From owner-freebsd-arch@FreeBSD.ORG  Mon Jul 10 20:22:42 2006
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
X-Original-To: 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 3AC8716A4DF;
	Mon, 10 Jul 2006 20:22:42 +0000 (UTC) (envelope-from
	SRS0+82d3cd74a67493595751+1051+infradead.org+hch@pentafluge.srs.infradead.org)
Received: from pentafluge.infradead.org (pentafluge.infradead.org
	[213.146.154.40])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 2D76C43D49;
	Mon, 10 Jul 2006 20:22:40 +0000 (GMT) (envelope-from
	SRS0+82d3cd74a67493595751+1051+infradead.org+hch@pentafluge.srs.infradead.org)
Received: from hch by pentafluge.infradead.org with local (Exim 4.62 #1 (Red
	Hat Linux)) id 1G02Gp-0007pl-5f; Mon, 10 Jul 2006 21:22:19 +0100
Date: Mon, 10 Jul 2006 21:22:19 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Scott Long <scottl@samsco.org>
Message-ID: <20060710202219.GA29786@infradead.org>
References: <20060708152801.GA3671@crodrigues.org> <44AFD7DF.8090002@errno.com>
	<20060708174606.GA29602@infradead.org>
	<44B2A51A.4040103@samsco.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <44B2A51A.4040103@samsco.org>
User-Agent: Mutt/1.4.2.1i
X-SRS-Rewrite: SMTP reverse-path rewritten from <hch@infradead.org> by
	pentafluge.infradead.org See http://www.infradead.org/rpr.html
Cc: freebsd-arch@freebsd.org, freebsd-current@freebsd.org,
	Craig Rodrigues <rodrigc@crodrigues.org>
Subject: Re: [RFC] mount can figure out fstype automatically
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.5
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, 10 Jul 2006 20:22:42 -0000

On Mon, Jul 10, 2006 at 01:06:02PM -0600, Scott Long wrote:
> So in your opinion and experience, what are the pros and cons of 
> maintaining a table of magic numbers?

The feature is imensely useful.  The implementation won't win any
points for a clean design but works very well in practice.  I think
it's definitly better than probing in the kernel because letting a filesystem
driver try to make sense of something that's not it's own format can
lead to all kinds of funnies.  Linux does this (iterating all filesystem
types in kernel) for the special case of the root filesystem where mount(8)
is not available, and it showeds various interesting bugs at least in the
fat driver.