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

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Date:	Tue, 2 Sep 2014 15:28:33 -0400
From:	TR Reardon <thomas_reardon@...mail.com>
To:	Theodore Ts'o <tytso@....edu>,
	"Darrick J. Wong" <darrick.wong@...cle.com>
CC:	<linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] jbd2: fix descriptor block size handling errors
 with journal_csum

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@....edu>
Sent: August 25, 2014 10:44 PM
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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