def verifyintegrity(state):
    """Verifies the integrity of file storage.

        ``state`` is a dict holding state of the verifier process. It can be
        used to communicate data between invocations of multiple storage
        primitives.

        If individual revisions cannot have their revision content resolved,
        the method is expected to set the ``skipread`` key to a set of nodes
        that encountered problems.  If set, the method can also add the node(s)
        to ``safe_renamed`` in order to indicate nodes that may perform the
        rename checks with currently accessible data.

        The method yields objects conforming to the ``iverifyproblem``
        interface.
        """
