linux-ext4 - Re: Add a norecovery option to ext3/4?

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Message-ID: <20070410164451.GC10459@waste.org>
Date:	Tue, 10 Apr 2007 11:44:51 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Jörn Engel <joern@...ybastard.org>
Cc:	Theodore Tso <tytso@....edu>, Eric Sandeen <sandeen@...hat.com>,
	Phillip Susi <psusi@....rr.com>,
	Samuel Thibault <samuel.thibault@...-lyon.org>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Add a norecovery option to ext3/4?

On Tue, Apr 10, 2007 at 02:08:26PM +0200, Jörn Engel wrote:
> On Tue, 10 April 2007 07:27:18 -0400, Theodore Tso wrote:
> > 
> > I suppose what you could do is to read in the journal, and use it to
> > create an remapping table so that when you want to read block #5126,
> > and block number 5126 is in the journal, to read the journal version
> > of the block instead of the one on disk.  That would allow for safe
> > access to a filesystem being mounted read-only without the journal
> > being present.
> 
> Another option would be to access the medium through a mapping inode,
> replay the journal into the mapping inode and _not_ flush the dirty
> pages.  But as long as a remapping table is sufficient for ext3 journal
> format, such a table should be simpler and faster.

Or you could make a snapshot with device-mapper and then mount it.
Requires some free disk space somewhere (or a hack with loop on
tmpfs), but should be doable today.

-- 
Mathematics is the supreme nostalgia of our time.
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