.\" $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