linux-ext4 - Re: [PATCH 1/5] ext4: Support for checksumming from journal triggers

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Date:   Thu, 22 Jul 2021 10:52:23 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/5] ext4: Support for checksumming from journal triggers

On Mon, Jul 12, 2021 at 05:40:05PM +0200, Jan Kara wrote:
> JBD2 layer support triggers which are called when journaling layer moves
> buffer to a certain state. We can use the frozen trigger, which gets
> called when buffer data is frozen and about to be written out to the
> journal, to compute block checksums for some buffer types (similarly as
> does ocfs2). This avoids unnecessary repeated recomputation of the
> checksum (at the cost of larger window where memory corruption won't be
> caught by checksumming) and is even necessary when there are
> unsynchronized updaters of the checksummed data.
> 
> So add argument to ext4_journal_get_write_access() and
> ext4_journal_get_create_access() which describes buffer type so that
> triggers can be set accordingly. This patch is mostly only a change of
> prototype of the above mentioned functions and a few small helpers. Real
> checksumming will come later.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

Looks good.  I would have preferred mention of the change to
ext4_walk_page_buffers in the commit description, but I guess this was
considered one of the "few small helpers".  :-)

The WARN_ON_ONCE change in jbd2_journal_set_triggers is a somewhat
tangentially-related unrelated change, but I think I understand why it
was made.

Reviewed-by: Theodore Ts'o <tytso@....edu>

						- Ted