This option enables fs-verity. fs-verity is the dm-verity
mechanism implemented at the file level. On supported
filesystems (currently ext4, f2fs, and btrfs), userspace can
use an ioctl to enable verity for a file, which causes the
filesystem to build a Merkle tree for the file. The filesystem
will then transparently verify any data read from the file
against the Merkle tree. The file is also made read-only.

This serves as an integrity check, but the availability of the
Merkle tree root hash also allows efficiently supporting
various use cases where normally the whole file would need to
be hashed at once, such as: (a) auditing (logging the file's
hash), or (b) authenticity verification (comparing the hash
against a known good value, e.g. from a digital signature).

fs-verity is especially useful on large files where not all
the contents may actually be needed. Also, fs-verity verifies
data each time it is paged back in, which provides better
protection against malicious disks vs. an ahead-of-time hash.

If unsure, say N.

source code:

fs/verity/