From: Paul Eggert <eggert@CS.UCLA.EDU>
Subject: Re: bug#6131: [PATCH]: fiemap support for efficient sparse file copy
Date: Tue, 15 Jun 2010 14:11:01 -0700
Message-ID: <4C17EC65.6040406@cs.ucla.edu>
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Cc: "jeff.liu" <jeff.liu@oracle.com>, Jim Meyering <jim@meyering.net>,
	Tao Ma <tao.ma@oracle.com>, bug-coreutils@gnu.org,
	Joel Becker <Joel.Becker@oracle.com>,
	Chris Mason <chris.mason@oracle.com>,
	"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>
To: Sunil Mushran <sunil.mushran@oracle.com>
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Sunil Mushran wrote:

> SEEK_HOLE/DATA also have the same problem with active files.

Yes, that's true if 'cp' is copying a file while someone else is writing to it.
But the case we're worried about is when 'cp' starts copying a file immediately
after someone else has finished writing to it but data has not been sent to
disk; in that case SEEK_HOLE/DATA should work just as well as the fiemap ioctl.