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

Eric Sandeen
2011-04-14T15:52:56Z

On 4/14/11 10:52 AM, Pádraig Brady wrote:
> On 14/04/11 16:50, Eric Sandeen wrote:
>> 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?
>
> Well that preallocate test is failing for him
> when the source file is either on ext4 or xfs.
> He noticed the issue initially on XFS when copying
> none preallocated files, so XFS probably just has
> the general issue of needing a sync before fiemap,
> where as EXT4 just has this preallocate one
> (though I've not seen it myself).
>
> cheers,
> Pádraig.
>

well, if I simply take the preallocation step out of the testcase, it works fine on xfs without a sync.

So I still don't know what Markus hit...

-Eric