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From: "Duane Griffin" <duaneg@dghda.com>
To: Jan Kara <jack@suse.cz>
Cc: Andreas Dilger <adilger@sun.com>,
	Duane Griffin <duaneg@dghda.com>,
	linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
	Theodore Tso <tytso@mit.edu>,
	sct@redhat.com, akpm@linux-foundation.org
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	[thread overview]
Message-ID: <20080312024246.GB21711@dastardly.plus.com> (raw)
In-Reply-To: <20080311151122.GD6544@atrey.karlin.mff.cuni.cz>

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

  reply	other threads:[~2008-03-12  2:43 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-06  1:59 [RFC, PATCH 0/6] ext3: do not modify data on-disk when mounting " Duane Griffin
     [not found] ` <1204768754-29655-2-git-send-email-duaneg@dghda.com>
2008-03-06  1:59   ` [RFC, PATCH 1/6] jbd: eliminate duplicated code in revocation table init/destroy functions Duane Griffin
     [not found]     ` <1204768754-29655-3-git-send-email-duaneg@dghda.com>
2008-03-06  1:59       ` [RFC, PATCH 2/6] jbd: replace potentially false assertion with if block Duane Griffin
2008-03-08 14:52         ` Christoph Hellwig
     [not found]     ` <1204768754-29655-4-git-send-email-duaneg@dghda.com>
2008-03-06  1:59       ` [RFC, PATCH 3/6] jbd: only create debugfs entries if cache initialisation is successful Duane Griffin
     [not found]     ` <1204768754-29655-5-git-send-email-duaneg@dghda.com>
2008-03-06  1:59       ` [RFC, PATCH 4/6] jbd: refactor nested journal log recovery loop into separate functions Duane Griffin
2008-03-08 14:53         ` Christoph Hellwig
2008-03-08 18:40           ` Duane Griffin
2008-03-11 14:35         ` Jan Kara
2008-03-12  1:02           ` Duane Griffin
2008-03-12 10:50             ` Jan Kara
     [not found]     ` <1204768754-29655-6-git-send-email-duaneg@dghda.com>
2008-03-06  1:59       ` [RFC, PATCH 5/6] jbd: add support for read-only log recovery Duane Griffin
2008-03-11 15:05         ` Jan Kara
2008-03-12  1:40           ` Duane Griffin
2008-03-12 10:51             ` Jan Kara
     [not found]     ` <1204768754-29655-7-git-send-email-duaneg@dghda.com>
2008-03-06  1:59       ` [RFC, PATCH 6/6] ext3: do not write to the disk when mounting a dirty read-only filesystem Duane Griffin
2008-03-06  7:17         ` Andreas Dilger
2008-03-06 11:19           ` Duane Griffin
2008-03-11 15:11           ` Jan Kara
2008-03-12  2:42             ` Duane Griffin [this message]
2008-03-12 10:53               ` Jan Kara
2008-03-06  3:42 ` [RFC, PATCH 0/6] ext3: do not modify data on-disk when mounting " Andrew Morton
2008-03-06 11:20   ` Duane Griffin
2008-03-13  3:22 ` Daniel Phillips
2008-03-13 12:35   ` Duane Griffin

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