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

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Message-ID: <4DA70BD3.1070409@draigBrady.com>
Date:	Thu, 14 Apr 2011 15:59:31 +0100
From:	Pádraig Brady <P@...igBrady.com>
To:	xfs-oss <xfs@....sgi.com>, linux-ext4@...r.kernel.org
CC:	Markus Trippelsdorf <markus@...ppelsdorf.de>, coreutils@....org
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

On 14/04/11 15:02, Markus Trippelsdorf wrote:
>>> Hi Pádraig,
>>>
>>> here you go:
>>> + filefrag -v unwritten.withdata                                                                                                                     
>>> Filesystem type is: ef53                                                                                                                             
>>> File size of unwritten.withdata is 5120 (2 blocks, blocksize 4096)                                                                                   
>>>  ext logical physical expected length flags                                                                                                          
>>>    0       0   274432            2560 unwritten,eof                                                                                                  
>>> unwritten.withdata: 1 extent found
>>>
>>> Please notice that this also happens with ext4 on the same kernel. 
>>> Btrfs is fine.
>>
> `filefrag -vs` fixes the issue on both xfs and ext4.

So in summary, currently on (2.6.39-rc3), the following
will (usually?) report a single unwritten extent,
on both ext4 and xfs

  fallocate -l 10MiB -n k
  dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k
  filefrag -v k # grep for an extent without unwritten || fail

This particular issue has been discussed so far at:
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8411
Note there it was stated there that ext4 had this
fixed as of 2.6.39-rc1, so maybe there is something lurking?

cheers,
Pádraig.
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