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

NAME
     mmap -- map files or devices into memory

SYNOPSIS
     #include <&lt;sys/types.h>&gt;
     #include <&lt;sys/mman.h>&gt;

     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 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
     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
                 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 specified, addr must be a
                 multiple of the pagesize.  Use of this option is discouraged.

     MAP_HASSEMAPHORE
                 Notify the kernel that the region may contain semaphores and
                 that special handling 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