Return fullPath relative to Store directory.

        Return fullPath if fullPath is not inside directory.

        Return None if fullPath is outside our scope.

def _relativePath(self, fullPath):
        """ Return fullPath relative to Store directory.

        Return fullPath if fullPath is not inside directory.

        Return None if fullPath is outside our scope.
        """
        if fullPath is None:
            return None

        assert fullPath.startswith("/"), fullPath

        path = os.path.relpath(fullPath, self.userPath)

        if not path.startswith("../"):
            return path
        elif self.ignoreExtraVolumes:
            return None
        else:
            return fullPath