x                  The address where the mapping is placed.
    MAP_FAILED         Indicates an error; errno is set to one of the
                       following values:

                       o  EACCES - The file referred to by filedes
                          is not open for read access, or the file
                          is not open for write access and PROT_WRITE
                          was set for a MAP_SHARED mapping operation.

                       o  EBADF - The filedes argument is not a valid
                          file descriptor.

                       o  EINVAL -The flags or prot argument is
                          invalid, or the addr argument or off
                          argument is not a multiple of the page
                          size returned by sysconf(_SC_PAGE_SIZE).

                       o  ENODEV - The file descriptor filedes refers
                          to an object that cannot be mapped, such as
                          a terminal.

                       o  ENOMEM - There is not enough address space
                          to map len bytes.

                       o  ENXIO - The addresses specified by the
                          range [off, off + len] are invalid for
                          filedes.

                       o  EFAULT - The addr argument is an invalid
                          address.