pty: return EINVAL for TIOCGPTN for BSD ptys

Commit bbb63c514a3464342967237a51a21ea8f61ab951 (drivers:tty:fix up
ENOIOCTLCMD error handling) changed the default return value from tty
ioctl to be ENOTTY and not EINVAL. This is appropriate.

But in case of TIOCGPTN for the old BSD ptys glibc started failing
because it expects EINVAL to be returned. Only then it continues to
obtain the pts name the other way around.

So fix this case by explicit return of EINVAL in this case.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: Florian Westphal <fw@strlen.de>
Cc: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@vger.kernel.org> # 3.7+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -441,6 +441,8 @@ static int pty_bsd_ioctl(struct tty_struct *tty,
 		return pty_get_pktmode(tty, (int __user *)arg);
 	case TIOCSIG:    /* Send signal to other side of pty */
 		return pty_signal(tty, (int) arg);
+	case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
+		return -EINVAL;
 	}
 	return -ENOIOCTLCMD;
 }