From owner-freebsd-arch@FreeBSD.ORG  Mon Oct  6 15:27:43 2003
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id E3D4316A4B3
	for <arch@freebsd.org>; Mon,  6 Oct 2003 15:27:43 -0700 (PDT)
Received: from colossus.systems.pipex.net (colossus.systems.pipex.net
	[62.241.160.73])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 73AB743FEC
	for <arch@freebsd.org>; Mon,  6 Oct 2003 15:27:42 -0700 (PDT)
	(envelope-from mark@thuvia.org)
Received: from dotar.thuvia.org (81-86-228-29.dsl.pipex.com [81.86.228.29])
	by colossus.systems.pipex.net (Postfix) with ESMTP
	id 566CA1600032F; Mon,  6 Oct 2003 23:27:40 +0100 (BST)
Received: from dotar.thuvia.org (localhost [127.0.0.1])
	by dotar.thuvia.org (8.12.9/8.12.9) with ESMTP id h96MRdPA075171;
	Mon, 6 Oct 2003 23:27:39 +0100 (BST)
	(envelope-from mark@dotar.thuvia.org)
Received: (from mark@localhost)
	by dotar.thuvia.org (8.12.9/8.12.9/Submit) id h96MRdUf075168;
	Mon, 6 Oct 2003 23:27:39 +0100 (BST)
	(envelope-from mark)
Message-Id: <200310062227.h96MRdUf075168@dotar.thuvia.org>
From: Mark Valentine <mark@valentine.me.uk>
Date: Mon, 6 Oct 2003 23:27:39 +0000
In-Reply-To: <200310062222.h96MM6MO093683@khavrinen.lcs.mit.edu>
X-Mailer: Mail User's Shell (7.2.6 beta(5) 10/07/98)
To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
cc: arch@freebsd.org
Subject: Re: Alignment of disk-I/O from userland.
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussion related to FreeBSD architecture
	<freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 06 Oct 2003 22:27:44 -0000

> From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
> Date: Mon 6 Oct, 2003
> Subject: Re: Alignment of disk-I/O from userland.

> I think you've got that backwards.  When we had block devices, they
> would provide extra buffering to avoid I/O-size breakage.  Character
> devices, which are all we have now, never made any promises.

My point was that we did have block devices which could make such
promises, and that without them the raw device must offer an equivalent
promise (especially when you consider binary compatibility - a program
opening /dev/da0c was written assuming a block device interface).

		Cheers,

		Mark.

-- 
"Tigers will do ANYTHING for a tuna fish sandwich."
"We're kind of stupid that way."   *munch* *munch*
  -- <http://www.calvinandhobbes.com>