def virtualchain_set_opfields( op, **fields ):
    """
    Pass along virtualchain-reserved fields to a virtualchain operation.
    This layer of indirection is meant to help with future compatibility,
    so virtualchain implementations do not try to set operation fields
    directly.
    """

    # warn about unsupported fields
    for f in fields.keys():
        if f not in indexer.RESERVED_KEYS:
            log.warning("Unsupported virtualchain field '%s'" % f)

    # propagate reserved fields
    for f in fields.keys():
        if f in indexer.RESERVED_KEYS:
            op[f] = fields[f]

    return op
Pass along virtualchain-reserved fields to a virtualchain operation.
    This layer of indirection is meant to help with future compatibility,
    so virtualchain implementations do not try to set operation fields
    directly.