[PATCH v2] btrfs: add fs state details to error messages.

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

When a filesystem goes read-only due to an error, multiple errors tend
to be reported, some of which are knock-on failures. Logging some
fs_states, if any, in btrfs_handle_fs_error() and btrfs_printk()
helps distinguish the first error from subsequent messages which may
only exist due to an error state.

Under the new format, most initial errors will look like:
`BTRFS: error (device loop0) in ...`
while subsequent errors will begin with:
`error (device loop0: state E) in ...`

An initial transaction abort error will look like
`error (device loop0: state X) in ...`
and subsequent messages will contain
`(device loop0: state EX) in ...`

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
v2:
  - Changed btrfs_state_to_string() for clarity
  - Removed superfluous whitespace change

v1:
  - https://lore.kernel.org/linux-btrfs/20220212191042.94954-1-sweettea-kernel@dorminy.me/

 fs/btrfs/super.c | 53 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 4d947ba32da9..42429d68950d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -66,6 +66,37 @@ static struct file_system_type btrfs_root_fs_type;
 
 static int btrfs_remount(struct super_block *sb, int *flags, char *data);
 
+#define STATE_STRING_PREFACE ": state "
+#define MAX_STATE_CHARS 2
+
+static void btrfs_state_to_string(const struct btrfs_fs_info *info, char *buf)
+{
+	unsigned int states_printed = 0;
+	char *curr = buf;
+
+	memcpy(curr, STATE_STRING_PREFACE, sizeof(STATE_STRING_PREFACE));
+	curr += sizeof(STATE_STRING_PREFACE) - 1;
+
+	/* If more states are reported, update MAX_STATE_CHARS also */
+	if (test_bit(BTRFS_FS_STATE_ERROR, &info->fs_state)) {
+		*curr++ = 'E';
+		states_printed++;
+	}
+
+	if (test_bit(BTRFS_FS_STATE_TRANS_ABORTED, &info->fs_state)) {
+		*curr++ = 'X';
+		states_printed++;
+	}
+
+	/* If no states were printed, reset the buffer */
+	if (!states_printed)
+		curr = buf;
+
+	WARN_ON_ONCE(states_printed > MAX_STATE_CHARS);
+
+	*curr++ = '\0';
+}
+
 /*
  * Generally the error codes correspond to their respective errors, but there
  * are a few special cases.
@@ -128,6 +159,7 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
 {
 	struct super_block *sb = fs_info->sb;
 #ifdef CONFIG_PRINTK
+	char statestr[sizeof(STATE_STRING_PREFACE) + MAX_STATE_CHARS];
 	const char *errstr;
 #endif
 
@@ -140,6 +172,7 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
 
 #ifdef CONFIG_PRINTK
 	errstr = btrfs_decode_error(errno);
+	btrfs_state_to_string(fs_info, statestr);
 	if (fmt) {
 		struct va_format vaf;
 		va_list args;
@@ -148,12 +181,12 @@ void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function
 		vaf.fmt = fmt;
 		vaf.va = &args;
 
-		pr_crit("BTRFS: error (device %s) in %s:%d: errno=%d %s (%pV)\n",
-			sb->s_id, function, line, errno, errstr, &vaf);
+		pr_crit("BTRFS: error (device %s%s) in %s:%d: errno=%d %s (%pV)\n",
+			sb->s_id, statestr, function, line, errno, errstr, &vaf);
 		va_end(args);
 	} else {
-		pr_crit("BTRFS: error (device %s) in %s:%d: errno=%d %s\n",
-			sb->s_id, function, line, errno, errstr);
+		pr_crit("BTRFS: error (device %s%s) in %s:%d: errno=%d %s\n",
+			sb->s_id, statestr, function, line, errno, errstr);
 	}
 #endif
 
@@ -240,11 +273,15 @@ void __cold btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, .
 	vaf.va = &args;
 
 	if (__ratelimit(ratelimit)) {
-		if (fs_info)
-			printk("%sBTRFS %s (device %s): %pV\n", lvl, type,
-				fs_info->sb->s_id, &vaf);
-		else
+		if (fs_info) {
+			char statestr[sizeof(STATE_STRING_PREFACE) + MAX_STATE_CHARS];
+
+			btrfs_state_to_string(fs_info, statestr);
+			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);
+		}
 	}
 
 	va_end(args);
-- 
2.35.1