linux-ext4 - Re: [Q] ext3 mkfs: zeroing journal blocks

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Message-ID: <20090511193514.GF21518@mit.edu>
Date:	Mon, 11 May 2009 15:35:14 -0400
From:	Theodore Tso <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Andreas Dilger <adilger@....com>,
	Alexander Shishkin <alexander.shishckin@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [Q] ext3 mkfs: zeroing journal blocks

On Mon, May 11, 2009 at 01:44:18PM -0500, Eric Sandeen wrote:
> Andreas Dilger wrote:
> 
> > The reason that the journal is zeroed is because there is some chance
> > that old (valid at the time) transaction headers and commit blocks might
> > be in the journal and could accidentally be "recovered" and cause bad
> > corruption of the filesystem.
> 
> But I guess the question is, why isn't a normal internal log zeroed?
> 
> If I'm reading it right only external logs get this treatment, and I
> think that's what generated the original question from Alexander.

Internal journals are indeed cleared.  Check out write_journal_inode()
in lib/ext2fs/mkjournal.c, which calls ext2fs_block_iterate() passing
in the callback function mkjournal_proc(), which calls
ext2fs_zero_blocks().

						- Ted
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