+/**
+ * tty_ldisc_restore - helper for tty ldisc change
+ * @tty: tty to recover
+ * @old: previous ldisc
+ *
+ * Restore the previous line discipline or N_TTY when a line discipline
+ * change fails due to an open error
+ */
+
+static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
+{
+ struct tty_ldisc *new_ldisc;
+ int r;
+
+ /* There is an outstanding reference here so this is safe */
+ old = tty_ldisc_get(tty, old->ops->num);
+ WARN_ON(IS_ERR(old));
+ tty->ldisc = old;
+ tty_set_termios_ldisc(tty, old->ops->num);
+ if (tty_ldisc_open(tty, old) < 0) {
+ tty_ldisc_put(old);
+ /* This driver is always present */
+ new_ldisc = tty_ldisc_get(tty, N_TTY);
+ if (IS_ERR(new_ldisc))
+ panic("n_tty: get");
+ tty->ldisc = new_ldisc;
+ tty_set_termios_ldisc(tty, N_TTY);
+ r = tty_ldisc_open(tty, new_ldisc);
+ if (r < 0)
+ panic("Couldn't open N_TTY ldisc for "
+ "%s --- error %d.",
+ tty_name(tty), r);
+ }
+}
+