linux-ext4 - Re: [PATCH 2/2] jbd2: fix descriptor block size handling errors with journal

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Date:	Mon, 25 Aug 2014 22:44:24 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org, TR Reardon <thomas_reardon@...mail.com>
Subject: Re: [PATCH 2/2] jbd2: fix descriptor block size handling errors with
 journal_csum

On Fri, Aug 15, 2014 at 01:43:59PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@...cle.com>
> 
> It turns out that there are some serious problems with the on-disk
> format of journal checksum v2.  The foremost is that the function to
> calculate descriptor tag size returns sizes that are too big.  This
> causes alignment issues on some architectures and is compounded by the
> fact that some parts of jbd2 use the structure size (incorrectly) to
> determine the presence of a 64bit journal instead of checking the
> feature flags.
> 
> Therefore, introduce journal checksum v3, which enlarges the
> descriptor block tag format to allow for full 32-bit checksums of
> journal blocks, fix the journal tag function to return the correct
> sizes, and fix the jbd2 recovery code to use feature flags to
> determine 64bitness.
> 
> Add a few function helpers so we don't have to open-code quite so
> many pieces.
> 
> Switching to a 16-byte block size was found to increase journal size
> overhead by a maximum of 0.1%, to convert a 32-bit journal with no
> checksumming to a 32-bit journal with checksum v3 enabled.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> Reported-by: TR Reardon <thomas_reardon@...mail.com>

Thanks, applied.

					- Ted
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