1.\" $OpenBSD: mmap.2,v 1.37 2008/06/30 05:46:46 otto Exp $ 2.\" $NetBSD: mmap.2,v 1.5 1995/06/24 10:48:59 cgd Exp $ 3.\" 4.\" Copyright (c) 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)mmap.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: June 30 2008 $ 34.Dt MMAP 2 35.Os 36.Sh NAME 37.Nm mmap 38.Nd map files or devices into memory 39.Sh SYNOPSIS 40.Fd #include <sys/types.h> 41.Fd #include <sys/mman.h> 42.Ft void * 43.Fn mmap "void *addr" "size_t len" "int prot" "int flags" "int fd" "off_t offset" 44.Sh DESCRIPTION 45The 46.Nm mmap 47function causes the pages starting at 48.Fa addr 49and continuing for at most 50.Fa len 51bytes to be mapped from the object described by 52.Fa fd , 53starting at byte offset 54.Fa offset . 55If 56.Fa offset 57or 58.Fa len 59is not a multiple of the pagesize, the mapped region may extend past the 60specified range. 61.Pp 62If 63.Fa addr 64is non-zero, it is used as a hint to the system. 65(As a convenience to the system, the actual address of the region may differ 66from the address supplied.) 67If 68.Fa addr 69is zero, an address will be selected by the system. 70The actual starting address of the region is returned. 71A successful 72.Fa mmap 73deletes any previous mapping in the allocated address range. 74.Pp 75The protections (region accessibility) are specified in the 76.Fa prot 77argument by OR'ing the following values: 78.Pp 79.Bl -tag -width "PROT_WRITE " -offset indent -compact 80.It Dv PROT_EXEC 81Pages may be executed. 82.It Dv PROT_READ 83Pages may be read. 84.It Dv PROT_WRITE 85Pages may be written. 86.It Dv PROT_NONE 87No permissions. 88.El 89.Pp 90The 91.Fa flags 92parameter specifies the type of the mapped object, mapping options, and 93whether modifications made to the mapped copy of the page are private 94to the process or are to be shared with other references. 95Sharing, mapping type, and options are specified in the 96.Fa flags 97argument by OR'ing the following values: 98.Bl -tag -width MAP_FIXEDX 99.It Dv MAP_ANON 100Map anonymous memory not associated with any specific file. 101The file descriptor used for creating 102.Dv MAP_ANON 103must currently be \-1 indicating no name is associated with the 104region. 105.It Dv MAP_FILE 106Mapped from a regular file or character-special device memory. 107(This is the default mapping type, and need not be specified.) 108.It Dv MAP_FIXED 109Do not permit the system to select a different address than the one 110specified. 111If the specified address cannot be used, 112.Nm mmap 113will fail. 114If 115.Dv MAP_FIXED 116is specified, 117.Fa addr 118must be a multiple of the pagesize. 119Use of this option is discouraged. 120.It Dv MAP_HASSEMAPHORE 121Notify the kernel that the region may contain semaphores and that special 122handling may be necessary. 123.It Dv MAP_INHERIT 124Permit regions to be inherited across 125.Xr exec 3 126system calls. 127.It Dv MAP_PRIVATE 128Modifications are private. 129.It Dv MAP_SHARED 130Modifications are shared. 131.It Dv MAP_COPY 132Modifications are private and, unlike 133.Dv MAP_PRIVATE , 134modifications made by others are not visible. 135This option is deprecated, shouldn't be used and behaves just like 136.Dv MAP_PRIVATE 137in the current implementation. 138.El 139.Pp 140The 141.Xr close 2 142function does not unmap pages; see 143.Xr munmap 2 144for further information. 145.Pp 146The current design does not allow a process to specify the location of 147swap space. 148In the future we may define an additional mapping type, 149.Dv MAP_SWAP , 150in which 151the file descriptor argument specifies a file or device to which swapping 152should be done. 153.Sh RETURN VALUES 154Upon successful completion, 155.Nm mmap 156returns a pointer to the mapped region. 157Otherwise, a value of 158.Dv MAP_FAILED 159is returned and 160.Va errno 161is set to indicate the error. 162The symbol 163.Dv MAP_FAILED 164is defined in the header 165.Ao Pa sys/mman.h Ac . 166No successful return from 167.Fn mmap 168will return the value 169.Dv MAP_FAILED . 170.Sh ERRORS 171.Fn mmap 172will fail if: 173.Bl -tag -width Er 174.It Bq Er EACCES 175The flag 176.Dv PROT_READ 177was specified as part of the 178.Fa prot 179parameter and 180.Fa fd 181was not open for reading. 182The flags 183.Dv MAP_SHARED 184and 185.Dv PROT_WRITE 186were specified as part 187of the 188.Fa flags 189and 190.Fa prot 191parameters and 192.Fa fd 193was not open for writing. 194.It Bq Er EBADF 195.Fa fd 196is not a valid open file descriptor. 197.It Bq Er EINVAL 198.Dv MAP_FIXED 199was specified and the 200.Fa addr 201parameter was not page aligned or 202.Fa addr 203and 204.Fa size 205specify a region that would extend beyond the end of the address space. 206.Fa fd 207did not reference a regular or character special file. 208.It Bq Er ENOMEM 209.Dv MAP_FIXED 210was specified and the 211.Fa addr 212parameter wasn't available. 213.Dv MAP_ANON 214was specified and insufficient memory was available. 215.El 216.Sh SEE ALSO 217.Xr madvise 2 , 218.Xr mincore 2 , 219.Xr mlock 2 , 220.Xr mprotect 2 , 221.Xr mquery 2 , 222.Xr msync 2 , 223.Xr munmap 2 , 224.Xr getpagesize 3 225.Sh BUGS 226Due to a limitation of the current vm system (see 227.Xr uvm 9 ) , 228mapping descriptors 229.Dv PROT_WRITE 230without also specifying 231.Dv PROT_READ 232is useless 233(results in a segmentation fault when first accessing the mapping). 234This means that such descriptors must be opened with 235.Dv O_RDWR , 236which requires both read and write permissions on the underlying 237object. 238