.\" $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/types.h> .Fd #include <sys/mman.h> .Ft void * .Fn mmap "void *addr" "size_t len" "int prot" "int flags" "int fd" "off_t offset" .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 fd , 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 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_FIXEDX .It Dv MAP_ANON Map anonymous memory not associated with any specific file. The file descriptor 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. .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_INHERIT Permit regions to be inherited across .Xr exec 2 system calls. .It Dv MAP_PRIVATE Modifications are private. .It Dv MAP_SHARED Modifications are shared. .El .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 The flag .Dv PROT_READ was specified as part of the .Fa prot parameter and .Fa fd was not open for reading. The flags .Dv PROT_WRITE and .Dv MAP_SHARED were specified as part of the .Fa flags and .Fa prot parameters and .Fa fd was not open for writing. .It Bq Er EBADF .Fa fd is not a valid open file descriptor. .It Bq Er EINVAL .Dv MAP_FIXED was specified and the .I addr parameter was not page aligned. .Fa fd did not reference a regular or character special file. .It Bq Er ENOMEM .Dv MAP_FIXED was specified and the .Fa addr parameter wasn't available. .Dv MAP_ANON was specified and insufficient memory was available. .El .Sh "SEE ALSO" .Xr getpagesize 2 , .Xr msync 2 , .Xr munmap 2 , .Xr mprotect 2 , .Xr madvise 2 , .Xr mincore 2 , .Xr mlock 2