It's only the first step of the puzzle. And arguably only a half step. As the article points out anytime that off_t is stuffed into a struct, or used in a function call, or integrated into a protocol, the abstraction is lost and the actual size matters. Mixing old and new code, either by loading a library or communicating over a protocol, means you get offsets wrong and things start crashing. Ultimately the changeover requires everybody to segregate their programs between "legacy" and "has been ported or at least looked over", which is incredibly painful.