From owner-freebsd-arch@FreeBSD.ORG  Tue Oct  7 09:02:46 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 B542616A4B3
	for <arch@freebsd.org>; Tue,  7 Oct 2003 09:02:46 -0700 (PDT)
Received: from arginine.spc.org (arginine.spc.org [195.206.69.236])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 859E043FA3
	for <arch@freebsd.org>; Tue,  7 Oct 2003 09:02:45 -0700 (PDT)
	(envelope-from bms@spc.org)
Received: from localhost (localhost [127.0.0.1])
	by arginine.spc.org (Postfix) with ESMTP
	id 98C0F65419; Tue,  7 Oct 2003 17:02:44 +0100 (BST)
Received: from arginine.spc.org ([127.0.0.1])
 by localhost (arginine.spc.org [127.0.0.1]) (amavisd-new, port 10024)
 with LMTP id 42769-05-4; Tue,  7 Oct 2003 17:02:44 +0100 (BST)
Received: from saboteur.dek.spc.org (unknown [81.3.72.68])
	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by arginine.spc.org (Postfix) with ESMTP
	id 6C11865292; Tue,  7 Oct 2003 17:02:43 +0100 (BST)
Received: by saboteur.dek.spc.org (Postfix, from userid 1001)
	id C870D47; Tue,  7 Oct 2003 17:02:31 +0100 (BST)
Date: Tue, 7 Oct 2003 17:02:31 +0100
From: Bruce M Simpson <bms@spc.org>
To: Ben Mesander <ben@timing.com>
Message-ID: <20031007160231.GB73063@saboteur.dek.spc.org>
References: <200310061753.28562.sam@errno.com>
	<32324.1065508157@critter.freebsd.dk>
	<16258.56989.685473.900678@piglet.timing.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <16258.56989.685473.900678@piglet.timing.com>
cc: Sam Leffler <sam@errno.com>
cc: Poul-Henning Kamp <phk@phk.freebsd.dk>
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: Tue, 07 Oct 2003 16:02:46 -0000

On Tue, Oct 07, 2003 at 09:41:17AM -0600, Ben Mesander wrote:
> How about a flag for open(2), such as O_DIRECT, which would indicate
> if the fd in question is such a device, and you did not sufficiently
> align, etc. your buffers, then you get an error when you attempt the
> I/O operation.

O_DIRECT is already used to indicate that the application wishes to bypass
the buffer cache.

I think Scott's proposal, that the busdma API gets re-used, creating bounce
buffers where necessary, makes sense.

I think that if phk intends to 'raise the bar', he'd better be buying the
drinks at EuroBSDCon. :-)

BMS