[$] Replacement of deprecated kernel APIs

The kernel community tries to never change the user-space API in ways that
will break applications, but it explicitly allows any internal API to be
changed at any time if a solid technical reason to do so exists. But that
doesn't mean that such changes are easy to do. At the 2018 Kernel
Maintainers Summit, Kees Cook led a discussion on the challenges he has
encountered when trying to effect large-scale API changes and what might be
done to make such changes go more smoothly.