mmap man page on OpenDarwin

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MMAP(2)			    BSD System Calls Manual		       MMAP(2)

     mmap — map files or devices into memory

     #include <sys/types.h>
     #include <sys/mman.h>

     void *
     mmap(void *addr, size_t len, int prot, int flags, int fd, off_t offset);

     The mmap function causes the pages starting at addr and continuing for at
     most len bytes to be mapped from the object described by fd, starting at
     byte offset offset.  If offset or len is not a multiple of the pagesize,
     the mapped region may extend past the specified range.

     If addr is non-zero, it is used as a hint to the system.  (As a conve‐
     nience to the system, the actual address of the region may differ from
     the address supplied.)  If addr is zero, an address will be selected by
     the system.  The actual starting address of the region is returned.  A
     successful mmap deletes any previous mapping in the allocated address

     The protections (region accessibility) are specified in the prot argument
     by or'ing the following values:

     PROT_EXEC	 Pages may be executed.

     PROT_READ	 Pages may be read.

     PROT_WRITE	 Pages may be written.

     The flags parameter specifies the type of the mapped object, mapping
     options and whether modifications made to the mapped copy of the page are
     private to the process or are to be shared with other references.	Shar‐
     ing, mapping type and options are specified in the flags argument by
     or'ing the following values:

     MAP_ANON	 Map anonymous memory not associated with any specific file.
		 The file descriptor used for creating MAP_ANON regions is
		 used only for naming, and may be specified as -1 if no name
		 is associated with the region.

     MAP_FILE	 Mapped from a regular file or character-special device mem‐
		 ory.  (This is the default mapping type, and need not be

     MAP_FIXED	 Do not permit the system to select a different address than
		 the one specified.  If the specified address cannot be used,
		 mmap will fail.  If MAP_FIXED is specified, addr must be a
		 multiple of the pagesize.  Use of this option is discouraged.

		 Notify the kernel that the region may contain semaphores and
		 that special handling may be necessary.

		 Modifications are private.

     MAP_SHARED	 Modifications are shared.

     The close(2) function does not unmap pages, see munmap(2) for further

     The current design does not allow a process to specify the location of
     swap space.  In the future we may define an additional mapping type,
     MAP_SWAP, in which the file descriptor argument specifies a file or
     device to which swapping should be done.

     Upon successful completion, mmap returns a pointer to the mapped region.
     Otherwise, a value of -1 is returned and errno is set to indicate the

     Mmap() will fail if:

     [EACCES]		The flag PROT_READ was specified as part of the prot
			parameter and fd was not open for reading.  The flags
			PROT_WRITE and MAP_SHARED were specified as part of
			the flags and prot parameters and fd was not open for

     [EBADF]		fd is not a valid open file descriptor.

     [EINVAL]		MAP_FIXED was specified and the parameter was not page
			aligned.  fd did not reference a regular or character
			special file.

     [ENOMEM]		MAP_FIXED was specified and the addr parameter wasn't
			available.  MAP_ANON was specified and insufficient
			memory was available.

     getpagesize(2), msync(2), munmap(2), mprotect(2), madvise(2), mincore(2),

4th Berkeley Distribution	 June 4, 1993	     4th Berkeley Distribution

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