[apple/xnu.git] / bsd / man / man2 / mmap.2

.\"	$NetBSD: mmap.2,v 1.5 1995/06/24 10:48:59 cgd Exp $
.\"
.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)mmap.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt MMAP 2
.Os BSD 4
.Sh NAME
.Nm mmap
.Nd map files or devices into memory
.Sh SYNOPSIS
.Fd #include <sys/mman.h>
.Ft void *
.Fo mmap
.Fa "void *addr"
.Fa "size_t len"
.Fa "int prot"
.Fa "int flags"
.Fa "int fildes"
.Fa "off_t offset"
.Fc
.Sh DESCRIPTION
The
.Nm mmap
function causes the pages starting at
.Fa addr
and continuing for at most
.Fa len
bytes to be mapped from the object described by
.Fa fildes ,
starting at byte offset
.Fa offset .
If
.Fa offset
or
.Fa len
is not a multiple of the pagesize, the mapped region may extend past the
specified range.
.Pp
If
.Fa addr
is non-zero, it is used as a hint to the system.
(As a convenience to the system, the actual address of the region may differ
from the address supplied.)
If
.Fa addr
is zero, an address will be selected by the system.
The actual starting address of the region is returned.
A successful
.Fa mmap
deletes any previous mapping in the allocated address range.
.Pp
The protections (region accessibility) are specified in the
.Fa prot
argument by
.Em or Ns 'ing
the following values:
.Pp
.Bl -tag -width MAP_FIXEDX
.It Dv PROT_EXEC
Pages may be executed.
.It Dv PROT_READ
Pages may be read.
.It Dv PROT_WRITE
Pages may be written.
.El
.Pp
The
.Fa flags
parameter specifies the type of the mapped object, mapping options,
and whether modifications made to the mapped copy of the page
are private to the process (copy-on-write)
or are to be shared with other references.
Sharing, mapping type, and options are specified in the
.Fa flags
argument by
.Em or Ns 'ing
the following values:
.Pp
.Bl -tag -width MAP_HASSEMAPHOREX
.It Dv MAP_ANON
Map anonymous memory not associated with any specific file.
Mac OS X specific: the file descriptor used for creating
.Dv MAP_ANON
regions can be used to pass some Mach VM flags, and can 
be specified as \-1 if no such flags are associated with 
the region.  Mach VM flags are defined in 
<mach/vm_statistics.h> and the ones that currently apply 
to 
.Nm mmap
are:
.Pp
VM_FLAGS_PURGABLE	to create Mach purgable (i.e. volatile) memory
VM_MAKE_TAG(tag)	to associate an 8-bit tag with the region
.Pp
<mach/vm_statistics.h> defines some preset tags (with a VM_MEMORY_ prefix).
Users are encouraged to use tags between 240 and 255.
Tags are used by tools such as vmmap(1) to help identify specific memory regions.
.It Dv MAP_FILE
Mapped from a regular file or character-special device memory.  (This is
the default mapping type, and need not be specified.)
.It Dv MAP_FIXED
Do not permit the system to select a different address than the one
specified.
If the specified address cannot be used,
.Nm mmap
will fail.
If MAP_FIXED is specified,
.Fa addr
must be a multiple of the pagesize.
Use of this option is discouraged.
.It Dv MAP_HASSEMAPHORE
Notify the kernel that the region may contain semaphores and that special
handling may be necessary.
.It Dv MAP_PRIVATE
Modifications are private (copy-on-write).
.It Dv MAP_SHARED
Modifications are shared.
.It Dv MAP_NOCACHE
Pages in this mapping are not retained in the kernel's memory cache.
If the system runs low on memory, pages in MAP_NOCACHE mappings will be among
the first to be reclaimed.
This flag is intended for mappings that have little locality and 
provides a hint to the kernel that pages in this mapping are unlikely to be needed
again in the near future.
.El
.Pp
Conforming applications must specify either MAP_PRIVATE or MAP_SHARED.
.Pp
The 
.Xr close 2
function does not unmap pages, see
.Xr munmap 2
for further information.
.Pp
The current design does not allow a process to specify the location of
swap space.
In the future we may define an additional mapping type,
.Dv MAP_SWAP ,
in which
the file descriptor argument specifies a file or device to which swapping
should be done.
