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From: jerry@oliveb.UUCP (Jerry Aguirre)
Newsgroups: net.arch,net.micro.16k,net.micro.68k
Subject: Re: Re: 24 bit vs. 32 bit address space
Message-ID: <396@oliveb.UUCP>
Date: Wed, 8-May-85 17:58:37 EDT
Article-I.D.: oliveb.396
Posted: Wed May  8 17:58:37 1985
Date-Received: Fri, 17-May-85 01:16:55 EDT
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Organization: Olivetti ATC; Cupertino, Ca
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> a completely sequential way.  Besides, how does the receiving process know
> when the next lump of data has been deposited at the end of the segment?
> Spin in a loop waiting for the off-the-end-of-the-segment addressing faults
> to stop?  You end up with a substantial amount of specialized machinery
> that is relevant *only* to pipes, defeating the crucial notion that pipes
> "look like" normal files and programs don't need special preparations
> to work from a pipe.
> 				Henry Spencer @ U of Toronto Zoology
> 				{allegra,ihnp4,linus,decvax}!utzoo!henry

Suspending a process on an address fault is the esence of demand paging.
Whether the suspension is for a disk read or a memory write by another
process doesn't change things.  Assuming the hardware allows the
segment to grow, the process can be suspended waiting for a write on the
segment.

Sorry, a pipe does NOT look like a normal file.  Try doing a seek on a
pipe!  If "normal" files were memory mapped then a memory mapped pipe
would look like a "normal" file.  Admittedly this does not give the
equivalent infinite capacity of a pipe but some way of disgarding the
begining of the pipe as the end grows could be thought up.

Perhaps the problem with mapping a tty line into memory is that we are
looking at the wrong level.  Lots of systems have memory mapped
terminals.  A specific character in memory maps to a specific row and
column on the screen.  Software to trap writes to "screen memory" and
provide an optimized screen update (ala curses) would allow driving
remote terminals.

				Jerry Aguirre @ Olivetti ATC
{hplabs|fortune|idi|ihnp4|tolerant|allegra|tymix}!oliveb!jerry