> bus_dma_segment_t
> bus_dma_map(struct uio *uio, int maxsize, int start, int end, int alignment)

I'm actually wondering about the thing Matt obliquely mentioned (which is
far more important than anything I've been fixated on), that is how would
a network interface use this?  The constraints there are:

(1) No uio structure

(2) You sometimes can't do partial operations, the interface may constrain
    you to deliver the full contents of a packet in a single s/g operation.

Dennis Ferguson