From: =?utf-8?B?SsO2cm4=?= Engel Subject: Re: Add a norecovery option to ext3/4? Date: Tue, 10 Apr 2007 09:22:53 +0200 Message-ID: <20070410072253.GA28665@lazybastard.org> References: <20070409000556.GA13980@implementation> <461A5F13.7040705@cfl.rr.com> <461A760B.1040103@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Phillip Susi , Samuel Thibault , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Eric Sandeen Return-path: Received: from lazybastard.de ([212.112.238.170]:48121 "EHLO longford.lazybastard.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751911AbXDJH0t (ORCPT ); Tue, 10 Apr 2007 03:26:49 -0400 Content-Disposition: inline In-Reply-To: <461A760B.1040103@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, 9 April 2007 12:21:15 -0500, Eric Sandeen wrote: > Phillip Susi wrote: > >=20 > > When the filesystem is told to mount the disk read only, that means= it=20 > > should not write to it. =20 >=20 > It means the filesystem should not be writeable when it is mounted. > This is not the same as saying that the filesystem itself should do n= o > IO in the course of making that read-only mount available. The filesystem has two interfaces. One to the device underneith, one t= o userspace. Read-only should certainly mean that no writes cross the userspace interface. Traditionally it has implicitly also meant that no writes are crossing the device interface. Whether that was/is an explicit requirement - who knows. Journaling filesystems have introduced this thing called "journal replay". And I have to admit, it makes thing _a lot_ easier to always replay the journal, even when being mounted read-only. But "it is easier" is a pretty lame excuse. > Under all conditions it should be safe to mount a read-only block > device, but that is not the same as mounting a filesystem read-only. In particular, it is a lame excuse when this claim is true. If the block-device is read-only, then journal replay will not work as expecte= d and all the "not so easy" work has to be done anyway. Did I miss anything? Is it actually easier to mount a read-only device with unclean journal than mounting a read-write device and not replay the journal? J=C3=B6rn --=20 Joern's library part 8: http://citeseer.ist.psu.edu/plank97tutorial.html