x                  Upon successful completion, ttyname returns a
                       pointer to a null-terminated string.
    NULL               Upon failure, ttyname returns a NULL pointer
                       and sets errno to indicate the failure:

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

                       o  ENOTTY - The fildes argument does not refer
                          to a terminal device.

    0                  Upon successful completion, ttyname_r returns
                       0.
    n                  Upon failure, ttyname_r sets errno to indicate
                       the failure, and returns the same errno code:

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

                       o  ENOTTY - The fildes argument does not refer
                          to a TTY device.

                       o  ERANGE - The value of namesize is smaller
                          than the length of the string to be
                          returned including the terminating null
                          character.

    0                  For the legacy ttyname, indicates that
                       SYS$INPUT is not a TTY device.