code: def link(self, oldpath, newpath, dir_fd=None):
          
          oldpath = self._path_with_dir_fd(oldpath, self.link, dir_fd)
          self.filesystem.link(oldpath, newpath)
docs: 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.