.Sh RETURN VALUES
Upon successful completion,
.Nm mmap
returns a pointer to the mapped region.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn Mmap
will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
.Fa Fildes
is not open for reading.
.\" ===========
.It Bq Er EACCES
The flags
.Dv PROT_WRITE
and
.Dv MAP_SHARED
are specified as part of the
.Fa flags
and
.Fa prot
parameters and
.Fa fildes
is not open for writing.
.\" ===========
.It Bq Er EBADF
.Fa fildes
is not a valid file descriptor for an open file.
.It Bq Er EINVAL
.Dv MAP_FIXED
is specified and the
.I addr
parameter is not page aligned.
.\" ===========
.It Bq Er EINVAL
.Fa fildes
does not reference a regular or character special file.
.\" ===========
.It Bq Er EINVAL
.Fa flags
does not include either MAP_PRIVATE or MAP_SHARED.
.\" ===========
.It Bq Er EINVAL
.Fa len
is not greater than zero.
.\" ===========
.It Bq Er EINVAL
.Fa offset
is not a multiple of the page size,
as returned by
.Xr sysconf 3 .
.\" ===========
.It Bq Er EMFILE
The limit on mapped regions (per process or system) is exceeded.
.\" ===========
.It Bq Er ENODEV
The file type for
.Fa fildes
is not supported for mapping.
.\" ===========
.It Bq Er ENOMEM
.Dv MAP_FIXED
is specified and the address range specified
exceeds the address space limit for the process.
.\" ===========
.It Bq Er ENOMEM
.Dv MAP_FIXED
is specified and the address specified by the
.Fa addr
parameter isn't available.
.\" ===========
.It Bq Er ENOMEM
.Dv MAP_ANON
is specified and insufficient memory is available.
.\" ===========
.It Bq Er ENXIO
Addresses in the specified range are invalid for fildes.
.\" ===========
.It Bq Er EOVERFLOW
Addresses in the specified range exceed the maximum offset
set for fildes.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/mman.h>
.Pp
The include file
.In sys/types.h
is necessary.
.Sh COMPATIBILITY
.Fn mmap
now returns with
.Va errno
set to EINVAL in places that historically succeeded.
The rules have changed as follows:
.Bl -bullet
.It
The
.Fa flags
parameter must specify either MAP_PRIVATE or MAP_SHARED.
.It
The
.Fa size
parameter must not be 0.
.It
The
.Fa off
parameter must be a multiple of pagesize,
as returned by
.Fn sysconf .
.El
.Sh "SEE ALSO"
.Xr getpagesize 2 ,
.Xr madvise 2 ,
.Xr mincore 2 ,
.Xr mlock 2 ,
.Xr mprotect 2 ,
.Xr msync 2 ,
.Xr munmap 2 ,
.Xr sysconf 3 ,
.Xr compat 5
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: mmap.2,v 1.5 1995/06/24 10:48:59 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)mmap.2 8.1 (Berkeley) 6/4/93
	35	.\"
	36	.Dd June 4, 1993
	37	.Dt MMAP 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm mmap
	41	.Nd map files or devices into memory
	42	.Sh SYNOPSIS
9bccf70c A	43	.Fd #include <sys/mman.h>
9bccf70c A	44	.Ft void *
2d21ac55 A	45	.Fo mmap
	46	.Fa "void *addr"
	47	.Fa "size_t len"
	48	.Fa "int prot"
	49	.Fa "int flags"
	50	.Fa "int fildes"
	51	.Fa "off_t offset"
	52	.Fc
9bccf70c A	53	.Sh DESCRIPTION
	54	The
	55	.Nm mmap
	56	function causes the pages starting at
	57	.Fa addr
	58	and continuing for at most
	59	.Fa len
	60	bytes to be mapped from the object described by
2d21ac55	61	.Fa fildes ,
9bccf70c A	62	starting at byte offset
	63	.Fa offset .
	64	If
	65	.Fa offset
	66	or
	67	.Fa len
	68	is not a multiple of the pagesize, the mapped region may extend past the
	69	specified range.
	70	.Pp
	71	If
	72	.Fa addr
	73	is non-zero, it is used as a hint to the system.
	74	(As a convenience to the system, the actual address of the region may differ
	75	from the address supplied.)
	76	If
	77	.Fa addr
	78	is zero, an address will be selected by the system.
