[$] Replacement of deprecated kernel APIs

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