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Date: Thu, 29 Sep 2016 10:29:18 -0700
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 46/63] xfs: CoW shared EOF block when truncating file
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To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: david@fromorbit.com, linux-xfs@vger.kernel.org

On Tue, Sep 27, 2016 at 07:58:32PM -0700, Darrick J. Wong wrote:
> When shrinking a file, the VFS zeroes everything in the associated
> page between the new EOF and the previous EOF to avoid leaking data.
> If this block is shared we need to CoW it before the VFS does its
> zeroing to avoid corrupting the other files.

This shouldn't be needed. Zeroing the EOF block goes through the
iomap interface, which should handle the COW case properly.