[$] Kernel API specification and validation

The kernel project makes a strong promise to its users: the kernel ABI will
not be changed in ways that break user-space code. The occasional failure
notwithstanding, kernel developers do try to live up to that promise. They
are handicapped by one little problem, though: there is no description of
what the kernel ABI is, and no comprehensive way to test whether a given
change breaks it. The kernel API
specification framework proposed (in its second revision) by Sasha
Levin addresses some of those concerns, but the solution is incomplete and
does not come for free.