_readdir_unlocked
dp = _readdir_unlocked(dirp, RDU_SKIP);
dp = _readdir_unlocked(dirp, RDU_SKIP);
dp = _readdir_unlocked(dirp, RDU_SKIP | RDU_SHORT);
dp = _readdir_unlocked(dirp, 0);
struct dirent *_readdir_unlocked(DIR *, int);