271 lines
6.9 KiB
Groff
271 lines
6.9 KiB
Groff
.\" $NetBSD: mmap.2,v 1.24 2001/10/23 02:10:23 mycroft Exp $
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.\"
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.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mmap.2 8.4 (Berkeley) 5/11/95
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.\"
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.Dd May 11, 1995
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.Dt MMAP 2
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.Os
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.Sh NAME
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.Nm mmap
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.Nd map files or devices into memory
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <sys/mman.h>
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.Ft void *
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.Fn mmap "void *addr" "size_t len" "int prot" "int flags" "int fd" "off_t offset"
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.Sh DESCRIPTION
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The
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.Nm mmap
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function causes the pages starting at
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.Fa addr
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and continuing for at most
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.Fa len
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bytes to be mapped from the object described by
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.Fa fd ,
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starting at byte offset
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.Fa offset .
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If
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.Fa len
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is not a multiple of the pagesize, the mapped region may extend past the
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specified range.
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Any such extension beyond the end of the mapped object will be zero-filled.
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.Pp
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If
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.Fa addr
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is non-zero, it is used as a hint to the system.
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(As a convenience to the system, the actual address of the region may differ
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from the address supplied.)
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If
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.Fa addr
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is zero, an address will be selected by the system.
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The actual starting address of the region is returned.
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A successful
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.Fa mmap
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deletes any previous mapping in the allocated address range.
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.Pp
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The protections (region accessibility) are specified in the
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.Fa prot
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argument by
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.Em or Ns 'ing
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the following values:
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.Pp
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.Bl -tag -width MAP_FIXEDX
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.It Dv PROT_EXEC
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Pages may be executed.
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.It Dv PROT_READ
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Pages may be read.
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.It Dv PROT_WRITE
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Pages may be written.
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.It Dv PROT_NONE
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Pages may not be accessed.
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.El
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.Pp
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.Bf -symbolic
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Note that, due to hardware limitations, on some platforms
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.Dv PROT_WRITE
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may imply
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.Dv PROT_READ ,
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and
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.Dv PROT_READ
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may imply
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.Dv PROT_EXEC .
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Portable programs should not rely on these flags being separately
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enforcable.
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.Ef
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.Pp
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The
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.Fa flags
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parameter specifies the type of the mapped object, mapping options and
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whether modifications made to the mapped copy of the page are private
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to the process or are to be shared with other references.
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Note that either
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.Dv MAP_SHARED ,
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.Dv MAP_PRIVATE
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or
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.Dv MAP_COPY
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must be specified.
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Sharing, mapping type and options are specified in the
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.Fa flags
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argument by
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.Em or Ns 'ing
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the following values:
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.Pp
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.Bl -tag -width MAP_FIXEDX
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.It Dv MAP_ANON
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Map anonymous memory not associated with any specific file.
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The file descriptor used for creating
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.Dv MAP_ANON
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regions is used only for
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naming, and may be specified as \-1 if no name is associated with the
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region.
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.It Dv MAP_FILE
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Mapped from a regular file or character-special device memory.
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.It Dv MAP_FIXED
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Do not permit the system to select a different address than the one
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specified.
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If the specified address cannot be used,
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.Nm mmap
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will fail.
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If MAP_FIXED is specified,
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.Fa addr
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must be a multiple of the pagesize.
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Use of this option is discouraged.
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.It Dv MAP_HASSEMAPHORE
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Notify the kernel that the region may contain semaphores and that special
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handling may be necessary.
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.It Dv MAP_INHERIT
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Permit regions to be inherited across
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.Xr execve 2
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system calls.
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.It Dv MAP_PRIVATE
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Modifications made by this process are private, however modifications made by
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other processes using
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.Dv MAP_SHARED
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will be seen.
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.It Dv MAP_SHARED
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Modifications are shared.
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.It Dv MAP_COPY
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Modifications are private, including other processes.
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.El
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.Pp
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The
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.Xr close 2
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function does not unmap pages, see
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.Xr munmap 2
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for further information.
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.Pp
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The current design does not allow a process to specify the location of
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swap space.
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In the future we may define an additional mapping type,
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.Dv MAP_SWAP ,
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in which
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the file descriptor argument specifies a file or device to which swapping
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should be done.
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.Sh RETURN VALUES
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Upon successful completion,
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.Nm mmap
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returns a pointer to the mapped region.
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Otherwise, a value of
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.Dv MAP_FAILED
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is returned and
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.Va errno
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is set to indicate the error.
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The symbol
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.Dv MAP_FAILED
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is defined in the header
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.Ao Pa sys/mman.h Ac .
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No successful return from
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.Fn mmap
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will return the value
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.Dv MAP_FAILED .
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.Sh ERRORS
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.Fn mmap
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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The flag
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.Dv PROT_READ
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was specified as part of the
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.Fa prot
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parameter and
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.Fa fd
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was not open for reading.
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The flags
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.Dv MAP_SHARED
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and
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.Dv PROT_WRITE
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were specified as part of the
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.Fa flags
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and
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.Fa prot
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parameters and
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.Fa fd
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was not open for writing.
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.It Bq Er EBADF
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.Fa fd
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is not a valid open file descriptor.
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.It Bq Er EINVAL
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.\"One of
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.\".Dv MAP_ANON
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.\"or
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.\".Dv MAP_FILE
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.\"was not specified as part of the
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.\".Fa flags
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.\"parameter.
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.Dv MAP_FIXED
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was specified and the
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.Fa addr
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parameter was not page aligned or was outside of the
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valid address range for a process.
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.Dv MAP_ANON was specified and
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.Fa fd
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was not \-1.
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.Fa len
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was less than zero.
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.It Bq Er ENODEV
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.Fa fd
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did not reference a regular or character special file.
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.It Bq Er ENOMEM
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.Dv MAP_FIXED
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was specified and the
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.Fa addr
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parameter wasn't available.
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.Dv MAP_ANON
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was specified and insufficient memory was available.
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.It Bq Er EOVERFLOW
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.Fa fd
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references a regular file and the value of
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.Fa offset
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plus
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.Fa len
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would exceed the offset maximum established in its open file description.
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.El
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.Sh SEE ALSO
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.Xr madvise 2 ,
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.Xr mincore 2 ,
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.Xr mlock 2 ,
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.Xr mprotect 2 ,
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.Xr msync 2 ,
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.Xr munmap 2 ,
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.Xr getpagesize 3
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.Sh BUGS
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The
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.Dv MAP_COPY
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flag is not implemented. The current
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.Dv MAP_COPY
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semantics are the same as those of the
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.Dv MAP_PRIVATE
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flag.
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