From owner-freebsd-fs@freebsd.org Sat Oct 28 22:27:58 2017 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id DFE9AE4F014 for ; Sat, 28 Oct 2017 22:27:58 +0000 (UTC) (envelope-from mckusick@mckusick.com) Received: from chez.mckusick.com (chez.mckusick.com [70.36.157.235]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id C63EF825A0; Sat, 28 Oct 2017 22:27:58 +0000 (UTC) (envelope-from mckusick@mckusick.com) Received: from chez.mckusick.com (localhost [IPv6:::1]) by chez.mckusick.com (8.15.2/8.15.2) with ESMTP id v9SMPDCZ074228; Sat, 28 Oct 2017 15:25:13 -0700 (PDT) (envelope-from mckusick@chez.mckusick.com) Message-Id: <201710282225.v9SMPDCZ074228@chez.mckusick.com> From: Kirk McKusick To: Mark Johnston Subject: Re: softdep as a mount(8) option cc: freebsd-fs@FreeBSD.org In-reply-to: <20171027153859.GC2385@raichu> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <74226.1509229513.1@chez.mckusick.com> Date: Sat, 28 Oct 2017 15:25:13 -0700 X-Spam-Status: No, score=-1.4 required=5.0 tests=BAYES_00,MISSING_MID, UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on chez.mckusick.com X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 28 Oct 2017 22:27:59 -0000 > Date: Fri, 27 Oct 2017 11:39:00 -0400 > From: Mark Johnston > To: freebsd-fs@FreeBSD.org > Subject: softdep as a mount(8) option > > Hi, > > I'd like to finally enable the use of SU (not SU+J) on some small UFS > filesystems. The fact that SU is enabled using a flag in the superblock > poses a problem for me, however: the systems containing these > filesystems may at any time be repurposed to run a kernel that supports > SU but contains bugs[*] that render it unusable. I therefore can't > persistently enable SU in these systems. > > I'm wondering if it would be possible to enable SU using a mount > option rather than with a persistent flag. fsck_ffs conditionalizes some > of its logic on whether SU is configured - is this necessary for > correctness? That is, if I run fsck on an unclean filesystem that had > been mounted with SU, and fsck runs as though SU hadn't been configured, > what problems might arise? > > [*] These bugs are a result of local modifications and aren't in > FreeBSD. While it is safe and possible to add soft-updates (but not journalled soft updates) as a mount option, it means that fsck will not know that soft updates were in use, so it will always run in full (slow) mode at boot time. This is why I have not added it as an option. Kirk McKusick