Re: [PATCH 1/4] fs: add SEEK_HOLE and SEEK_DATA flags

Marco Stornelli
2011-08-20T10:09:15Z

Il 20/08/2011 11:41, Marco Stornelli ha scritto:
> Hi,
>
> Il 28/06/2011 17:33, Josef Bacik ha scritto:
>> This just gets us ready to support the SEEK_HOLE and SEEK_DATA flags.
>> Turns out
>> using fiemap in things like cp cause more problems than it solves, so
>> lets try
>> and give userspace an interface that doesn't suck. We need to match
>> solaris
>> here, and the definitions are
>>
>> *o* If /whence/ is SEEK_HOLE, the offset of the start of the
>> next hole greater than or equal to the supplied offset
>> is returned. The definition of a hole is provided near
>> the end of the DESCRIPTION.
>>
>> *o* If /whence/ is SEEK_DATA, the file pointer is set to the
>> start of the next non-hole file region greater than or
>> equal to the supplied offset.
>>
>
> I'm implementing the SEEK_DATA/SEEK_HOLE management for pramfs and I've
> got some doubts about the right behavior:
>
> 1) when we use SEEK_DATA/SEEK_HOLE, the offset used in lseek means
> always the offset from the start of the file, right?
>
> 2) in case of a file with hole at the beginning and data at the end, if
> I do lseek(fd, 0, SEEK_HOLE) I should receive the end of the file
> because the idea is to search the *next* hole and we have always a
> virtual hole at the end of the file, right?

Just to be precise about this question: the alternative here, it's to
return the same position because we are already in a hole.

Marco