[Openib-windows] Windows DMA model

[Jan Bottorff]

> Did you check to see what happens if you make a request 
> larger than 2GB?  Is 2GB the threshold?

It seems like individual I/O requests generally can't be bigger than the
buffer described by an MDL. One of the parameters to
GetScatterGatherList is an MDL. MDL's have a 16-bit size field which I
believe limits the maximum buffer an MDL can describe to just under 64
Mbytes (16,000 pages).

I suppose you could have multiple MDL's, that each describe partial
buffers, and call GetScatterGatherList more than once to build the final
bus address scatter gather list.

- Jan