From owner-freebsd-current  Thu Feb 12 07:18:26 1998
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id HAA08645
          for current-outgoing; Thu, 12 Feb 1998 07:18:26 -0800 (PST)
          (envelope-from owner-freebsd-current@FreeBSD.ORG)
Received: from ns1.yes.no (ns1.yes.no [195.119.24.10])
          by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id HAA08637
          for <current@FreeBSD.ORG>; Thu, 12 Feb 1998 07:18:18 -0800 (PST)
          (envelope-from eivind@bitbox.follo.net)
Received: from bitbox.follo.net (bitbox.follo.net [194.198.43.36])
	by ns1.yes.no (8.8.7/8.8.7) with ESMTP id PAA15581;
	Thu, 12 Feb 1998 15:18:15 GMT
Received: (from eivind@localhost)
	by bitbox.follo.net (8.8.6/8.8.6) id QAA22660;
	Thu, 12 Feb 1998 16:18:14 +0100 (MET)
Message-ID: <19980212161814.38690@follo.net>
Date: Thu, 12 Feb 1998 16:18:14 +0100
From: Eivind Eklund <eivind@yes.no>
To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>,
        Eivind Eklund <eivind@yes.no>
Cc: current@FreeBSD.ORG
Subject: Re: Heads up: static -ification
References: <19980210030906.20113@follo.net> <199802100857.BAA22938@usr05.primenet.com> <19980212143844.44164@follo.net> <199802121509.KAA21386@khavrinen.lcs.mit.edu>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Mailer: Mutt 0.89.1i
In-Reply-To: <199802121509.KAA21386@khavrinen.lcs.mit.edu>; from Garrett Wollman on Thu, Feb 12, 1998 at 10:09:30AM -0500
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

On Thu, Feb 12, 1998 at 10:09:30AM -0500, Garrett Wollman wrote:
> <<On Thu, 12 Feb 1998 14:38:44 +0100, Eivind Eklund <eivind@yes.no> said:
> 
> > I actually dislike the use of calls between layers at all (or at
> > least in almost all cases).  Layers should communicate through
> > asynchronous messages; that way, you avoid a lot of stupid implict
> > ordering assumptions.
> 
> ``Layering is a great model for designing protocols, but an incredibly
> lousy way of implementing them.''
> 	- D. D. Clark

That quote is often true for protocols, yes.  OTOH, I haven't yet
found a way of implementing advanced protocols that isn't lousy.  And
one of the problems with most layered protocol implementations is that
they don't take the layering far enough - they throw in a lot of
indirect calls and non-visible state as their 'layers', instead of
abstracting enough and consider each layer a process.

At least for operating systems, message-passing systems tend to be
beautifully simple.  The main problem is that if you do them in a
memory-protected environment your performance tend to suck.

Eivind.

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe current" in the body of the message