ext4: support read-only images

Add a rocompat feature, "readonly" to mark a FS image as read-only.
The feature prevents the kernel and e2fsprogs from changing the image;
the flag can be toggled by tune2fs.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index b7f393df2e4c..7fec2efd8635 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1530,6 +1530,7 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
  * GDT_CSUM bits are mutually exclusive.
  */
 #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM    0x0400
+#define EXT4_FEATURE_RO_COMPAT_READONLY         0x1000
 
 #define EXT4_FEATURE_INCOMPAT_COMPRESSION       0x0001
 #define EXT4_FEATURE_INCOMPAT_FILETYPE          0x0002