1 #include <linux/types.h>
2 #include <linux/major.h>
3 #include <linux/errno.h>
4 #include <linux/signal.h>
5 #include <linux/fcntl.h>
6 #include <linux/sched.h>
7 #include <linux/interrupt.h>
9 #include <linux/tty_driver.h>
10 #include <linux/tty_flip.h>
11 #include <linux/devpts_fs.h>
12 #include <linux/file.h>
13 #include <linux/console.h>
14 #include <linux/timer.h>
15 #include <linux/ctype.h>
18 #include <linux/string.h>
19 #include <linux/slab.h>
20 #include <linux/poll.h>
21 #include <linux/proc_fs.h>
22 #include <linux/init.h>
23 #include <linux/module.h>
24 #include <linux/device.h>
25 #include <linux/wait.h>
26 #include <linux/bitops.h>
27 #include <linux/delay.h>
28 #include <linux/seq_file.h>
30 #include <linux/uaccess.h>
31 #include <asm/system.h>
33 #include <linux/kbd_kern.h>
34 #include <linux/vt_kern.h>
35 #include <linux/selection.h>
37 #include <linux/kmod.h>
38 #include <linux/nsproxy.h>
41 * This guards the refcounted line discipline lists. The lock
42 * must be taken with irqs off because there are hangup path
43 * callers who will do ldisc lookups and cannot sleep.
46 static DEFINE_SPINLOCK(tty_ldisc_lock);
47 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
48 /* Line disc dispatch table */
49 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
52 * tty_register_ldisc - install a line discipline
54 * @new_ldisc: pointer to the ldisc object
56 * Installs a new line discipline into the kernel. The discipline
57 * is set up as unreferenced and then made available to the kernel
58 * from this point onwards.
61 * takes tty_ldisc_lock to guard against ldisc races
64 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
69 if (disc < N_TTY || disc >= NR_LDISCS)
72 spin_lock_irqsave(&tty_ldisc_lock, flags);
73 tty_ldiscs[disc] = new_ldisc;
74 new_ldisc->num = disc;
75 new_ldisc->refcount = 0;
76 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
80 EXPORT_SYMBOL(tty_register_ldisc);
83 * tty_unregister_ldisc - unload a line discipline
85 * @new_ldisc: pointer to the ldisc object
87 * Remove a line discipline from the kernel providing it is not
91 * takes tty_ldisc_lock to guard against ldisc races
94 int tty_unregister_ldisc(int disc)
99 if (disc < N_TTY || disc >= NR_LDISCS)
102 spin_lock_irqsave(&tty_ldisc_lock, flags);
103 if (tty_ldiscs[disc]->refcount)
106 tty_ldiscs[disc] = NULL;
107 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
111 EXPORT_SYMBOL(tty_unregister_ldisc);
115 * tty_ldisc_try_get - try and reference an ldisc
116 * @disc: ldisc number
118 * Attempt to open and lock a line discipline into place. Return
119 * the line discipline refcounted or an error.
122 static struct tty_ldisc *tty_ldisc_try_get(int disc)
125 struct tty_ldisc *ld;
126 struct tty_ldisc_ops *ldops;
129 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
131 return ERR_PTR(-ENOMEM);
133 spin_lock_irqsave(&tty_ldisc_lock, flags);
135 ldops = tty_ldiscs[disc];
136 /* Check the entry is defined */
138 /* If the module is being unloaded we can't use it */
139 if (!try_module_get(ldops->owner))
145 atomic_set(&ld->users, 0);
149 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
158 * tty_ldisc_get - take a reference to an ldisc
159 * @disc: ldisc number
161 * Takes a reference to a line discipline. Deals with refcounts and
162 * module locking counts. Returns NULL if the discipline is not available.
163 * Returns a pointer to the discipline and bumps the ref count if it is
167 * takes tty_ldisc_lock to guard against ldisc races
170 static struct tty_ldisc *tty_ldisc_get(int disc)
172 struct tty_ldisc *ld;
174 if (disc < N_TTY || disc >= NR_LDISCS)
175 return ERR_PTR(-EINVAL);
176 ld = tty_ldisc_try_get(disc);
178 request_module("tty-ldisc-%d", disc);
179 ld = tty_ldisc_try_get(disc);
185 * tty_ldisc_put - drop ldisc reference
188 * Drop a reference to a line discipline. Manage refcounts and
189 * module usage counts. Free the ldisc once the recount hits zero.
