You only re-export the unchanged parts. EVFILT_AIO is the same in 0.2.0 and 0.2.1 (which is different - in practice and to the compiler - to EVFILT_AIO in 0.3). (Only) c_void is the same in 0.2.0, 0.2.1 and 0.3 (again, in practice and to the compiler.)