH v2] Add FAT messages to printk index

[Jonathan Lassoff <jof@thejof.com>]

In order for end users to quickly react to new issues that come up in
production, it is proving useful to leverage the printk indexing system. This
printk index enables kernel developers to use calls to printk() with changable
ad-hoc format strings, while still enabling end users to detect changes and
develop a semi-stable interface for detecting and parsing these messages.

So that detailed FAT messages are captured by this printk index, this patch
wraps fat_msg with a macro.

PATCH v1 -- Fix indentation with tabs in fat_msg macro
PATCH v2 -- Define FAT_PRINTK_PREFIX
PATCH v3 -- Fix kernel-doc comment for _fat_msg()

Reported-by: kernel test robot <lkp@intel.com>
---
 fs/fat/fat.h  |  9 ++++++++-
 fs/fat/misc.c | 14 ++++++++++----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 02d4d4234956..2a20a21f2fb9 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -433,8 +433,15 @@ void __fat_fs_error(struct super_block *sb, int report, const char *fmt, ...);
 	__fat_fs_error(sb, 1, fmt , ## args)
 #define fat_fs_error_ratelimit(sb, fmt, args...) \
 	__fat_fs_error(sb, __ratelimit(&MSDOS_SB(sb)->ratelimit), fmt , ## args)
+
+#define FAT_PRINTK_PREFIX "%sFAT-fs (%s): "
+#define fat_msg(sb, level, fmt, args...)				\
+do {									\
+	printk_index_subsys_emit(FAT_PRINTK_PREFIX, level, fmt, ##args);\
+	_fat_msg(sb, level, fmt, ##args);				\
+} while(0)
 __printf(3, 4) __cold
-void fat_msg(struct super_block *sb, const char *level, const char *fmt, ...);
+void _fat_msg(struct super_block *sb, const char *level, const char *fmt, ...);
 #define fat_msg_ratelimit(sb, level, fmt, args...)	\
 	do {	\
 			if (__ratelimit(&MSDOS_SB(sb)->ratelimit))	\
diff --git a/fs/fat/misc.c b/fs/fat/misc.c
index 91ca3c304211..855477d89f41 100644
--- a/fs/fat/misc.c
+++ b/fs/fat/misc.c
@@ -42,10 +42,16 @@ void __fat_fs_error(struct super_block *sb, int report, const char *fmt, ...)
 EXPORT_SYMBOL_GPL(__fat_fs_error);
 
 /**
- * fat_msg() - print preformated FAT specific messages. Every thing what is
- * not fat_fs_error() should be fat_msg().
+ * _fat_msg() - Print a preformatted FAT message based on a superblock.
+ * @sb: A pointer to a &struct super_block
+ * @level: A Kernel printk level constant
+ * @fmt: The printf-style format string to print.
+ *
+ * Everything that is not fat_fs_error() should be fat_msg().
+ *
+ * fat_msg() wraps _fat_msg() for printk indexing.
  */
-void fat_msg(struct super_block *sb, const char *level, const char *fmt, ...)
+void _fat_msg(struct super_block *sb, const char *level, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -53,7 +59,7 @@ void fat_msg(struct super_block *sb, const char *level, const char *fmt, ...)
 	va_start(args, fmt);
 	vaf.fmt = fmt;
 	vaf.va = &args;
-	printk("%sFAT-fs (%s): %pV\n", level, sb->s_id, &vaf);
+	_printk(FAT_PRINTK_PREFIX "%pV\n", level, sb->s_id, &vaf);
 	va_end(args);
 }
 
-- 
2.30.2