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From: Michal Hocko <mhocko@kernel.org>
To: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: linux-api@vger.kernel.org, Khalid Aziz <khalid.aziz@oracle.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org, Florian Weimer <fweimer@redhat.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag
Date: Wed, 29 Nov 2017 15:45:24 +0100
Message-ID: <20171129144524.23518-1-mhocko@kernel.org> (raw)
In-Reply-To: <20171129144219.22867-1-mhocko@kernel.org>

From: Michal Hocko <mhocko@suse.com>

4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows to atomicaly
probe for a given address range.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 man2/mmap.2 | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/man2/mmap.2 b/man2/mmap.2
index 385f3bfd5393..622a7000de83 100644
--- a/man2/mmap.2
+++ b/man2/mmap.2
@@ -225,6 +225,18 @@ will fail.
 Because requiring a fixed address for a mapping is less portable,
 the use of this option is discouraged.
 .TP
+.B MAP_FIXED_SAFE (since 4.16)
+Similar to MAP_FIXED wrt. to the
+.I
+addr
+enforcement except it never clobbers a colliding mapped range and rather fail with
+.B EEXIST
+in such a case. This flag can therefore be used as a safe and atomic probe for the
+the specific address range. Please note that older kernels which do not recognize
+this flag can fallback to the hint based implementation and map to a different
+location. Any backward compatible software should therefore check the returning
+address with the given one.
+.TP
 .B MAP_GROWSDOWN
 This flag is used for stacks.
 It indicates to the kernel virtual memory system that the mapping
@@ -449,6 +461,12 @@ is not a valid file descriptor (and
 .B MAP_ANONYMOUS
 was not set).
 .TP
+.B EEXIST
+range covered by
+.IR addr , 
+.IR length
+is clashing with an existing mapping.
+.TP
 .B EINVAL
 We don't like
 .IR addr ,
-- 
2.15.0

  parent reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-29 14:42 [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Michal Hocko
2017-11-29 14:42 ` [PATCH 1/2] " Michal Hocko
2017-12-06  5:15   ` Michael Ellerman
2017-12-06  9:27     ` Michal Hocko
2017-12-06 10:02       ` Michal Hocko
2017-12-07 12:07   ` Pavel Machek
2017-11-29 14:42 ` [PATCH 2/2] fs, elf: drop MAP_FIXED usage from elf_map Michal Hocko
2017-11-29 17:45   ` Khalid Aziz
2017-11-29 14:45 ` Michal Hocko [this message]
2017-11-30  3:16   ` [PATCH] mmap.2: document new MAP_FIXED_SAFE flag John Hubbard
2017-11-30  8:23     ` Michal Hocko
2017-11-30  8:24   ` [PATCH v2] " Michal Hocko
2017-11-30 18:31     ` John Hubbard
2017-11-30 18:39       ` Michal Hocko
2017-11-29 15:13 ` [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Rasmus Villemoes
     [not found]   ` <b154b794-7a8b-995e-0954-9234b9446b31-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
2017-11-29 15:50     ` Michal Hocko
2017-11-29 22:15   ` Kees Cook
2017-11-29 22:12 ` Kees Cook
2017-11-29 22:25 ` Kees Cook
     [not found]   ` <CAGXu5jLa=b2HhjWXXTQunaZuz11qUhm5aNXHpS26jVqb=G-gfw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-11-30  6:58     ` Michal Hocko
2017-12-01 15:26       ` Cyril Hrubis
2017-12-06  4:51         ` Michael Ellerman
2017-12-06  4:54           ` Matthew Wilcox
2017-12-06  7:03             ` Matthew Wilcox
2017-12-06  7:33               ` John Hubbard
     [not found]                 ` <5f4fc834-274a-b8f1-bda0-5bcddc5902ed-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06  7:35                   ` Florian Weimer
2017-12-06  8:06                     ` John Hubbard
     [not found]                       ` <27ee1755-76d8-f086-5760-9c973b31108a-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06  8:54                         ` Florian Weimer
     [not found]               ` <20171206070355.GA32044-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2017-12-07  5:46                 ` Michael Ellerman
2017-12-07 19:14                   ` Kees Cook
     [not found]                     ` <CAGXu5jLWRQn6EaXEEvdvXr+4gbiJawwp1EaLMfYisHVfMiqgSA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-07 19:57                       ` Matthew Wilcox
2017-12-08  8:33                         ` Michal Hocko
     [not found]                           ` <20171208083315.GR20234-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-12-08 20:13                             ` Kees Cook
     [not found]                               ` <CAGXu5j+VupGmKEEHx-uNXw27Xvndu=0ObsBqMwQiaYPyMGD+vw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-08 20:57                                 ` Matthew Wilcox
2017-12-08 11:08                         ` Michael Ellerman
2017-12-08 14:27                           ` Pavel Machek
2017-12-08 20:31                             ` Cyril Hrubis
2017-12-08 20:47                             ` Florian Weimer
2017-12-08 14:33                           ` David Laight
2017-12-06  4:50       ` Michael Ellerman
     [not found]         ` <87zi6we9z2.fsf-W0DJWXSxmBNbyGPkN3NxC2scP1bn1w/D@public.gmane.org>
2017-12-06  7:33           ` Rasmus Villemoes
     [not found]             ` <a3b3129a-2626-a65e-59b0-68aada523723-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
2017-12-06  9:08               ` Michal Hocko
2017-12-07  0:19                 ` Kees Cook
2017-12-07  1:08                   ` John Hubbard

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