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MMAP(2)			    BSD Programmer's 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 len is not a multiple of the pagesize, the mapped
     region may extend past the specified range.  Any such extension beyond
     the end of the mapped object will be zero-filled.

     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
     range.

     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 op-
     tions 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 must be -1.
		 The offset parameter is ignored.

     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.

     MAP_PRIVATE
		 Modifications are private.

     MAP_SHARED	 Modifications are shared.

     The close(2) function does not unmap pages; see munmap(2) for further in-
     formation.

     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 de-
     vice to which swapping should be done.

RETURN VALUES
     Upon successful completion, mmap returns a pointer to the mapped region.
     Otherwise, a value of MAP_FAILED 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 param-
		   eter and fd was not open for reading.  The flags MAP_SHARED
		   and PROT_WRITE 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 addr parameter was not page
		   aligned or was outside of the valid address range for a
		   process.  MAP_ANON was specified and fd was not -1.	Fd did
		   not reference a regular or character special file.  Len was
		   less than zero.

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

SEE ALSO
     madvise(2),  mincore(2),  mprotect(2),  msync(2),	munmap(2),  getpage-
     size(3)

BUGS
     In previous releases of the system, the contents of a file as viewed with
     mmap() could appear different when viewed with read().  The system now
     automatically synchronizes memory backed by mmap() when a read() or
     write() call is performed on the corresponding region of the file.	 How-
     ever, it is still possible for memory backed by mmap() from an NFS file
     to be out of synchronization with the NFS server.	Such memory is guaran-
     teed to be no more out of date than the last read() or write() from the
     NFS client at the corresponding region of the file, so it is possible to
     force synchronization of a mapped file by using read() on the contents.

4th Berkeley Distribution	 March 4, 1998				     2
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