From owner-svn-src-all@FreeBSD.ORG Tue Sep 29 20:13:20 2009 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A4F51106566C; Tue, 29 Sep 2009 20:13:20 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from harmony.bsdimp.com (bsdimp.com [199.45.160.85]) by mx1.freebsd.org (Postfix) with ESMTP id 60A328FC16; Tue, 29 Sep 2009 20:13:20 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by harmony.bsdimp.com (8.14.3/8.14.1) with ESMTP id n8TKAs3D039060; Tue, 29 Sep 2009 14:10:54 -0600 (MDT) (envelope-from imp@bsdimp.com) Date: Tue, 29 Sep 2009 14:12:56 -0600 (MDT) Message-Id: <20090929.141256.-981704958.imp@bsdimp.com> To: xcllnt@mac.com From: "M. Warner Losh" In-Reply-To: References: <1F22EA6A-2793-45CE-9669-3FFD550CF4E2@mac.com> X-Mailer: Mew version 5.2 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: marcel@freebsd.org, jhb@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, rwatson@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r197608 - head/sys/geom/part X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 29 Sep 2009 20:13:20 -0000 In message: Marcel Moolenaar writes: : : On Sep 29, 2009, at 10:00 AM, Robert Watson wrote: : : > : > On Tue, 29 Sep 2009, Marcel Moolenaar wrote: : > : >>> Why do you check for zeros at all? AFAIK, the only real check is : >>> for AA55 at the end of the sector (and having an MBR or other : >>> Extended MBR partition entry point at the sector in question). : >>> The '96' thing seems rather arbitrary in the code, and I think the : >>> zero's check is overly restrictive. : >> : >> Only checking for a signature that 99% of the boot blocks have : >> isn't enough. The msdos file system has that signature and the : >> check for all-zeroes is to prevent false positives there. : > : > And, as I recall, the msdosfs check has been gradually getting : > weaker over time as the constraints it places on things like : > cylinder counts become obsolete. It's not quite that we'll mount : > msdosfs on any random pile of bytes, but it might be getting there... : : We really need to get to a point where we treat partition types : seriously and : use it to help avoid false positives. Reducing or eliminating false : positives : is critical if we ever want to go towards DWIM or auto-mounting. With : the : partition type taken into consideration, we may be able to eliminate : ad hoc : checks, like the zero check in g_part_ebr, without creating false : positives. Part of the problem too is that the msdosfs code checks too many things, making it hard to use on raw images :( Of course, I'm about 12 sigma from the mean on the images I use, but still... Warner