The mode argument can be ignored in OS/161.
ENODEV The device prefix of pathname did not exist. ENOTDIR A non-final component of pathname was not a directory. ENOENT A non-final component of pathname did not exist. EEXIST An object by the name pathname already exists. ENOSPC The filesystem the directory was to be created on is full. EIO A hard I/O error occurred. EFAULT pathname was an invalid pointer.