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

To: Pádraig Brady <P@xxxxxxxxxxxxxx>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 14 Apr 2011 10:50:10 -0500
Cc: xfs-oss <xfs@xxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, coreutils@xxxxxxx, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
In-reply-to: <4DA70BD3.1070409@xxxxxxxxxxxxxx>
References: <20110414102608.GA1678@xxxxxxxxxxxxxx> <20110414120635.GB1678@xxxxxxxxxxxxxx> <20110414140222.GB1679@xxxxxxxxxxxxxx> <4DA70BD3.1070409@xxxxxxxxxxxxxx>
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On 4/14/11 9:59 AM, Pádraig Brady wrote:
> 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

right, that's what I see too in testing.

But would the coreutils install have done a preallocation of the destination 
file?

Otherwise this looks like a different bug...

> 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?

ext4 got a fix, but not xfs, I guess.  My poor brain can't remember, I think I 
started looking into it, but it's clearly still broken.

Still, I don't know for sure what happened to Markus - did something 
preallocate, in his case?

-Eric
 
> cheers,
> Pádraig.
> 
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