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Date: Thu, 24 Feb 2011 20:26:25 +1100
From: Dave Chinner <david@fromorbit.com>
Subject: Re: write 'O_DIRECT' file w/odd amount of data: desirable result?
Message-ID: <20110224092625.GA3087@dastard>
References: <4D648D7D.7040500@tlinx.org> <4D64E2BB.7010000@draigBrady.com>
	<4D654C2E.2000703@tlinx.org>
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To: "Linda A. Walsh" <lkml@tlinx.org>
Cc: PXXdraig Brady <P@draigBrady.com>, LKML <linux-kernel@vger.kernel.org>, xfs-oss <xfs@oss.sgi.com>

On Wed, Feb 23, 2011 at 10:04:30AM -0800, Linda A. Walsh wrote:
> 
> 
> FWIW -- xfs-oss, included as 'last line' was of minor interest; known bug on
> this kernel?:
> Linux Ishtar 2.6.35.7-T610-Vanilla-1 #2 SMP PREEMPT Mon Oct 11
> 17:19:41 PDT 2010 x86_64 x86_64 x86_64 GNU/Linux
....
> Of *SIGNIFICANT* note.  In trying to create an empty file of the size
> used, from scratch, using 'xfs_mkfile', I got an error:
> 
> > xfs_mkfile 5776419696 testfile
> pwrite64: Invalid argument

xfs_mkfile does not create an "empty" file. It creates a file that
is full of zeros.

iAnd you're getting that erro because:

5776419696 / 512 = 11,282,069.7188

the last write is not a multiple of the sector size and xfs_mkfile
uses direct IO. It has always failed when you try to do this. If you
want to create allocated, zeroed files of abitrary size, then use:

xfs_io -f -c "truncate $size" -c "resvsp 0 $size" $filename

to preallocate it. it'll be much, much faster than xfs_mkfile.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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