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

Eric Sandeen
2011-04-14T15:46:51Z

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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