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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>
This commit is contained in:
Darrick J. Wong 2015-02-12 22:31:21 -05:00 committed by Theodore Ts'o
parent 04ecddb73d
commit 2cb5cc8b09
2 changed files with 10 additions and 1 deletions
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1
fs/ext4/ext4.h
View File

@ -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

10
fs/ext4/super.c
View File

@ -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;
}