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

[Sunil Mushran]

On 08/20/2011 03:03 AM, Marco Stornelli wrote:
> 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.

Yes, the offset is from the start of the file.

And yes, same offset is ok. I think the word next should be
dropped from the definition. It is misleading.
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