ext4: show 'emergency_ro' when EXT4_FLAGS_EMERGENCY_RO is set

After commit d3476f3 ("ext4: don't set SB_RDONLY after filesystem
errors") in v6.12-rc1, the 'errors=remount-ro' mode no longer sets
SB_RDONLY on errors, which results in us seeing the filesystem is still
in rw state after errors.

Therefore, after setting EXT4_FLAGS_EMERGENCY_RO, display the emergency_ro
option so that users can query whether the current file system has become
emergency read-only due to errors through commands such as 'mount' or
'cat /proc/fs/ext4/sdx/options'.

Fixes: d3476f3 ("ext4: don't set SB_RDONLY after filesystem errors")
Signed-off-by: Baokun Li <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Zhang Yi <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: LiBaokun96

fs/ext4/super.c

@@ -3029,6 +3029,9 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 	if (nodefs && !test_opt(sb, NO_PREFETCH_BLOCK_BITMAPS))
 		SEQ_OPTS_PUTS("prefetch_block_bitmaps");
 
+	if (ext4_emergency_ro(sb))
+		SEQ_OPTS_PUTS("emergency_ro");
+
 	ext4_show_quota_options(seq, sb);
 	return 0;
 }