There may still be problems with this patch. After applying to 3.16.1, I am now getting "can't enable checksumming v2 and v3 at the same time" errors on mount. Initial mount/dismount work fine, but once fs is touched--forcing superblock update--it cannot be mounted anew.
Note results from dumpe2fs (without recent patches)
Journal backup: inode blocks
Checksum type: crc32c
Checksum: 0x39141b69
Journal features: journal_incompat_revoke journal_64bit journal_async_commit journal_checksum_v2 FEATURE_I4
Journal size: 128M
Journal length: 32768
Journal sequence: 0x00012aa4
Journal start: 0
Journal checksum type: crc32c
Journal checksum: 0x3952b695
Seems that the old v2 flag is not cleared on dismount?
--- Original Message ---
From: "Theodore Ts'o" <tytso@xxxxxxx>
Sent: August 25, 2014 10:44 PM
To: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Cc: linux-ext4@xxxxxxxxxxxxxxx, "TR Reardon" <thomas_reardon@xxxxxxxxxxx>
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@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Reported-by: TR Reardon <thomas_reardon@xxxxxxxxxxx>
Thanks, applied.
- Ted
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