def link(self, oldpath, newpath, dir_fd=None):
        """Create a hard link at new_path, pointing at old_path.

        Args:
            oldpath: An existing link to the target file.
            newpath: The destination path to create a new link at.
            dir_fd: If not `None`, the file descriptor of a directory,
                with `oldpath` being relative to this directory.
                New in Python 3.3.

        Returns:
            The FakeFile object referred to by `oldpath`.

        Raises:
            OSError:  if something already exists at new_path.
            OSError:  if the parent directory doesn't exist.
            OSError:  if on Windows before Python 3.2.
        """
        oldpath = self._path_with_dir_fd(oldpath, self.link, dir_fd)
        self.filesystem.link(oldpath, newpath)