/etc/portage/profile/package.provided

The file can contain a list of packages (one per line) that Portage should assume have been provided. This is useful for porting to non-Linux systems. It is essentially a list that replaces the syntax.

For example, to manage a copy of the 4.0 kernel, Portage can be told that sys-kernel/vanilla-sources-4.0.2 has been installed.

Portage will not attempt to update a package that is listed in file unless another package explicitly requires a version that is newer than what has been listed. Dependencies that are satisfied by entries may cause installed packages satisfying equivalent dependencies to be removed by  actions (see the ACTIONS section of the emerge man page for more information).

Format

 * Comments begin with  (no inline comments).
 * One DEPEND atom per line.
 * Relational operators are not allowed.
 * Must include a version.
 * USE flags can be set in package.use

External resources

 * https://forums.gentoo.org/viewtopic-t-1069622.html — Forum talk about drawbacks of package.provided