From mboxrd@z Thu Jan 1 00:00:00 1970 From: john.hubbard-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org Subject: [PATCH] mmap.2: MAP_FIXED is no longer discouraged Date: Fri, 1 Dec 2017 18:16:26 -0800 Message-ID: <20171202021626.26478-1-jhubbard@nvidia.com> Return-path: Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michael Kerrisk Cc: linux-man , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michael Ellerman , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, LKML , linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michal Hocko , John Hubbard List-Id: linux-api@vger.kernel.org From: John Hubbard MAP_FIXED has been widely used for a very long time, yet the man page still claims that "the use of this option is discouraged". The documentation assumes that "less portable" == "must be discouraged". Instead of discouraging something that is so useful and widely used, change the documentation to explain its limitations better. Signed-off-by: John Hubbard --- While reviewing Michal Hocko's man page update for MAP_FIXED_SAFE, I noticed that MAP_FIXED was no longer reflecting the current situation, so here is a patch to bring it into the year 2017. man2/mmap.2 | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/man2/mmap.2 b/man2/mmap.2 index 385f3bfd5..a5a8eb47a 100644 --- a/man2/mmap.2 +++ b/man2/mmap.2 @@ -222,8 +222,10 @@ part of the existing mapping(s) will be discarded. If the specified address cannot be used, .BR mmap () will fail. -Because requiring a fixed address for a mapping is less portable, -the use of this option is discouraged. +Software that aspires to be portable should use this option with care, keeping +in mind that the exact layout of a process' memory map is allowed to change +significantly between kernel versions, C library versions, and operating system +releases. .TP .B MAP_GROWSDOWN This flag is used for stacks. -- 2.15.1 -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html