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

[Jim Meyering]

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