xdr_set_page_base
if (xdr_set_page_base(xdr, base, len) == 0) {
xdr_set_page_base(xdr, newbase, xdr_stream_remaining(xdr));
xdr_set_page_base(xdr, 0, buf->len) == 0)
xdr_set_page_base(xdr, 0, len);