Manifest
Generating the Manifest file
In the tree, every package has a Manifest file. This file lives
in the same directory as the ebuilds for the package. The Manifest file
contains digests (the current list can be found in metadata/layout.conf
as manifest-hashes) and file size data for every distfile used
by the package. This is used to verify integrity upon fetching them.
To generate the Manifest, use ebuild foo.ebuild manifest or
pkgdev manifest -m. You may want to set GENTOO_MIRRORS= while
calling it to fetch distfiles from their original locations immediately.
Thin and thick Manifests
There are two kinds of Manifest files in Gentoo: thin Manifests that are used in the development repositories, and thick Manifests that are distributed via rsync to end users. Thin Manifests are described above.
Thick Manifests add checksums for all files in the repository, and an OpenPGP signature. This provides both for integrity and authenticity checking when the repository is transmitted over insecure channels. Thick Manifests are automatically generated on Gentoo Infrastructure, and require no specific action from developers.
Updating Manifest files
Updating existing entries within a manifest must be done with care. Upstream changing the tarball in-place without a new filename could be an innocent respin of the tarball, or it could indicate either the previous or the new tarball is malicious.
Developers should diff the old and new versions of the distfile, comparing
the two, and note the differences in the commit message updating the
Manifest to indicate both what happened (if any context is known) and
also what differences between the two distfiles have been ascertained.
Please note that if upstream made any changes affecting the built
package or it had substantial differences, you need to also bump the ebuild's
revision. Finally, remember to remove the ebuilds that are associated with the
old distfile, or regenerate their checksums in Manifest, if there
are any. This is necessary because these ebuilds will cause checksum
mismatch errors as the checksum recorded in the manifest file no
longer matches the computed checksum of the fetched distfile.
Special care is also required with regard to mirrors.