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Place MAP_* flags list in alphabeitical order.
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Michael Kerrisk
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133
man2/mmap.2
133
man2/mmap.2
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@ -134,65 +134,13 @@ Both of these flags are described in POSIX.1-2001.
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In addition, zero or more of the following values can be ORed in
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.IR flags :
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.\" FIXME ? Place the following list in alphabetical order?
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.TP
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.B MAP_32BIT
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Put the mapping into the first 2GB of the process address space.
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Ignored when
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.B MAP_FIXED
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Don't interpret
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.I start
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as a hint: place the mapping at exactly that address.
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.I start
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must be a multiple of the page size.
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If the memory region specified by
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.I start
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and
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.I 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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.BR mmap ()
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will fail.
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Because requiring a fixed address for a mapping is less portable,
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the use of this option is discouraged.
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.TP
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.B MAP_DENYWRITE
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This flag is ignored.
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.\" Introduced in 1.1.36, removed in 1.3.24.
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(Long ago, it signalled that attempts to write to the underlying file
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should fail with
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.BR ETXTBUSY .
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But this was a source of denial-of-service attacks.)
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.TP
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.B MAP_EXECUTABLE
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This flag is ignored.
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.\" Introduced in 1.1.38, removed in 1.3.24. Flag tested in proc_follow_link.
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.\" (Long ago, it signalled that the underlying file is an executable.
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.\" However, that information was not really used anywhere.)
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.\" Linus talked about DOS related to MAP_EXECUTABLE, but he was thinking of
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.\" MAP_DENYWRITE?
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.TP
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.B MAP_NORESERVE
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Do not reserve swap space for this mapping.
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When swap space is reserved, one has the guarantee
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that it is possible to modify the mapping.
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When swap space is not reserved one might get SIGSEGV upon a write
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if no physical memory is available.
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See also the discussion of the file
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.I /proc/sys/vm/overcommit_memory
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in
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.BR proc (5).
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In kernels before 2.6, this flag only had effect for
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private writable mappings.
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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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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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.B MAP_GROWSDOWN
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Used for stacks.
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Indicates to the kernel virtual memory system that the mapping
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should extend downwards in memory.
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is set.
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This flag is currently only supported on x86-64 for 64bit programs.
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.TP
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.B MAP_ANON
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Synonym for
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@ -221,21 +169,56 @@ in conjunction with
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.B MAP_SHARED
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is only supported on Linux since kernel 2.4.
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.TP
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.B MAP_DENYWRITE
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This flag is ignored.
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.\" Introduced in 1.1.36, removed in 1.3.24.
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(Long ago, it signalled that attempts to write to the underlying file
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should fail with
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.BR ETXTBUSY .
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But this was a source of denial-of-service attacks.)
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.TP
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.B MAP_EXECUTABLE
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This flag is ignored.
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.\" Introduced in 1.1.38, removed in 1.3.24. Flag tested in proc_follow_link.
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.\" (Long ago, it signalled that the underlying file is an executable.
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.\" However, that information was not really used anywhere.)
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.\" Linus talked about DOS related to MAP_EXECUTABLE, but he was thinking of
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.\" MAP_DENYWRITE?
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.TP
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.B MAP_FILE
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Compatibility flag.
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Ignored.
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.\" On some systems, this was required as the opposite of
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.\" MAP_ANONYMOUS -- mtk, 1 May 2007
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.TP
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.B MAP_32BIT
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Put the mapping into the first 2GB of the process address space.
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Ignored when
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.B MAP_FIXED
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is set.
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This flag is currently only supported on x86-64 for 64bit programs.
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Don't interpret
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.I start
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as a hint: place the mapping at exactly that address.
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.I start
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must be a multiple of the page size.
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If the memory region specified by
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.I start
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and
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.I 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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.BR mmap ()
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will fail.
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Because requiring a fixed address for a mapping is less portable,
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the use of this option is discouraged.
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.TP
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.BR MAP_POPULATE " (since Linux 2.5.46)"
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Populate (prefault) page tables for a file mapping,
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by performing read-ahead on the file.
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Later accesses to the mapping will not be blocked by page faults.
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.B MAP_GROWSDOWN
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Used for stacks.
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Indicates to the kernel virtual memory system that the mapping
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should extend downwards in memory.
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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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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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.BR MAP_NONBLOCK " (since Linux 2.5.46)"
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Only meaningful in conjunction with
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@ -243,6 +226,24 @@ Only meaningful in conjunction with
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Don't perform read-ahead:
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only create page tables entries for pages
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that are already present in RAM.
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.TP
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.B MAP_NORESERVE
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Do not reserve swap space for this mapping.
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When swap space is reserved, one has the guarantee
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that it is possible to modify the mapping.
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When swap space is not reserved one might get SIGSEGV upon a write
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if no physical memory is available.
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See also the discussion of the file
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.I /proc/sys/vm/overcommit_memory
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in
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.BR proc (5).
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In kernels before 2.6, this flag only had effect for
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private writable mappings.
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.TP
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.BR MAP_POPULATE " (since Linux 2.5.46)"
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Populate (prefault) page tables for a file mapping,
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by performing read-ahead on the file.
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Later accesses to the mapping will not be blocked by page faults.
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.LP
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Of the above flags, only
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.B MAP_FIXED
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