[PATCH 2/7] ext4: add EXT4_FLAGS_EMERGENCY_RO bit

[libaokun]

From: Baokun Li <libaokun1@xxxxxxxxxx>

EXT4_FLAGS_EMERGENCY_RO Indicates that the current file system has become
read-only due to some error. Compared to SB_RDONLY, setting it does not
require a lock because we won't clear it, which avoids over-coupling with
vfs freeze. Also, add a helper function ext4_emergency_ro() to check if
the bit is set.

Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
 fs/ext4/ext4.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 612208527512..c5b775482897 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2235,7 +2235,8 @@ extern int ext4_feature_set_ok(struct super_block *sb, int readonly);
 enum {
 	EXT4_FLAGS_RESIZING,	/* Avoid superblock update and resize race */
 	EXT4_FLAGS_SHUTDOWN,	/* Prevent access to the file system */
-	EXT4_FLAGS_BDEV_IS_DAX	/* Current block device support DAX */
+	EXT4_FLAGS_BDEV_IS_DAX,	/* Current block device support DAX */
+	EXT4_FLAGS_EMERGENCY_RO	/* Emergency read-only due to fs errors */
 };
 
 static inline int ext4_forced_shutdown(struct super_block *sb)
@@ -2243,6 +2244,11 @@ static inline int ext4_forced_shutdown(struct super_block *sb)
 	return test_bit(EXT4_FLAGS_SHUTDOWN, &EXT4_SB(sb)->s_ext4_flags);
 }
 
+static inline int ext4_emergency_ro(struct super_block *sb)
+{
+	return test_bit(EXT4_FLAGS_EMERGENCY_RO, &EXT4_SB(sb)->s_ext4_flags);
+}
+
 /*
  * Default values for user and/or group using reserved blocks
  */
-- 
2.39.2