support-read-only-images

   1 ext4: support read-only images
   2
   3 From: "Darrick J. Wong" <darrick.wong@oracle.com>
   4
   5 Add a rocompat feature, "readonly" to mark a FS image as read-only.
   6 The feature prevents the kernel and e2fsprogs from changing the image;
   7 the flag can be toggled by tune2fs.
   8
   9 Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  10 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  11 ---
  12  fs/ext4/ext4.h  |    1 +
  13  fs/ext4/super.c |   10 +++++++++-
  14  2 files changed, 10 insertions(+), 1 deletion(-)
  15
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  20
  21 diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
  22 index 3950a2f..5cf937d 100644
  23 --- a/fs/ext4/ext4.h
  24 +++ b/fs/ext4/ext4.h
  25 @@ -1557,6 +1557,7 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
  26   * GDT_CSUM bits are mutually exclusive.
  27   */
  28  #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM   0x0400
  29 +#define EXT4_FEATURE_RO_COMPAT_READONLY                0x1000
  30
  31  #define EXT4_FEATURE_INCOMPAT_COMPRESSION      0x0001
  32  #define EXT4_FEATURE_INCOMPAT_FILETYPE         0x0002
  33 diff --git a/fs/ext4/super.c b/fs/ext4/super.c
  34 index 74c5f53..c65dede 100644
  35 --- a/fs/ext4/super.c
  36 +++ b/fs/ext4/super.c
  37 @@ -2776,6 +2776,12 @@ static int ext4_feature_set_ok(struct super_block *sb, int readonly)
  38         if (readonly)
  39                 return 1;
  40
  41 +       if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_READONLY)) {
  42 +               ext4_msg(sb, KERN_INFO, "filesystem is read-only");
  43 +               sb->s_flags |= MS_RDONLY;
  44 +               return 1;
  45 +       }
  46 +
  47         /* Check that feature set is OK for a read-write mount */
  48         if (EXT4_HAS_RO_COMPAT_FEATURE(sb, ~EXT4_FEATURE_RO_COMPAT_SUPP)) {
  49                 ext4_msg(sb, KERN_ERR, "couldn't mount RDWR because of "
  50 @@ -4930,7 +4936,9 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
  51                                 ext4_mark_recovery_complete(sb, es);
  52                 } else {
  53                         /* Make sure we can mount this feature set readwrite */
  54 -                       if (!ext4_feature_set_ok(sb, 0)) {
  55 +                       if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
  56 +                                       EXT4_FEATURE_RO_COMPAT_READONLY) ||
  57 +                           !ext4_feature_set_ok(sb, 0)) {
  58                                 err = -EROFS;
  59                                 goto restore_opts;
  60                         }