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

[Marco Stornelli]

Il 22/08/2011 17:57, Sunil Mushran ha scritto:
> > > Any proposal that differentiates between holes is wrong. It should not
> > > matter where the hole is.
> > >
> > > Think of it from the usage-pov.
> > >
> > > doff = 0;
> > > while ((doff = lseek(SEEK_DATA, doff)) != -ENXIO) {
> > > hoff = lseek(SEEK_HOLE, doff);
> > > read_offset = doff;
> > > read_len = hoff -doff;
> > > process();
> > > doff = hoff;
> > > }
> > >
> > > The goal is to make this as efficient as follows. Treating the last
> > > hole differently adds more code for no benefit.
> > Mmmm.....It seems that Josef has to be clear in this point. However I
> > looked for the seek hole test in xfs test suite, but I didn't find
> > anything. Btrfs guys, how have you got tested the implementation? What
> > do you think about this corner case? Al, what do you think about it?
>
>
> The following test was used to test the early implementations.
> http://oss.oracle.com/~smushran/seek_data/

Thank you very much!! I found another point. Your test fails with my 
implementation because here 
(http://www.austingroupbugs.net/view.php?id=415) says: "If whence is 
SEEK_DATA, the file offset shall be set to the smallest location of a 
byte not within a hole and not less than offset. It shall be an error if 
no such byte exists." So in this case I return ENXIO but the test 
expects another value. I have to say that there is a bit of confusion 
about the real behavior of this new feature :)

Marco
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