The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
Copyright © 2001-2024 The IEEE and The Open Group

NAME

sys/mman.h — memory management declarations

SYNOPSIS

#include <sys/mman.h>

DESCRIPTION

The <sys/mman.h> header shall define the following symbolic constants for use as protection options:

PROT_EXEC
Page can be executed.
PROT_NONE
Page cannot be accessed.
PROT_READ
Page can be read.
PROT_WRITE
Page can be written.

The <sys/mman.h> header shall define the following symbolic constants for use as flag options:

MAP_ANON
Synonym for MAP_ANONYMOUS. MAP_ANON shall have the same value as MAP_ANONYMOUS.
MAP_ANONYMOUS
Map anonymous memory.
MAP_FIXED
Interpret addr exactly.
MAP_PRIVATE
Changes are private.
MAP_SHARED
Share changes.

[XSI|SIO] [Option Start] The <sys/mman.h> header shall define the following symbolic constants for the msync() function:

MS_ASYNC
Perform asynchronous writes.
MS_INVALIDATE
Invalidate mappings.
MS_SYNC
Perform synchronous writes.
[Option End]

[ML] [Option Start] The <sys/mman.h> header shall define the following symbolic constants for the mlockall() function:

MCL_CURRENT
Lock currently mapped pages.
MCL_FUTURE
Lock pages that become mapped.
[Option End]

The <sys/mman.h> header shall define the symbolic constant MAP_FAILED which shall have type void * and shall be used to indicate a failure from the mmap() function .

[ADV] [Option Start] If the Advisory Information option is supported, the <sys/mman.h> header shall define symbolic constants for the advice argument to the posix_madvise() function as follows:

POSIX_MADV_DONTNEED

The application expects that it will not access the specified range in the near future.
POSIX_MADV_NORMAL

The application has no advice to give on its behavior with respect to the specified range. It is the default characteristic if no advice is given for a range of memory.
POSIX_MADV_RANDOM

The application expects to access the specified range in a random order.
POSIX_MADV_SEQUENTIAL

The application expects to access the specified range sequentially from lower addresses to higher addresses.
POSIX_MADV_WILLNEED

The application expects to access the specified range in the near future.
[Option End]

[TYM] [Option Start] The <sys/mman.h> header shall define the following symbolic constants for use as flags for the posix_typed_mem_open() function:

POSIX_TYPED_MEM_ALLOCATE

Allocate on mmap().
POSIX_TYPED_MEM_ALLOCATE_CONTIG

Allocate contiguously on mmap().
POSIX_TYPED_MEM_MAP_ALLOCATABLE

Map on mmap(), without affecting allocatability.
[Option End]

The <sys/mman.h> header shall define the mode_t, off_t, and size_t types as described in <sys/types.h> .

[TYM] [Option Start] The <sys/mman.h> header shall define the posix_typed_mem_info structure, which shall include at least the following member:

size_t  posix_tmi_length  Maximum length which may be allocated
                          from a typed memory object.
[Option End]

The <sys/mman.h> header shall define the following symbolic constants as described in <fcntl.h>:


[SHM|TYM] [Option Start]
O_RDONLY
O_RDWR
[Option End]
[TYM] [Option Start]
O_WRONLY
O_CLOEXEC
O_CLOFORK
[Option End]
[SHM] [Option Start]
O_CREAT
O_EXCL
O_TRUNC
[Option End]

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

[MLR][Option Start]
int    mlock(const void *, size_t);
[Option End]
[ML][Option Start]
int    mlockall(int);
[Option End]
void  *mmap(void *, size_t, int, int, int, off_t);
int    mprotect(void *, size_t, int);
[XSI|SIO][Option Start]
int    msync(void *, size_t, int);
[Option End]
[MLR][Option Start]
int    munlock(const void *, size_t);
[Option End]
[ML][Option Start]
int    munlockall(void);
[Option End]
int    munmap(void *, size_t);
[ADV][Option Start]
int    posix_madvise(void *, size_t, int);
[Option End]
[TYM][Option Start]
int    posix_mem_offset(const void *restrict, size_t, off_t *restrict,
           size_t *restrict, int *restrict);
int    posix_typed_mem_get_info(int, struct posix_typed_mem_info *);
int    posix_typed_mem_open(const char *, int, int);
[Option End]
[SHM][Option Start]
int    shm_open(const char *, int, mode_t);
int    shm_unlink(const char *);
[Option End]

Inclusion of the <sys/mman.h> header may make visible all symbols from the <fcntl.h> header.


The following sections are informative.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

<sys/types.h>

XSH mlock , mlockall , mmap , mprotect , msync , munmap , posix_madvise , posix_mem_offset , posix_typed_mem_get_info , posix_typed_mem_open , shm_open , shm_unlink

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 5

Updated for alignment with the POSIX Realtime Extension.

Issue 6

The <sys/mman.h> header is marked as dependent on support for either the Memory Mapped Files, Process Memory Locking, or Shared Memory Objects options.

The following changes are made for alignment with IEEE Std 1003.1j-2000:

The restrict keyword is added to the prototype for posix_mem_offset().

IEEE PASC Interpretation 1003.1 #102 is applied, adding the prototype for posix_madvise().

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/16 is applied, correcting margin code and shading errors for the mlock() and munlock() functions.

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/34 is applied, changing the margin code for the mmap() function from MF|SHM to MC3 (notation for MF|SHM|TYM).

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/36 is applied, changing the margin code for the munmap() function from MF|SHM to MC3 (notation for MF|SHM|TYM).

Issue 7

SD5-XBD-ERN-5 is applied, rewriting the DESCRIPTION.

Functionality relating to the Memory Protection and Memory Mapped Files options is moved to the Base.

This reference page is clarified with respect to macros and symbolic constants.

Issue 8

Austin Group Defect 593 is applied, adding O_RDONLY, O_RDWR, O_WRONLY, O_CLOEXEC, O_CLOFORK, O_CREAT, O_EXCL, and O_TRUNC, and allowing <sys/mman.h> to make visible all symbols from <fcntl.h>.

Austin Group Defect 850 is applied, adding MAP_ANON and MAP_ANONYMOUS.

End of informative text.

 

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