linux-kernel - Re: [PATCH 04/12] xfs: initialize ioma->flags in xfs_bmbt_to

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Message-ID: <20190625152120.GA8153@lst.de>
Date:   Tue, 25 Jun 2019 17:21:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/12] xfs: initialize ioma->flags in xfs_bmbt_to_iomap

On Tue, Jun 25, 2019 at 08:13:57AM -0700, Darrick J. Wong wrote:
> > This doesn't affect any existing user as they all get a zeroed iomap
> > passed from the caller in iomap.c.  It affects the writeback code
> > once it uses struct iomap as it overwrites a previously used iomap.
> 
> Then shouldn't this new writeback code zero the iomap before calling
> back into the filesystem, just to maintain consistent behavior?

The core code doesn't decide when to overwrite it, that ->map_blocks
method does that based on a few factors (including the data_seq/cow_seq
counters that are entirely inside xfs).