From: Christoph Hellwig <hch@infradead.org>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
Date: Fri, 15 Apr 2011 13:16:29 -0400
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Cc: Dave Chinner <david@fromorbit.com>,
	P?draig Brady <P@draigBrady.com>, linux-ext4@vger.kernel.org,
	Eric Sandeen <sandeen@sandeen.net>, coreutils@gnu.org,
	Markus Trippelsdorf <markus@trippelsdorf.de>,
	xfs-oss <xfs@oss.sgi.com>
To: Jim Meyering <jim@meyering.net>
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On Fri, Apr 15, 2011 at 10:53:48AM +0200, Jim Meyering wrote:
> Can you or anyone else point to authoritative documentation
> (or even a summary of those "discussions") of FIEMAP semantics?

A large part of the problem is that there's none and the semantics
is a hode-podge of random flags that mostly make little sense
outside of fs developers debugging the layout that we created.  The
closest to a description is Documentation/filesystems/fiemap.txt
in the kernel tree, but that doesn't document most of the delicate
points.