From: "Duane Griffin" Subject: Re: [RFC, PATCH 6/6] ext3: do not write to the disk when mounting a dirty read-only filesystem Date: Wed, 12 Mar 2008 02:42:46 +0000 Message-ID: <20080312024246.GB21711@dastardly.plus.com> References: <20080306071734.GN3616@webber.adilger.int> <20080311151122.GD6544@atrey.karlin.mff.cuni.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , Duane Griffin , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Theodore Tso , sct@redhat.com, akpm@linux-foundation.org To: Jan Kara Return-path: Received: from kumera.dghda.com ([80.68.90.171]:4770 "EHLO kumera.dghda.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750992AbYCLCmt (ORCPT ); Tue, 11 Mar 2008 22:42:49 -0400 Content-Disposition: inline In-Reply-To: <20080311151122.GD6544@atrey.karlin.mff.cuni.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Mar 11, 2008 at 04:11:23PM +0100, Jan Kara wrote: > Actually, this is nastier than it looks - currently fs, asks > ext3_sb_getblk() for block 'a' and it gets buffer head with b_blocknr == 'b' > instead. Note that it will be a different device as well, in the case of an external journal. > So when remounting you'd have to rewrite these buffers with > original block numbers which is not really possible. So I think > remapping will have to be solved differently, like providing buffer > head with correct b_blocknr but taking care when reading data to it and > reading them from elsewhere. Actually, this has to be done anyway > because JBD escapes data in the journal and you have to do unescaping > when reading data... Hmm, I'll think about this and try to get something working. As a quick proof-of-concept hack, getting both buffers then overwriting the fs block's data with the unescaped journal data should do the trick, right? Cheers, Duane. -- "I never could learn to drink that blood and call it wine" - Bob Dylan