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

Eric Sandeen
2011-04-19T03:02:15Z

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.

-Eric