ext4: documentation fixes

This commit aims to fix the following issues in ext4 documentation:
- Flexible block group docs said that the aim was to group block
  metadata together instead of block group metadata.
- The documentation consistly uses "location" instead of "block number".
  It is easy to confuse location to be an absolute offset on disk. Added
  a line to clarify all location values are in terms of block numbers.
- Dirent2 docs said that the rec_len field is shortened instead of the
  name_len field.
- Typo in bg_checksum description.
- Inode size is 160 bytes now, and hence i_extra_isize is now 32.
- Cluster size formula was incorrect, it did not include the +10 to
  s_log_cluster_size value.
- Typo: there were two s_wtime_hi in the superblock struct.
- Superblock struct was outdated, added the new fields which were part
  of s_reserved earlier.
- Multiple mount protection seems to be implemented in fs/ext4/mmp.c.

Signed-off-by: Ayush Ranjan <ayushr2@illinois.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>

1 files changed, 14 insertions, 6 deletions

diff --git a/Documentation/filesystems/ext4/super.rst b/Documentation/filesystems/ext4/super.rst
index 04ff079a2acf..48b6c78fc38e 100644
--- a/Documentation/filesystems/ext4/super.rst
+++ b/Documentation/filesystems/ext4/super.rst
@@ -58,7 +58,7 @@ The ext4 superblock is laid out as follows in
    * - 0x1C
      - \_\_le32
      - s\_log\_cluster\_size
-     - Cluster size is (2 ^ s\_log\_cluster\_size) blocks if bigalloc is
+     - Cluster size is 2 ^ (10 + s\_log\_cluster\_size) blocks if bigalloc is
        enabled. Otherwise s\_log\_cluster\_size must equal s\_log\_block\_size.
    * - 0x20
      - \_\_le32
@@ -447,7 +447,7 @@ The ext4 superblock is laid out as follows in
      - Upper 8 bits of the s_wtime field.
    * - 0x275
      - \_\_u8
-     - s\_wtime_hi
+     - s\_mtime_hi
      - Upper 8 bits of the s_mtime field.
    * - 0x276
      - \_\_u8
@@ -466,12 +466,20 @@ The ext4 superblock is laid out as follows in
      - s\_last_error_time_hi
      - Upper 8 bits of the s_last_error_time_hi field.
    * - 0x27A
-     - \_\_u8[2]
-     - s\_pad
+     - \_\_u8
+     - s\_pad[2]
      - Zero padding.
    * - 0x27C
+     - \_\_le16
+     - s\_encoding
+     - Filename charset encoding.
+   * - 0x27E
+     - \_\_le16
+     - s\_encoding_flags
+     - Filename charset encoding flags.
+   * - 0x280
      - \_\_le32
-     - s\_reserved[96]
+     - s\_reserved[95]
      - Padding to the end of the block.
    * - 0x3FC
      - \_\_le32
@@ -617,7 +625,7 @@ following:
    * - 0x80
      - Enable a filesystem size of 2^64 blocks (INCOMPAT\_64BIT).
    * - 0x100
-     - Multiple mount protection. Not implemented (INCOMPAT\_MMP).
+     - Multiple mount protection (INCOMPAT\_MMP).
    * - 0x200
      - Flexible block groups. See the earlier discussion of this feature
        (INCOMPAT\_FLEX\_BG).