e1f4e80c88
in the main text of various man pages. Thanks to Warner Losh for adding an option to manck to allow it to scan the entire man page looking for bogus xrefs, instead of just checking the SEE ALSO section.
229 lines
6.4 KiB
Groff
229 lines
6.4 KiB
Groff
.\" 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 8.1 (Berkeley) 6/4/93
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.\"
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.Dd "June 4, 1993"
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.Dt MMAP 2
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.Os BSD 4
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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 SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/mman.h>
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.Ft caddr_t
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.Fn mmap "caddr_t 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 offset
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or
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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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.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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.El
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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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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 are private.
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.It Dv MAP_SHARED
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Modifications are shared.
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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 -1 is returned and
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.Va errno
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is set to indicate the error.
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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 PROT_WRITE ,
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.Dv MAP_SHARED
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and
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.Dv MAP_WRITE
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were specified as part
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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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.I addr
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parameter was not page aligned.
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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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.Sh "SEE ALSO"
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.Xr msync 2 ,
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.Xr munmap 2 ,
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.Xr mprotect 2 ,
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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 munlock 2 ,
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.Xr getpagesize 3
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.Sh BUGS
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.Ar len
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is limit to 2GB. Mmapping slightly more than 2GB doesn't work, but
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mapping a window of size (filesize % 2GB) for file sizes of slightly
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less than 2G, 4GB, 6GB and 8GB.
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The limit is imposed for a variety of reasons. Most of them have to do
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with FreeBSD not wanting to use 64 bit offsets in the VM system due to
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the extreme performance penalty. So FreeBSD use 32bit page indexes and
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this gives FreeBSD a maximum of 8TB filesizes. It's actually bugs in
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the filesystem code that causes the limit to be further restricted to
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1TB (loss of precision when doing blockno calculations).
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Another reason for the 2GB limit is that filesystem metadata can
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reside at negative offsets.
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