On Wed Feb 23 11, Garrett Cooper wrote:
> On Wed, Feb 23, 2011 at 3:36 PM, Alexander Best <[email protected]> wrote:
> > On Wed Feb 23 11, Garrett Cooper wrote:
> >> On Feb 22, 2011, at 9:51 AM, John Baldwin wrote:
> >>
> >> > On Tuesday, February 22, 2011 11:46:05 am Garrett Cooper wrote:
> >> >> (Please bottom post)
> >> >>
> >> >> On Tue, Feb 22, 2011 at 8:31 AM, Andrew Duane <[email protected]>
> >> >> wrote:
> >> >>> I thought seeking past EOF was valid; writing something creates a file
> >> > with a hole in it. I always assumed that was standard semantics.
> >> >>
> >> >> That's with SET_HOLE/SET_DATA though, correct? If so, outside of
> >> >> that functionality I would assume relatively standard POSIX semantics.
> >> >
> >> > Err, no, you can always seek past EOF and then call write(2) to extend a
> >> > file
> >> > (it does an implicit ftruncate(2)). SEEK_HOLE and SEEK_DATA are
> >> > different,
> >> > they are just used to discover sparse regions within a file.
> >> >
> >> > From the manpage:
> >> >
> >> > The lseek() system call allows the file offset to be set beyond the
> >> > end
> >> > of the existing end-of-file of the file. If data is later written at
> >> > this point, subsequent reads of the data in the gap return bytes of
> >> > zeros
> >> > (until data is actually written into the gap).
> >>
> >> You're correct. Linux (Fedora 13) isn't POSIX compliant (this is
> >> from the official POSIX text):
> >>
> >> The lseek ( ) function shall allow the file offset to be set beyond the
> >> end of the existing data in the file. If data is later written at this
> >> point, subsequent reads of data in the gap shall return bytes with the
> >> value 0 until data is actually written into the gap.
> >
> > so except for reading from /dev/zero freebsd also isn't posix compliant,
> > right?
>
> Huh...? Please better explain what you mean here.
if i got this right when reading from /dev/{zero,null} and writing to
/dev/{zero,null} seeking past EOF should take place.
right now only reading from /dev/zero seeks correctly. writing to /dev/zero
and reading/writing to/from /dev/null will not seek, but remain at offset 0.
cheers.
alex
> Thanks,
> -Garrett
--
a13x
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