btrfs: add 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 this printk indexing
system. This printk index enables kernel developers to use calls to
printk() with changeable 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 Btrfs messages are captured by this printk index, this
patch wraps btrfs_printk and btrfs_handle_fs_error with macros.

Example of the generated list:
https://lore.kernel.org/lkml/12588e13d51a9c3bf59467d3fc1ac2162f1275c1.1647539056.git.jof@thejof.comSigned-off-by: Jonathan Lassoff <jof@thejof.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3451,11 +3451,29 @@ void btrfs_no_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
 }
 
-#ifdef CONFIG_PRINTK
+#ifdef CONFIG_PRINTK_INDEX
+
+#define btrfs_printk(fs_info, fmt, args...)					\
+do {										\
+	printk_index_subsys_emit("%sBTRFS %s (device %s): ", NULL, fmt);	\
+	_btrfs_printk(fs_info, fmt, ##args);					\
+} while (0)
+
+__printf(2, 3)
+__cold
+void _btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...);
+
+#elif defined(CONFIG_PRINTK)
+
+#define btrfs_printk(fs_info, fmt, args...)				\
+	_btrfs_printk(fs_info, fmt, ##args)
+
 __printf(2, 3)
 __cold
-void btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...);
+void _btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...);
+
 #else
+
 #define btrfs_printk(fs_info, fmt, args...) \
 	btrfs_no_printk(fs_info, fmt, ##args)
 #endif
@@ -3706,12 +3724,25 @@ do {								\
 				  __LINE__, (errno));		\
 } while (0)
 
+#ifdef CONFIG_PRINTK_INDEX
+
 #define btrfs_handle_fs_error(fs_info, errno, fmt, args...)		\
-do {								\
-	__btrfs_handle_fs_error((fs_info), __func__, __LINE__,	\
-			  (errno), fmt, ##args);		\
+do {									\
+	printk_index_subsys_emit(					\
+		"BTRFS: error (device %s%s) in %s:%d: errno=%d %s",	\
+		KERN_CRIT, fmt);					\
+	__btrfs_handle_fs_error((fs_info), __func__, __LINE__,		\
+				(errno), fmt, ##args);			\
 } while (0)
 
+#else
+
+#define btrfs_handle_fs_error(fs_info, errno, fmt, args...)		\
+	__btrfs_handle_fs_error((fs_info), __func__, __LINE__,		\
+				(errno), fmt, ##args)
+
+#endif
+
 #define BTRFS_FS_ERROR(fs_info)	(unlikely(test_bit(BTRFS_FS_STATE_ERROR, \
 						   &(fs_info)->fs_state)))
 #define BTRFS_FS_LOG_CLEANUP_ERROR(fs_info)				\

fs/btrfs/super.c

@@ -261,7 +261,7 @@ static struct ratelimit_state printk_limits[] = {
 	RATELIMIT_STATE_INIT(printk_limits[7], DEFAULT_RATELIMIT_INTERVAL, 100),
 };
 
-void __cold btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
+void __cold _btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
 	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
 	struct va_format vaf;
@@ -292,10 +292,10 @@ void __cold btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, .
 			char statestr[STATE_STRING_BUF_LEN];
 
 			btrfs_state_to_string(fs_info, statestr);
-			printk("%sBTRFS %s (device %s%s): %pV\n", lvl, type,
+			_printk("%sBTRFS %s (device %s%s): %pV\n", lvl, type,
 				fs_info->sb->s_id, statestr, &vaf);
 		} else {
-			printk("%sBTRFS %s: %pV\n", lvl, type, &vaf);
+			_printk("%sBTRFS %s: %pV\n", lvl, type, &vaf);
 		}
 	}