fatfs: add FAT messages to printk index

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
changeable ad-hoc format strings (as they always have; no change of
expectations), while enabling end users to examine format strings to
detect changes.

Since end users are using regular expressions to match messages printed
through printk(), being able to detect changes in chosen format strings
from release to release provides a useful signal to review
printk()-matching regular expressions for any necessary updates.

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

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/8aaa2dd7995e820292bb40d2120ab69756662c65.1648688136.git.jof@thejof.comSigned-off-by: Jonathan Lassoff <jof@thejof.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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))	\

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);
 }