	79	The actual starting address of the region is returned.
	80	A successful
	81	.Fa mmap
	82	deletes any previous mapping in the allocated address range.
	83	.Pp
	84	The protections (region accessibility) are specified in the
	85	.Fa prot
	86	argument by
	87	.Em or Ns 'ing
	88	the following values:
	89	.Pp
	90	.Bl -tag -width MAP_FIXEDX
	91	.It Dv PROT_EXEC
	92	Pages may be executed.
	93	.It Dv PROT_READ
	94	Pages may be read.
	95	.It Dv PROT_WRITE
	96	Pages may be written.
	97	.El
	98	.Pp
	99	The
	100	.Fa flags
2d21ac55 A	101	parameter specifies the type of the mapped object, mapping options,
	102	and whether modifications made to the mapped copy of the page
	103	are private to the process (copy-on-write)
	104	or are to be shared with other references.
	105	Sharing, mapping type, and options are specified in the
9bccf70c A	106	.Fa flags
	107	argument by
	108	.Em or Ns 'ing
	109	the following values:
	110	.Pp
2d21ac55	111	.Bl -tag -width MAP_HASSEMAPHOREX
9bccf70c A	112	.It Dv MAP_ANON
9bccf70c A	113	Map anonymous memory not associated with any specific file.
2d21ac55	114	Mac OS X specific: the file descriptor used for creating
9bccf70c	115	.Dv MAP_ANON
2d21ac55 A	116	regions can be used to pass some Mach VM flags, and can
	117	be specified as \-1 if no such flags are associated with
	118	the region. Mach VM flags are defined in
	119	<mach/vm_statistics.h> and the ones that currently apply
	120	to
	121	.Nm mmap
	122	are:
	123	.Pp
	124	VM_FLAGS_PURGABLE to create Mach purgable (i.e. volatile) memory
	125	VM_MAKE_TAG(tag) to associate an 8-bit tag with the region
	126	.Pp
	127	<mach/vm_statistics.h> defines some preset tags (with a VM_MEMORY_ prefix).
	128	Users are encouraged to use tags between 240 and 255.
	129	Tags are used by tools such as vmmap(1) to help identify specific memory regions.
9bccf70c A	130	.It Dv MAP_FILE
	131	Mapped from a regular file or character-special device memory. (This is
	132	the default mapping type, and need not be specified.)
	133	.It Dv MAP_FIXED
	134	Do not permit the system to select a different address than the one
	135	specified.
	136	If the specified address cannot be used,
	137	.Nm mmap
	138	will fail.
	139	If MAP_FIXED is specified,
	140	.Fa addr
	141	must be a multiple of the pagesize.
	142	Use of this option is discouraged.
	143	.It Dv MAP_HASSEMAPHORE
	144	Notify the kernel that the region may contain semaphores and that special
	145	handling may be necessary.
9bccf70c	146	.It Dv MAP_PRIVATE
2d21ac55	147	Modifications are private (copy-on-write).
9bccf70c A	148	.It Dv MAP_SHARED
9bccf70c A	149	Modifications are shared.
2d21ac55 A	150	.It Dv MAP_NOCACHE
	151	Pages in this mapping are not retained in the kernel's memory cache.
	152	If the system runs low on memory, pages in MAP_NOCACHE mappings will be among
	153	the first to be reclaimed.
	154	This flag is intended for mappings that have little locality and
	155	provides a hint to the kernel that pages in this mapping are unlikely to be needed
	156	again in the near future.
9bccf70c A	157	.El
9bccf70c A	158	.Pp
2d21ac55 A	159	Conforming applications must specify either MAP_PRIVATE or MAP_SHARED.
2d21ac55 A	160	.Pp
9bccf70c A	161	The
	162	.Xr close 2
	163	function does not unmap pages, see
	164	.Xr munmap 2
	165	for further information.
	166	.Pp
	167	The current design does not allow a process to specify the location of
	168	swap space.
	169	In the future we may define an additional mapping type,
	170	.Dv MAP_SWAP ,
	171	in which
	172	the file descriptor argument specifies a file or device to which swapping
	173	should be done.
	174	.Sh RETURN VALUES
	175	Upon successful completion,
	176	.Nm mmap
	177	returns a pointer to the mapped region.
	178	Otherwise, a value of -1 is returned and
	179	.Va errno
	180	is set to indicate the error.
