Some of them turned out to be hyper-corrective duds, like readdir_r. No need for that one, since the buffer it needs can be allocated in the DIR object. You'd never want multiple threads concurrently doing readdir_r from the same DIR stream; there is no credible use case for it. (Or, maybe, optimization? Since it can store the dirent-s directly into some space designated by the caller, eliminating a copy operation from a program that wants to retain all those dirent-s.)