From 893100aa1069cfe6adb4d0da5ef456c6932183e9 Mon Sep 17 00:00:00 2001
From: kib <kib@FreeBSD.org>
Date: Thu, 19 Jun 2014 05:00:39 +0000
Subject: Add MAP_EXCL flag for mmap(2).  It should be combined with MAP_FIXED,
 and prevents the request from deleting existing mappings in the region,
 failing instead.

Reviewed by:	alc
Discussed with:	jhb
Tested by:	markj, pho (previous version, as part of the bigger patch)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
---
 lib/libc/sys/mmap.2 | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

(limited to 'lib/libc')

diff --git a/lib/libc/sys/mmap.2 b/lib/libc/sys/mmap.2
index 01cde0e..3dd8303 100644
--- a/lib/libc/sys/mmap.2
+++ b/lib/libc/sys/mmap.2
@@ -28,7 +28,7 @@
 .\"	@(#)mmap.2	8.4 (Berkeley) 5/11/95
 .\" $FreeBSD$
 .\"
-.Dd September 9, 2013
+.Dd June 19, 2014
 .Dt MMAP 2
 .Os
 .Sh NAME
@@ -141,6 +141,12 @@ argument must be 0.
 This flag is identical to
 .Dv MAP_ANON
 and is provided for compatibility.
+.It Dv MAP_EXCL
+This flag can only be used in combination with
+.Dv MAP_FIXED .
+Please see the definition of
+.Dv MAP_FIXED
+for the description of its effect.
 .It Dv MAP_FIXED
 Do not permit the system to select a different address than the one
 specified.
@@ -152,17 +158,21 @@ If
 is specified,
 .Fa addr
 must be a multiple of the pagesize.
-If a
+If
+.Dv MAP_EXCL
+is not specified, a successfull
 .Dv MAP_FIXED
-request is successful, the mapping established by
-.Fn mmap
-replaces any previous mappings for the process' pages in the range from
+request replaces any previous mappings for the process'
+pages in the range from
 .Fa addr
 to
 .Fa addr
 +
 .Fa len .
-Use of this option is discouraged.
+In contrast, if
+.Dv MAP_EXCL
+is specified, the request will fail if a mapping
+already exists within the range.
 .It Dv MAP_HASSEMAPHORE
 Notify the kernel that the region may contain semaphores and that special
 handling may be necessary.
@@ -393,6 +403,17 @@ argument was not -1.
 was specified and the
 .Fa offset
 argument was not 0.
+.It Bq Er EINVAL
+Both
+.Dv MAP_FIXED
+and
+.Dv MAP_EXCL
+were specified, but the requested region is already used by a mapping.
+.It Bq Er EINVAL
+.Dv MAP_EXCL
+was specified, but
+.Dv MAP_FIXED
+was not.
 .It Bq Er ENODEV
 .Dv MAP_ANON
 has not been specified and
-- 
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