btrfs: add filesystems state details to error messages

When a filesystem goes read-only due to an error, multiple errors tend
to be reported, some of which are knock-on failures. Logging fs_states,
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 A) in ...`
and subsequent messages will contain
`(device loop0: state EA) in ...`

In addition to the error states we can also print other states that are
temporary, like remounting, device replace, or indicate a global state
that may affect functionality.

Now implemented:

E - filesystem error detected
A - transaction aborted
L - log tree errors

M - remounting in progress
R - device replace in progress
C - data checksums not verified (mounted with ignoredatacsums)
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -149,6 +149,8 @@ enum {
 
 	/* Indicates there was an error cleaning up a log tree. */
 	BTRFS_FS_STATE_LOG_CLEANUP_ERROR,
+
+	BTRFS_FS_STATE_COUNT
 };
 
 #define BTRFS_BACKREF_REV_MAX		256

fs/btrfs/super.c

@@ -66,6 +66,52 @@ static struct file_system_type btrfs_root_fs_type;
 
 static int btrfs_remount(struct super_block *sb, int *flags, char *data);
 
+#ifdef CONFIG_PRINTK
+
+#define STATE_STRING_PREFACE	": state "
+#define STATE_STRING_BUF_LEN	(sizeof(STATE_STRING_PREFACE) + BTRFS_FS_STATE_COUNT)
+
+/*
+ * Characters to print to indicate error conditions or uncommon filesystem sate.
+ * RO is not an error.
+ */
+static const char fs_state_chars[] = {
+	[BTRFS_FS_STATE_ERROR]			= 'E',
+	[BTRFS_FS_STATE_REMOUNTING]		= 'M',
+	[BTRFS_FS_STATE_RO]			= 0,
+	[BTRFS_FS_STATE_TRANS_ABORTED]		= 'A',
+	[BTRFS_FS_STATE_DEV_REPLACING]		= 'R',
+	[BTRFS_FS_STATE_DUMMY_FS_INFO]		= 0,
+	[BTRFS_FS_STATE_NO_CSUMS]		= 'C',
+	[BTRFS_FS_STATE_LOG_CLEANUP_ERROR]	= 'L',
+};
+
+static void btrfs_state_to_string(const struct btrfs_fs_info *info, char *buf)
+{
+	unsigned int bit;
+	bool states_printed = false;
+	unsigned long fs_state = READ_ONCE(info->fs_state);
+	char *curr = buf;
+
+	memcpy(curr, STATE_STRING_PREFACE, sizeof(STATE_STRING_PREFACE));
+	curr += sizeof(STATE_STRING_PREFACE) - 1;
+
+	for_each_set_bit(bit, &fs_state, sizeof(fs_state)) {
+		WARN_ON_ONCE(bit >= BTRFS_FS_STATE_COUNT);
+		if ((bit < BTRFS_FS_STATE_COUNT) && fs_state_chars[bit]) {
+			*curr++ = fs_state_chars[bit];
+			states_printed = true;
+		}
+	}
+
+	/* If no states were printed, reset the buffer */
+	if (!states_printed)
+		curr = buf;
+
+	*curr++ = 0;
+}
+#endif
+
 /*
  * Generally the error codes correspond to their respective errors, but there
  * are a few special cases.
@@ -128,6 +174,7 @@ 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[STATE_STRING_BUF_LEN];
 	const char *errstr;
 #endif
 
@@ -140,6 +187,7 @@ 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 +196,12 @@ 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 +288,15 @@ 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[STATE_STRING_BUF_LEN];
+
+			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);