MAP(2)                     BSD System Calls Manual                    MAP(2)

NAME
     mmap -- map files or devices into memory

SYNOPSIS
     ##include <>
     ##include <>

     void *
     mmap(void *addr, sizet len, int prot, int flags, int fd, offt 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:

     PROTEXEC   Pages may be executed.

     PROTREAD   Pages may be read.

     PROTWRITE  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:

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

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

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

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

     MAPRIVATE
                 Modifications are private.

     MAPSHARED  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,
     MAPSWAP, 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.

ERORS
     map() will fail if:

     [EACES]           The flag PROTREAD was specified as part of the prot
                        parameter and fd was not open for reading.  The flags
                        PROTWRITE and MAPSHARED 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]           MAPFIXED was specified and the parameter was not page
                        aligned.  fd did not reference a regular or character
                        special file.

     [ENOMEM]           MAPFIXED was specified and the addr parameter wasn't
                        available.  MAPANON 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