	181	.Sh ERRORS
	182	.Fn Mmap
	183	will fail if:
	184	.Bl -tag -width Er
2d21ac55 A	185	.\" ===========
	186	.It Bq Er EACCES
	187	.Fa Fildes
	188	is not open for reading.
	189	.\" ===========
9bccf70c	190	.It Bq Er EACCES
9bccf70c A	191	The flags
	192	.Dv PROT_WRITE
	193	and
	194	.Dv MAP_SHARED
2d21ac55	195	are specified as part of the
9bccf70c A	196	.Fa flags
	197	and
	198	.Fa prot
	199	parameters and
2d21ac55 A	200	.Fa fildes
	201	is not open for writing.
	202	.\" ===========
9bccf70c	203	.It Bq Er EBADF
2d21ac55 A	204	.Fa fildes
2d21ac55 A	205	is not a valid file descriptor for an open file.
9bccf70c A	206	.It Bq Er EINVAL
9bccf70c A	207	.Dv MAP_FIXED
2d21ac55	208	is specified and the
9bccf70c	209	.I addr
2d21ac55 A	210	parameter is not page aligned.
	211	.\" ===========
	212	.It Bq Er EINVAL
	213	.Fa fildes
	214	does not reference a regular or character special file.
	215	.\" ===========
	216	.It Bq Er EINVAL
	217	.Fa flags
	218	does not include either MAP_PRIVATE or MAP_SHARED.
	219	.\" ===========
	220	.It Bq Er EINVAL
	221	.Fa len
	222	is not greater than zero.
	223	.\" ===========
	224	.It Bq Er EINVAL
	225	.Fa offset
	226	is not a multiple of the page size,
	227	as returned by
	228	.Xr sysconf 3 .
	229	.\" ===========
	230	.It Bq Er EMFILE
	231	The limit on mapped regions (per process or system) is exceeded.
	232	.\" ===========
	233	.It Bq Er ENODEV
	234	The file type for
	235	.Fa fildes
	236	is not supported for mapping.
	237	.\" ===========
	238	.It Bq Er ENOMEM
	239	.Dv MAP_FIXED
	240	is specified and the address range specified
	241	exceeds the address space limit for the process.
	242	.\" ===========
9bccf70c A	243	.It Bq Er ENOMEM
9bccf70c A	244	.Dv MAP_FIXED
2d21ac55	245	is specified and the address specified by the
9bccf70c	246	.Fa addr
2d21ac55 A	247	parameter isn't available.
	248	.\" ===========
	249	.It Bq Er ENOMEM
9bccf70c	250	.Dv MAP_ANON
2d21ac55 A	251	is specified and insufficient memory is available.
	252	.\" ===========
	253	.It Bq Er ENXIO
	254	Addresses in the specified range are invalid for fildes.
	255	.\" ===========
	256	.It Bq Er EOVERFLOW
	257	Addresses in the specified range exceed the maximum offset
	258	set for fildes.
	259	.El
	260	.Sh LEGACY SYNOPSIS
	261	.Fd #include <sys/types.h>
	262	.Fd #include <sys/mman.h>
	263	.Pp
	264	The include file
	265	.In sys/types.h
	266	is necessary.
	267	.Sh COMPATIBILITY
	268	.Fn mmap
	269	now returns with
	270	.Va errno
	271	set to EINVAL in places that historically succeeded.
	272	The rules have changed as follows:
	273	.Bl -bullet
	274	.It
	275	The
	276	.Fa flags
	277	parameter must specify either MAP_PRIVATE or MAP_SHARED.
	278	.It
	279	The
	280	.Fa size
	281	parameter must not be 0.
	282	.It
	283	The
	284	.Fa off
	285	parameter must be a multiple of pagesize,
	286	as returned by
	287	.Fn sysconf .
9bccf70c A	288	.El
	289	.Sh "SEE ALSO"
	290	.Xr getpagesize 2 ,
9bccf70c A	291	.Xr madvise 2 ,
9bccf70c A	292	.Xr mincore 2 ,
2d21ac55 A	293	.Xr mlock 2 ,
	294	.Xr mprotect 2 ,
	295	.Xr msync 2 ,
	296	.Xr munmap 2 ,
	297	.Xr sysconf 3 ,
	298	.Xr compat 5