[Openib-windows] Windows DMA model

[Fab Tillier]

> From: Jan Bottorff [mailto:jbottorff at xsigo.com]
> Sent: Tuesday, January 17, 2006 5:51 PM
> 
> > 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.

GetScatterGatherList will handle chained MDLs as long as there are enough map
registers available, so a single call should suffice.  The MDLs have a Next
member to allow them to be chained.

- Fab