mmap.2 (2010 09)

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mmap(2) mmap(2)

NAME

mmap() - map pages of memory

SYNOPSIS

#include <sys/mman.h>

void *mmap(void *addr, size_t len, int prot, int flags,

int fildes, off_t off);

DESCRIPTION

The mmap() function establishes a mapping between a process’ address space and a ﬁle. The format of

the call is as follows:

pa = mmap(addr, len, prot, flags, fildes, off);

The mmap() function establishes a mapping between the process’ address space at an address pa for len

bytes and the ﬁle associated with the ﬁle descriptor ﬁldes at offset off for len bytes. The value of pa is an

unspeciﬁed function of the argument addr and values of ﬂags, further described below. A successful

mmap() call returns pa as its result. The address ranges covered by [pa, pa +len] and [off, off+len] must

be legitimate for the possible (not necessarily current) address space of the process and the ﬁle, respec-

tively.

If the size of the mapped ﬁle changes after the call to

mmap(), the effect of references to portions of the

mapped region that correspond to added or removed portions of the ﬁle is unspeciﬁed.

The

mmap() function is supported for regular ﬁles. Support for any other type of ﬁle is unspeciﬁed

except for /dev/zero, which is supported in HP-UX. See also zero(7).

The prot argument determines whether read, write, execute, or some combination of accesses are permit-

ted to the pages being mapped. The protection options are deﬁned in

<sys/mman.h>:

PROT_READ Page can be read.

PROT_WRITE Page can be written.

PROT_EXEC Page can be executed.

PROT_NONE Page cannot be accessed.

The prot argument can be

PROT_NONE, or any combination of the bit-wise inclusive OR of the values of

PROT_READ, PROT_WRITE, and PROT_EXEC.IfPROT_NONE is not speciﬁed, the system may grant

other access permissions to the region in addition to those explicitly requested, except that write access

will not be granted unless PROT_WRITE is speciﬁed.

The following combinations of protection modes are supported:

PROT_NONE

PROT_READ

PROT_READ|PROT_EXECUTE

PROT_READ|PROT_WRITE

PROT_READ|PROT_WRITE|PROT_EXECUTE

The ﬂags argument provides other information about the handling of the mapped pages. The options are

deﬁned in <sys/mman.h>:

MAP_SHARED Share changes.

MAP_ADDR32 Share changes between 32-bit and 64-bit processes. Under Adaptive

Address Space, 64-bit MPAS (Mostly Private Address Space)

processes cannot specify this ﬂag. See the Adaptive Address Space

Whitepaper for details.

MAP_PRIVATE Changes are private.

MAP_FIXED Interpret addr exactly.

MAP_FILE Create a mapped ﬁle region.

MAP_ANONYMOUS Create an unnamed memory region.

MAP_VARIABLE Place region at implementation-computed address.

MAP_NORESERVE Evaluate lazy swap space reservation.

MAP_GLOBAL Allocate physical memory from the global quadrant / octant.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (8 pages)

PAGE 1
mmap(2) mmap(2) NAME mmap() - map pages of memory SYNOPSIS #include void *mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t off); DESCRIPTION The mmap() function establishes a mapping between a process’ address space and a file.
PAGE 2
mmap(2) mmap(2) MAP_IO Create a virtual mapping for a physical I/O address range. MAP_MEM_INTERLEAVED Physical memory will be interleaved. MAP_MEM_LOCAL Allocate physical memory from the current locality domain. MAP_MEM_FIRST_TOUCH Allocate physical memory from the locality domain of the first processor to touch each address. The MAP_PRIVATE and MAP_SHARED flags control the visibility of write references to the memory region. Exactly one of these flags must be specified.
PAGE 3
mmap(2) mmap(2) The MAP_FILE and MAP_ANONYMOUS flags control whether the region to be mapped is a mapped file region or an anonymous shared memory region. Exactly one of these flags must be selected. If MAP_FILE is set in flags, a new mapped file region is created, mapping the file associated with fildes . off specifies the file byte offset at which the mapping starts. This offset must be a multiple of the page size returned by sysconf(_SC_PAGE_SIZE).
PAGE 4
mmap(2) mmap(2) the mpctl (2) manual page. These flags are hints to the system. If memory of the desired type is not available, the next most suitable memory is returned instead. mmap() cannot create a mapped file region unless the file descriptor used to map the file is open for reading. For a mapped file region that is mapped with MAP_SHARED, mmap() grants write access permission only if the file descriptor is open for writing.
PAGE 5
mmap(2) mmap(2) support fine-grained privileges. RETURN VALUE Upon successful completion, mmap() returns the address, (pa ), at which the mapping was placed. Otherwise, it returns MAP_FAILED (defined in ) and sets errno to indicate the error. ERRORS The mmap() function will fail if: [EBADF] The fildes argument is not a valid open file descriptor.
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mmap(2) mmap(2) shared between processes. This implies the following: • Any single range of a file cannot be mapped multiple times into different virtual address ranges.
PAGE 7
mmap(2) mmap(2) becomes: fildes = open(...) address = mmap(0, len, PROT_READ, MAP_PRIVATE, fildes, some_offset) /* use data at address */ AUTHOR mmap() was developed by HP, AT&T, and OSF. SEE ALSO setmemwindow(1M), creat64(2), exec(2), fcntl(2), fork(2), lockf(2), madvise(2), mpctl(2), mprotect(2), msem_init(2), msem_lock(2), msem_unlock(2), msync(2), munmap(2), open(2), pset_ctl(2), shmop(2), sysconf(2), truncate(2), mman(5), privileges(5), stat(5), zero(7).
PAGE 8
(Notes) A (Notes) mA 8 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010