Am I correct that there is no call like "machine_ptob()" that can be used
by MI device drivers that want to map memory that is on an expansion card
(i.e. PCI) into user space?
  I see that, for instance, the mmap() code for the VGA drivers is all MD.

  For the moment, I'm cheating and using i386_ptob().

  Second, due to lack of actual hardware, I'm simulating part of my card's
memory with system ram. Is there something I should call other than than
malloc() to get memory that is safe for mmap()'ing?

  Or should I really switch to using the bus_dma stuff? It isn't clear to me
how to do this although Jason's paper helped a lot...

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