From: john.hubbard@gmail.com
To: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: linux-man <linux-man@vger.kernel.org>,
linux-api@vger.kernel.org, Michael Ellerman <mpe@ellerman.id.au>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH] mmap.2: MAP_FIXED is no longer discouraged
Date: Fri, 1 Dec 2017 18:16:26 -0800 [thread overview]
Message-ID: <20171202021626.26478-1-jhubbard@nvidia.com> (raw)
From: John Hubbard <jhubbard@nvidia.com>
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 <jhubbard@nvidia.com>
---
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
next reply other threads:[~2017-12-02 2:16 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-02 2:16 john.hubbard [this message]
2017-12-02 15:05 ` [PATCH] mmap.2: MAP_FIXED is no longer discouraged Matthew Wilcox
2017-12-02 18:49 ` Jann Horn
2017-12-02 22:19 ` Matthew Wilcox
2017-12-03 0:22 ` John Hubbard
2017-12-03 4:06 ` John Hubbard
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171202021626.26478-1-jhubbard@nvidia.com \
--to=john.hubbard@gmail.com \
--cc=jhubbard@nvidia.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-man@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=mpe@ellerman.id.au \
--cc=mtk.manpages@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).