n                  Upon success, a nonnegative integer
                       representing the lowest numbered unused file
                       descriptor. The file descriptor points to the
                       shared memory object.
    -1                 Indicates failure. errno is set to indicate
                       the error:

                       o  EACCES - Permission to create the shared
                          memory object is denied, or the shared
                          memory object exists and the permissions
                          specified by oflag are denied, or O_TRUNC
                          is specified and write permission is
                          denied.

                       o  EEXIST - O_CREAT and O_EXCL are set, but
                          the named shared memory object already
                          exists.

                       o  EINTR - A signal has interrupted the shm_
                          open operation.

                       o  EINVAL - The shm_open operation is not
                          supported for the given name.

                       o  EMFILE - Too many file descriptors are
                          currently in use by this process.

                       o  ENAMETOOLONG - The length of the name
                          argument exceeds PATH_MAX or a pathname
                          component is longer than NAME_MAX.

                       o  ENFILE - Too many shared memory objects are
                          currently open in the system.

                       o  ENOENT - O_CREAT is not set and the named
                          shared memory object does not exist.

                       o  ENOSPC - Memory space for creation of the
                          new shared memory object is insufficient.