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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.arch
Subject: Re: inside the OS vs. outside the OS
Message-ID: <5329@utzoo.UUCP>
Date: Sat, 23-Mar-85 19:55:43 EST
Article-I.D.: utzoo.5329
Posted: Sat Mar 23 19:55:43 1985
Date-Received: Sat, 23-Mar-85 19:55:43 EST
References: <501@harvard.ARPA>
Organization: U of Toronto Zoology
Lines: 25

> Shouldn't the kernel part of a terminal driver be just two ring buffers,
> one for input characters and one for output? The driver should just fill
> and empty these buffers.
> 
> Then the user can link in whatever routines are necessary for the
> particular application to do all of the rest. When I'm using a screen
> text editor that turns off echo and puts the terminal in RAW mode, why
> do I have to pay for the checks for echo and flow control and all of the
> rest.

Because if it isn't done in a central place, history shows that programmers
don't bother providing it at all.  Look at the wild chaos of different
keyboard conventions in the old Xerox Alto software.  Unix originally did
not provide centralized "fancy" tty handling, and as a result one could
seldom count on even something as simple as a backspace character.  This
got fixed long ago, fortunately.

Mind you, I agree that much of that machinery shouldn't be imbedded down
in the kernel, where it's very hard to fix problems with it.  The trick
is to move it out of the kernel while retaining the centralization, so
that change is easy (and can be done on an individual basis) but all
programs still get the full functionality by default.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry