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Subject: Re: [PATCH, RFC] xfs: re-enable FIBMAP on reflink; disable for swap
References: <2eb759e5-2faa-67fd-5c16-c1d8edc42d02@redhat.com>
 <20180830162545.GA26816@lst.de>
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From: Eric Sandeen <sandeen@sandeen.net>
Message-ID: <65e818f2-885d-50a4-0d4a-7700c703c2af@sandeen.net>
Date: Thu, 30 Aug 2018 11:35:46 -0500
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To: Christoph Hellwig <hch@lst.de>, Eric Sandeen <sandeen@redhat.com>
Cc: linux-xfs <linux-xfs@vger.kernel.org>

On 8/30/18 11:36 AM, Christoph Hellwig wrote:
> On Thu, Aug 30, 2018 at 11:31:40AM -0500, Eric Sandeen wrote:
>> That's no reason to uniquely disallow it for reflinked files, though;
>> the problem is universal.  It's true for fiemap as well.  So I'm not sure
>> that's an argument against the patch?
> 
> fiemap at least tells you an extent is shared, bmap does not.

yes, so bmap is clearly the wrong interface to use if you want to
write directly to a file's blocks.  But if you know enough to check
the fiemap shared flag, you know enough to not use fibmap for that purpose...

-Eric