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Cc: Alexander Best <arundel@freebsd.org>, Garrett Cooper <gcooper@freebsd.org>
Subject: Re: seeking into /dev/{null,zero}
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On Tuesday, February 22, 2011 11:46:05 am Garrett Cooper wrote:
> (Please bottom post)
>=20
> On Tue, Feb 22, 2011 at 8:31 AM, Andrew Duane <aduane@juniper.net> wrote:
> > I thought seeking past EOF was valid; writing something creates a file=
=20
with a hole in it. I always assumed that was standard semantics.
>=20
>     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 fi=
le=20
(it does an implicit ftruncate(2)).  SEEK_HOLE and SEEK_DATA are different,=
=20
they are just used to discover sparse regions within a file.

=46rom 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 ze=
ros
     (until data is actually written into the gap).

=2D-=20
John Baldwin