Date: Mon, 25 Jan 2021 14:16:33 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: d@delphij.net Cc: freebsd-standards@freebsd.org, Jilles Tjoelker <jilles@freebsd.org>, Ed Maste <emaste@freebsd.org>, Xin Li <delphij@delphij.net>, Marshall Kirk McKusick <mckusick@freebsd.org> Subject: Re: _POSIX_C_SOURCE and S_IFMT macros Message-ID: <YA62oUzcLwL/bUNh@kib.kiev.ua> In-Reply-To: <69977864-0a68-909d-8ecb-1d72c0ec0ef9@delphij.net> References: <69977864-0a68-909d-8ecb-1d72c0ec0ef9@delphij.net>
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On Mon, Jan 25, 2021 at 01:04:25AM -0800, Xin Li via freebsd-standards wrote: > Hi, > > I recently discovered [1] a difference between FreeBSD's handling of > _POSIX_C_SOURCE and what I have observe on Linux and macOS systems, > basically, if a program defines _POSIX_C_SOURCE to 200809L, but did not > define _XOPEN_SOURCE, we will not define S_IFMT when sys/stat.h is included. > > It appears that the glibc version of sys/stat.h won't define it either, > but their fcntl.h would define it by having _POSIX_C_SOURCE >= 200809L > to define _USE_XOPEN2K8 and expose it. > > A quick glance on my Macbook suggests that they were defining the S_IFMT > macros unconditionally. > > Based on my research, hiding these macros started in revision 40491 of > CSRG repository ( > https://svnweb.freebsd.org/csrg?view=revision&revision=40491 ); NetBSD > chose to make the macro visible when _XOPEN_SOURCE in revision 1.34 and > expanded the visibility scope to also cover _NETBSD_SOURCE. > > Do we need to hide these with 200809L when _XOPEN_SOURCE is not defined? > If I'm reading the standards correctly, I think we are required to > define these in modern POSIX revisions? > > > > [1] When building pigz (https://github.com/madler/pigz), I got: > > cc -O3 -Wall -Wextra -Wno-unknown-pragmas -Wcast-qual -c pigz.c -o pigz.o > pigz.c:3817:47: error: use of undeclared identifier 'S_IFMT' > if (stat(from, &st) != 0 || (st.st_mode & S_IFMT) != S_IFREG) > ^ > [...] In my copy of IEEE Std 1003.1™-2017 S_IFMT and related S_IF<type> symbols are specified as provided by sys/stat.h. fcntl.h (not sys/fcntl.h, which is not specified by POSIX at all) does not require export of S_IF*. So I think S_IF symbols listed in POSIX standard should be provided by sys/stat.h under some value of POSIX_C_SOURCE, but I did not dig to see which should be the guard value. Most likely 200809 is fine.
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