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

[Eric Sandeen]

On 4/14/11 11:03 AM, Markus Trippelsdorf wrote:
> On 2011.04.14 at 10:56 -0500, Eric Sandeen wrote:

...

>> 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...
> 
> Maybe it's delalloc:
> 
> x4 /tmp # dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k       
>                                                                         
> 10+0 records in
> 10+0 records out
> 5120 bytes (5.1 kB) copied, 0.0021822 s, 2.3 MB/s
> x4 /tmp # filefrag -v k 
> Filesystem type is: 58465342
> File size of k is 5120 (2 blocks, blocksize 4096)
>  ext logical physical expected length flags
>    0       0        0              16 unknown,delalloc,eof
> k: 1 extent found
> x4 /tmp # sync
> x4 /tmp # filefrag -v k 
> Filesystem type is: 58465342
> File size of k is 5120 (2 blocks, blocksize 4096)
>  ext logical physical expected length flags
>    0       0 26960045              16 eof
> k: 1 extent found
> 

well filefrag still returns that it knows of a valid range from logical blocks 
0 to 16, so cp should have something to copy...

-Eric