linux-ext4 - Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

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Message-ID: <87fwpbqs8d.fsf@rho.meyering.net>
Date:	Thu, 21 Apr 2011 22:12:02 +0200
From:	Jim Meyering <jim@...ering.net>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	Ted Ts'o <tytso@....edu>, Andreas Dilger <adilger@...ger.ca>,
	Dave Chinner <david@...morbit.com>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	xfs-oss <xfs@....sgi.com>,
	"coreutils\@gnu.org" <coreutils@....org>,
	"linux-ext4\@vger.kernel.org" <linux-ext4@...r.kernel.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

Eric Sandeen wrote:
> On 4/18/11 9:59 PM, Ted Ts'o wrote:
> ...
>> Maybe coreutils will need to use FIEMAP_FLAG_SYNC initially, since
>> it's the only way to guarantee correct behaviour for XFS.  But I would
>> really rather that be the long-term way we leave things!
>
> XFS ... or ext4:
>
> # xfs_io -Ff -c "falloc 0 1m" -c "pwrite 0 512k" testfile;
> /root/fiemap-test testfile
> wrote 524288/524288 bytes at offset 0
> 512 KiB, 128 ops; 0.0000 sec (161.342 MiB/sec and 41303.6463 ops/sec)
> start 0 length -1 flags 0x0 count 32
> ext: 0 logical: [ 0..  255] phys: 34048..  34303 flags: 0x801 tot: 256
>
> # uname -r
> 2.6.39-0.rc3.git2.0.fc16.x86_64
>
> Above is on ext4.  It behaves exactly like XFS in my testing; data in
> the page cache does not cause fiemap to return anything other than
> "unwritten" for preallocated extents.

Thanks for the feedback.
In case anyone wants to test or review,
I've just made a coreutils snapshot:

  http://thread.gmane.org/gmane.comp.gnu.coreutils.general/1108
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