Commit 2cb5cc8b authored by Darrick J. Wong's avatar Darrick J. Wong Committed by Theodore Ts'o
Browse files

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: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 04ecddb7

fs/ext4/ext4.h

+1 −0
Original line number Diff line number Diff line
@@ -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

fs/ext4/super.c

+9 −1
Original line number Diff line number Diff line
@@ -2776,6 +2776,12 @@ static int ext4_feature_set_ok(struct super_block *sb, int readonly) 
	if (readonly)

		return 1;



	if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_READONLY)) {

		ext4_msg(sb, KERN_INFO, "filesystem is read-only");

		sb->s_flags |= MS_RDONLY;

		return 1;

	}



	/* Check that feature set is OK for a read-write mount */

	if (EXT4_HAS_RO_COMPAT_FEATURE(sb, ~EXT4_FEATURE_RO_COMPAT_SUPP)) {

		ext4_msg(sb, KERN_ERR, "couldn't mount RDWR because of "
@@ -4929,7 +4935,9 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) 
				ext4_mark_recovery_complete(sb, es);

		} else {

			/* Make sure we can mount this feature set readwrite */

			if (!ext4_feature_set_ok(sb, 0)) {

			if (EXT4_HAS_RO_COMPAT_FEATURE(sb,

					EXT4_FEATURE_RO_COMPAT_READONLY) ||

			    !ext4_feature_set_ok(sb, 0)) {

				err = -EROFS;

				goto restore_opts;

			}