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Date: Tue, 15 Nov 2016 00:55:26 -0800
From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Qu Wenruo <quwenruo@cn.fujitsu.com>, linux-xfs@vger.kernel.org,
        fstests@vger.kernel.org, btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: About difference in extent sharing in btrfs and xfs
Message-ID: <20161115085526.GA18347@infradead.org>
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 <20161115074715.GA23680@birch.djwong.org>
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On Mon, Nov 14, 2016 at 11:47:15PM -0800, Darrick J. Wong wrote:
> XFS doesn't split the extent either, internally.  The FIEMAP
> implementation cross-references extent data with the refcount records,
> using extra struct fiemap_extent to report precisely which blocks are
> shared and which aren't.  ocfs2 exhibits the same behavior.

And I think exact reporting of already shared extents in FIEMAP is
extremely important - independent of the internal implementation btrfs
should report the extents correctly.