See https://docs.google.com/document/d/1C5b81g0W6th5Ti5P6nlWrjc2qsR8I6sTFuy0bYum OfI/edit?usp=sharing I have now coded up and tested both wrap and unwrap. The exercise resulted in some refinement of the interface of the new functions. It turns out that x_iovcount and x_fillbufs with minor tweaks are useful in the unwrap side also. Code to follow soon. Frank