def fso_mkdir(self, path, mode=None):
path = self.deref(path, to_parent=True)<EOL>if self._lexists(path):<EOL><INDENT>raise OSError(<NUM_LIT>, '<STR_LIT>', path)<EOL><DEDENT>self._addentry(OverlayEntry(self, path, stat.S_IFDIR))<EOL>
overlays os.mkdir()