filesystems/ext4/checksums.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 ---------
10 structures did not have space to fit a full 32-bit checksum, so only the
11 lower 16 bits are stored. Enabling the 64bit feature increases the data
12 structure size so that full 32-bit checksums can be stored for many data
13 structures. However, existing 32-bit filesystems cannot be extended to
14 enable 64bit mode, at least not without the experimental resize2fs
18 ``tune2fs -O metadata_csum`` against the underlying device. If tune2fs
20 checksum, it will request that you run ``e2fsck -D`` to have the
30 .. list-table::
32    :header-rows: 1
34    * - Metadata
35      - Length
36      - Ingredients
37    * - Superblock
38      - \_\_le32
39      - The entire superblock up to the checksum field. The UUID lives inside
41    * - MMP
42      - \_\_le32
43      - UUID + the entire MMP block up to the checksum field.
44    * - Extended Attributes
45      - \_\_le32
46      - UUID + the entire extended attribute block. The checksum field is set to
48    * - Directory Entries
49      - \_\_le32
50      - UUID + inode number + inode generation + the directory block up to the
52    * - HTREE Nodes
53      - \_\_le32
54      - UUID + inode number + inode generation + all valid extents + HTREE tail.
56    * - Extents
57      - \_\_le32
58      - UUID + inode number + inode generation + the entire extent block up to
60    * - Bitmaps
61      - \_\_le32 or \_\_le16
62      - UUID + the entire bitmap. Checksums are stored in the group descriptor,
63        and truncated if the group descriptor size is 32 bytes (i.e. ^64bit)
64    * - Inodes
65      - \_\_le32
66      - UUID + inode number + inode generation + the entire inode. The checksum
68    * - Group Descriptors
69      - \_\_le16
70      - If metadata\_csum, then UUID + group number + the entire descriptor;