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OpenDarwin 7.2.1 - man page for mmap (opendarwin section 2)

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

NAME
     mmap -- map files or devices into memory

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

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

DESCRIPTION
     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 convenience 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 range.

     The protections (region accessibility) are specified in the prot argument by or'ing the fol-
     lowing 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.  Sharing, 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 memory.  (This is the
		 default mapping type, and need not be specified.)

     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 speci-
		 fied, addr must be a multiple of the pagesize.  Use of this option is discour-
		 aged.

     MAP_HASSEMAPHORE
		 Notify the kernel that the region may contain semaphores and that special han-
		 dling may be necessary.

     MAP_PRIVATE
		 Modifications are private.

     MAP_SHARED  Modifications are shared.

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

     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.

RETURN VALUES
     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 error.

ERRORS
     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 writing.

     [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.

SEE ALSO
     getpagesize(2), msync(2), munmap(2), mprotect(2), madvise(2), mincore(2), mlock(2)

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