addr

    The starting address of the new region (must be the page
    boundary).

 len

    The length, in bytes, of the new region.

 prot

    Access permission, as defined in the <mman.h> header file.
    Specify either PROT_NONE, PROT_READ, or PROT_WRITE.

 flags

    Attributes of the mapped region as the results of a bitwise-
    inclusive OR operation on any combination of the following:

    o  MAP_FILE or MAP_ANONYMOUS

    o  MAP_VARIABLE or MAP_FIXED

    o  MAP_SHARED or MAP_PRIVATE

 filedes

    The file that you want to map to the new mapped file region
    returned by the open function.

 off

    The offset, specified in bytes. The off_t data type is either a
    64-bit or 32-bit integer. The 64-bit interface allows for file
    sizes greater than 2 GB, and can be selected at compile time by
    defining the _LARGEFILE feature-test macro as follows:

    CC/DEFINE=_LARGEFILE

  . . .

    An optional integer specifying additional flags for the
    SYS$CRMPSC system service for MAP_SHARED. This optional argument
    (VSI C Extension) of the mmap function was introduced in
    OpenVMS Version 7.2.