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Re: 2 minor nits with mmap documentation page


From: Eric Gallager
Subject: Re: 2 minor nits with mmap documentation page
Date: Fri, 15 Jul 2022 21:02:28 -0400

On Thu, Jul 14, 2022 at 4:14 PM Bruno Haible <bruno@clisp.org> wrote:
>
> Hi,
>
> Eric Gallager wrote:
> > Hi, I was just writing because I noticed a few nits with gnulib's
> > documentation of mmap here:
> > https://www.gnu.org/software/gnulib/manual/html_node/mmap.html
> > 1. there's a missing close-parenthesis after "even without MAP_FIXED"
>
> Thanks; fixed:
> https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=5d2d12d7b5aeb023a2e45f5625a07777564caa27
>
> > 2. there's no discussion of how sometimes MAP_ANONYMOUS is written as
> > just MAP_ANON instead.
>
> This is an issue with the header file <sys/mman.h>, not with the function
> mmap(). Therefore it would have to be documented in
> https://www.gnu.org/software/gnulib/manual/html_node/sys_002fmman_002eh.html
>
> But in fact, POSIX does not require MAP_ANONYMOUS nor MAP_ANON, see
> https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/basedefs/sys_mman.h.html,
> and Gnulib does not correct it (one way or the other).
>
> > This GitHub issue for libressl-portable has a
> > (probably outdated) table covering which platforms support which
> > spelling: https://github.com/libressl-portable/portable/issues/24
>
> Gnulib also has this info, in m4/mmap-anon.m4 (dating from 2009):
>

OK, would it be worthwhile to at least add a cross-reference, then?

> # - On Linux, AIX, OSF/1, Solaris, Cygwin, Interix, Haiku, both MAP_ANONYMOUS
> #   and MAP_ANON exist and have the same value.
> # - On HP-UX, only MAP_ANONYMOUS exists.
> # - On Mac OS X, FreeBSD, NetBSD, OpenBSD, Minix, only MAP_ANON exists.
> # - On IRIX, neither exists, and a file descriptor opened to /dev/zero must be
> #   used.
>
> Meanwhile, Mac OS X and the BSDs also support both spellings:
> # - On Linux, Mac OS X, FreeBSD, NetBSD, OpenBSD, AIX, OSF/1, Solaris, Cygwin,
> #   Interix, Haiku, both MAP_ANONYMOUS and MAP_ANON exist and have the same 
> value.
> # - On HP-UX, only MAP_ANONYMOUS exists.
> # - On Minix, only MAP_ANON exists.
> # - On IRIX, neither exists, and a file descriptor opened to /dev/zero must be
> #   used.
>
> HP-UX, Minix, IRIX are no longer relevant for most programs. Therefore it's
> nowadays OK to use either MAP_ANONYMOUS or MAP_ANON, and both will work.
>
> Bruno
>
>
>



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