在 2011-4-18，下午6:03， Joerg Schilling 写道：
> "jeff.liu" <jeff....@oracle.com> wrote:
>
>> Hello List,
>>
>> I am trying to fetch the data/hole info of a sparse file through the
>> lseek(SEEK_HOLE/SEEK_DATA)
>> stuff, the result of fpathconf(..., _PC_MIN_HOLE_SIZE) is ok, so I think
>> this interface is supported
>> on my testing ZFS, but SEEK_HOLE always return the sparse file total size
>> instead of the desired
>> first hole start offset.
>
> Maybe you did not create the file correctly.
>
> If you like to create a file of a specific size that only contains one single
> hole, there is a way to do this using star:
>
> mkfile <size> some-file # create a file of the desired
> size
> star -c f=xx.tar -meta some-file # archive the meta data only
> rm some-file # remove original file
> star -x -xmeta -force-hole f=xx.tar # let star create an empty file of the
> # same size
>
> This will try to create a file that has one hole but no data in case the
> filesystem supports to do this.
>
> For UFS, such a file e.g. needs to be a multiple of 8k in size. This is
> because
> holes in UFS need to be aligned at 8k boundaries and need to be a multiple of
> 8k in size.
>
>
> A recent star can be found in the schily source consolidation:
>
> ftp://ftp.berlios.de/pub/schily/
>
>
> star is part of Schillix-ON (a free OpenSolaris fork).
Thanks for your info!
Actually, I'd like to create a sparse file with both data and holes to test a
patch I am working on, it was wrote for Coreutils to optimize sparse file
reading, especially for cp(1).
I had took a look at the source code of Star before, and I was wondering of
comments at start/hole.c: sparse_file(fp, info) at that time,
line: 1240 if (pos >= info->f_size) { /* Definitely not
sparse */
Now, I am still not sure why the returned 'pos' could larger than
'info->f_size' in some cases, I guess it should be equal to the f_size if the
target file is not sparse, Am I missing something here?
For the sparse file I created via python -c "f=open('sparse', 'w');
f.seek(40960); f.write('BYE'); f.close()", IMHO, it is a right way to create
a sparse file conventionally, but it is too small to spanning across
multiple blocks, so ZFS allocate it as an non-sparse single block file just as
Victor's response.
Regards,
-Jeff
>
> Jörg
>
> --
> EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
> j...@cs.tu-berlin.de (uni)
> joerg.schill...@fokus.fraunhofer.de (work) Blog:
> http://schily.blogspot.com/
> URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
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