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Eric Estievenart <eric.estievenart@free.fr>
Note that MAP_FIXED replaces existing mappings
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Michael Kerrisk
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man2/mmap.2
41
man2/mmap.2
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@ -30,8 +30,10 @@
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.\" MAP_LOCKED works from 2.5.37
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.\" Modified 2004-06-17 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Modified 2004-09-11 by aeb
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.\" Modified 2004-12-08, from Eric Estievenart <eric.estievenart@free.fr>
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.\" Modified 2004-12-08, mtk, formatting tidy-ups
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.\"
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.TH MMAP 2 2004-09-11 "Linux 2.6.7" "Linux Programmer's Manual"
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.TH MMAP 2 2004-12-08 "Linux 2.6.9" "Linux Programmer's Manual"
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.SH NAME
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mmap, munmap \- map or unmap files or devices into memory
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.SH SYNOPSIS
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@ -43,7 +45,7 @@ mmap, munmap \- map or unmap files or devices into memory
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.BI "int munmap(void *" start ", size_t " length );
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.SH DESCRIPTION
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The
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.B mmap
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.BR mmap ()
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function asks to map
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.I length
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bytes starting at offset
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@ -54,7 +56,7 @@ into memory, preferably at address
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.IR start .
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This latter address is a hint only, and is usually specified as 0.
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The actual place where the object is mapped is returned by
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.BR mmap ,
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.BR mmap (),
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and is never 0.
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.LP
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The
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@ -84,9 +86,16 @@ the process or are to be shared with other references. It has bits
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.TP 1.1i
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.B MAP_FIXED
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Do not select a different address than the one specified.
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If the memory region specified by
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.B start
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and
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.B len
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overlaps pages of any existing mapping(s), then the overlapped
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part of the existing mapping(s) will be discarded.
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If the specified address cannot be used,
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.B mmap
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will fail. If MAP_FIXED is specified,
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.BR mmap ()
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will fail.
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If MAP_FIXED is specified,
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.I start
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must be a multiple of the pagesize. Use of this option is discouraged.
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.TP
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@ -103,7 +112,7 @@ are called.
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Create a private copy-on-write mapping.
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Stores to the region do not affect the original file.
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It is unspecified whether changes made to the file after the
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.B mmap
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.BR mmap ()
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call are visible in the mapped region.
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.LP
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You must specify exactly one of MAP_SHARED and MAP_PRIVATE.
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@ -134,7 +143,7 @@ when no memory is available.
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.TP
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.BR MAP_LOCKED " (since Linux 2.5.37)"
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Lock the pages of the mapped region into memory in the manner of
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.BR mlock() .
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.BR mlock () .
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This flag is ignored in older kernels.
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.\" If set, the mapped pages will not be swapped out.
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.TP
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@ -180,7 +189,7 @@ should be a multiple of the page size as returned by
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.BR getpagesize (2).
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.LP
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Memory mapped by
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.B mmap
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.BR mmap ()
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is preserved across
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.BR fork (2),
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with the same attributes.
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@ -192,7 +201,7 @@ changing the size of the underlying file of a mapping on the pages that
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correspond to added or removed regions of the file is unspecified.
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The
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.B munmap
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.BR munmap ()
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system call deletes the mappings for the specified address range, and
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causes further references to addresses within the range to generate
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invalid memory references. The region is also automatically unmapped
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@ -209,7 +218,7 @@ indicated range does not contain any mapped pages.
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For file-backed mappings, the
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.B st_atime
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field for the mapped file may be updated at any time between the
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.B mmap()
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.BR mmap ()
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and the corresponding unmapping; the first reference to a mapped
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page will update the field if it has not been already.
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.LP
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@ -219,11 +228,11 @@ and
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.B st_mtime
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field for a file mapped with PROT_WRITE and MAP_SHARED will be updated after
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a write to the mapped region, and before a subsequent
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.I msync()
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.BR msync ()
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with the MS_SYNC or MS_ASYNC flag, if one occurs.
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.SH "RETURN VALUE"
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On success,
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.B mmap
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.BR mmap ()
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returns a pointer to the mapped area.
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On error, the value
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.B MAP_FAILED
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@ -231,7 +240,7 @@ On error, the value
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.I errno
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is set appropriately.
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On success,
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.B munmap
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.BR munmap ()
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returns 0, on failure \-1, and
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.I errno
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is set (probably to EINVAL).
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@ -314,10 +323,10 @@ to the file (for example, beyond the end of the file, including the
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case where another process has truncated the file).
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.SH AVAILABILITY
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On POSIX systems on which
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.BR mmap ,
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.B msync
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.BR mmap (),
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.BR msync ()
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and
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.B munmap
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.BR munmap ()
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are available,
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.B _POSIX_MAPPED_FILES
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is defined in <unistd.h> to a value greater than 0. (See also
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