[src/trunk]: src/lib/libc/sys Document the new MAP_ALIGNED() flag/macro, be m...

[atatat <atatat%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/713867575e90
branches:  trunk
changeset: 545541:713867575e90
user:      atatat <atatat%NetBSD.org@localhost>
date:      Thu Apr 10 18:22:47 2003 +0000

description:
Document the new MAP_ALIGNED() flag/macro, be more specific about what
values for fd are acceptable when using MAP_ANON, and add a short
paragraph describing (in short) the relationship between mmap()
allocations and the break.

Addresses PR kern/7935 and PR lib/20803.

diffstat:

 lib/libc/sys/mmap.2 |  31 ++++++++++++++++++++++++-------
 1 files changed, 24 insertions(+), 7 deletions(-)

diffs (69 lines):

diff -r 3276e89012be -r 713867575e90 lib/libc/sys/mmap.2
--- a/lib/libc/sys/mmap.2       Thu Apr 10 18:04:20 2003 +0000
+++ b/lib/libc/sys/mmap.2       Thu Apr 10 18:22:47 2003 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: mmap.2,v 1.28 2003/03/31 03:02:59 perry Exp $
+.\"    $NetBSD: mmap.2,v 1.29 2003/04/10 18:22:47 atatat Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"    The Regents of the University of California.  All rights reserved.
@@ -33,7 +33,7 @@
 .\"
 .\"    @(#)mmap.2      8.4 (Berkeley) 5/11/95
 .\"
-.Dd May 11, 1995
+.Dd April 10, 2003
 .Dt MMAP 2
 .Os
 .Sh NAME
@@ -123,13 +123,23 @@
 the following values:
 .Pp
 .Bl -tag -width MAP_FIXEDX
+.It Dv MAP_ALIGNED(n)
+Request that the allocation be aligned to the given boundary.
+The parameter
+.Ar n
+should be the base 2 logarithm of the desired alignment (e.g. to
+request alignment to 16K, use 14 as the value for n).
+The alignment must be equal to or greater than the platform's page
+size as returned by
+.Xr sysconf 3
+with the
+.Dv _SC_PAGESIZE
+request.
 .It Dv MAP_ANON
 Map anonymous memory not associated with any specific file.
-The file descriptor used for creating
+The file descriptor is not used for creating
 .Dv MAP_ANON
-regions is used only for
-naming, and may be specified as \-1 if no name is associated with the
-region.
+regions, and must be specified as \-1.
 .It Dv MAP_FILE
 Mapped from a regular file or character-special device memory.
 .It Dv MAP_FIXED
@@ -173,6 +183,12 @@
 in which
 the file descriptor argument specifies a file or device to which swapping
 should be done.
+.Pp
+If
+.Dv MAP_FIXED
+is not specified, the system will attempt to place the mapping in an
+unused portion of the address space chosen to minimize possible
+collision between mapped regions and the heap.
 .Sh RETURN VALUES
 Upon successful completion,
 .Nm mmap
@@ -259,7 +275,8 @@
 .Xr mprotect 2 ,
 .Xr msync 2 ,
 .Xr munmap 2 ,
-.Xr getpagesize 3
+.Xr getpagesize 3 ,
+.Xr sysconf 3
 .Sh BUGS
 The
 .Dv MAP_COPY