1.. SPDX-License-Identifier: GPL-2.0
2
3Verity files
4------------
5
6ext4 supports fs-verity, which is a filesystem feature that provides
7Merkle tree based hashing for individual readonly files.  Most of
8fs-verity is common to all filesystems that support it; see
9:ref:`Documentation/filesystems/fsverity.rst <fsverity>` for the
10fs-verity documentation.  However, the on-disk layout of the verity
11metadata is filesystem-specific.  On ext4, the verity metadata is
12stored after the end of the file data itself, in the following format:
13
14- Zero-padding to the next 65536-byte boundary.  This padding need not
15  actually be allocated on-disk, i.e. it may be a hole.
16
17- The Merkle tree, as documented in
18  :ref:`Documentation/filesystems/fsverity.rst
19  <fsverity_merkle_tree>`, with the tree levels stored in order from
20  root to leaf, and the tree blocks within each level stored in their
21  natural order.
22
23- Zero-padding to the next filesystem block boundary.
24
25- The verity descriptor, as documented in
26  :ref:`Documentation/filesystems/fsverity.rst <fsverity_descriptor>`,
27  with optionally appended signature blob.
28
29- Zero-padding to the next offset that is 4 bytes before a filesystem
30  block boundary.
31
32- The size of the verity descriptor in bytes, as a 4-byte little
33  endian integer.
34
35Verity inodes have EXT4_VERITY_FL set, and they must use extents, i.e.
36EXT4_EXTENTS_FL must be set and EXT4_INLINE_DATA_FL must be clear.
37They can have EXT4_ENCRYPT_FL set, in which case the verity metadata
38is encrypted as well as the data itself.
39
40Verity files cannot have blocks allocated past the end of the verity
41metadata.
42
43Verity and DAX are not compatible and attempts to set both of these flags
44on a file will fail.
45