memory-mapped I/O (was: Re: Removing ARCNET stuffs)

[David Holland <dholland-tech%netbsd.org@localhost>]

On Mon, Jun 01, 2015 at 02:23:15PM -0700, Greg A. Woods wrote:
 > That reminds me though.... I've had some ideas of how one might
 > implement stdio solely using memory mapped I/O (which I was thinking of
 > more for the purpose of how one might support POSIX on a Multics-like
 > system, but perhaps it has advantages for a Unix-y system with memmap).

People who are working on nvram storage (phase-change memory,
memristors, stuff like that) will like this, as they have pretty much
taken it as an article of faith that all I/O needs to be memory-mapped
to avoid all the horrible overhead of going through the kernel for
data transfer.

 > Of course if one were actually implementing for a virtual memory based
 > system like Multics then one would not use silly old stdio and other
 > file stream abstractions -- there's just no point to contort all one's
 > algorithms into that corset of an abstraction.

We've had mmap in Unix for going on 30 years, and it remains a poor
second cousin. At least for writing. Coincidence? You decide.

-- 
David A. Holland
dholland%netbsd.org@localhost