192 * takes tty_ldisc_lock to guard against ldisc races
195 static void tty_ldisc_put(struct tty_ldisc *ld)
198 int disc = ld->ops->num;
199 struct tty_ldisc_ops *ldo;
201 BUG_ON(disc < N_TTY || disc >= NR_LDISCS);
203 spin_lock_irqsave(&tty_ldisc_lock, flags);
204 ldo = tty_ldiscs[disc];
205 BUG_ON(ldo->refcount == 0);
207 module_put(ldo->owner);
208 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
209 WARN_ON(atomic_read(&ld->users));
213 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
215 return (*pos < NR_LDISCS) ? pos : NULL;
218 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
221 return (*pos < NR_LDISCS) ? pos : NULL;
224 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
228 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
230 int i = *(loff_t *)v;
231 struct tty_ldisc *ld;
233 ld = tty_ldisc_try_get(i);
236 seq_printf(m, "%-10s %2d\n", ld->ops->name ? ld->ops->name : "???", i);
241 static const struct seq_operations tty_ldiscs_seq_ops = {
242 .start = tty_ldiscs_seq_start,
243 .next = tty_ldiscs_seq_next,
244 .stop = tty_ldiscs_seq_stop,
245 .show = tty_ldiscs_seq_show,
248 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
250 return seq_open(file, &tty_ldiscs_seq_ops);
253 const struct file_operations tty_ldiscs_proc_fops = {
254 .owner = THIS_MODULE,
255 .open = proc_tty_ldiscs_open,
258 .release = seq_release,
262 * tty_ldisc_assign - set ldisc on a tty
263 * @tty: tty to assign
264 * @ld: line discipline
266 * Install an instance of a line discipline into a tty structure. The
267 * ldisc must have a reference count above zero to ensure it remains.
268 * The tty instance refcount starts at zero.
271 * Caller must hold references
274 static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
280 * tty_ldisc_try - internal helper
283 * Make a single attempt to grab and bump the refcount on
284 * the tty ldisc. Return 0 on failure or 1 on success. This is
285 * used to implement both the waiting and non waiting versions
288 * Locking: takes tty_ldisc_lock
291 static int tty_ldisc_try(struct tty_struct *tty)
294 struct tty_ldisc *ld;
297 spin_lock_irqsave(&tty_ldisc_lock, flags);
299 if (test_bit(TTY_LDISC, &tty->flags)) {
300 atomic_inc(&ld->users);
303 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
308 * tty_ldisc_ref_wait - wait for the tty ldisc
311 * Dereference the line discipline for the terminal and take a
312 * reference to it. If the line discipline is in flux then
313 * wait patiently until it changes.
315 * Note: Must not be called from an IRQ/timer context. The caller
316 * must also be careful not to hold other locks that will deadlock
317 * against a discipline change, such as an existing ldisc reference
318 * (which we check for)
320 * Locking: call functions take tty_ldisc_lock
323 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
325 /* wait_event is a macro */
326 wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
327 WARN_ON(atomic_read(&tty->ldisc->users) == 0);
330 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
333 * tty_ldisc_ref - get the tty ldisc
336 * Dereference the line discipline for the terminal and take a
337 * reference to it. If the line discipline is in flux then
338 * return NULL. Can be called from IRQ and timer functions.
340 * Locking: called functions take tty_ldisc_lock
343 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
345 if (tty_ldisc_try(tty))
349 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
352 * tty_ldisc_deref - free a tty ldisc reference
353 * @ld: reference to free up
355 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
356 * be called in IRQ context.
358 * Locking: takes tty_ldisc_lock
361 void tty_ldisc_deref(struct tty_ldisc *ld)
367 spin_lock_irqsave(&tty_ldisc_lock, flags);
368 if (atomic_read(&ld->users) == 0)
369 printk(KERN_ERR "tty_ldisc_deref: no references.\n");
370 else if (atomic_dec_and_test(&ld->users))
371 wake_up(&tty_ldisc_wait);
372 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
374 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
377 * tty_ldisc_enable - allow ldisc use
378 * @tty: terminal to activate ldisc on
380 * Set the TTY_LDISC flag when the line discipline can be called
381 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
382 * changing flag to indicate any ldisc change is now over.
384 * Note: nobody should set the TTY_LDISC bit except via this function.
385 * Clearing directly is allowed.
388 void tty_ldisc_enable(struct tty_struct *tty)
390 set_bit(TTY_LDISC, &tty->flags);
391 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
392 wake_up(&tty_ldisc_wait);
396 * tty_ldisc_flush - flush line discipline queue
399 * Flush the line discipline queue (if any) for this tty. If there
400 * is no line discipline active this is a no-op.
403 void tty_ldisc_flush(struct tty_struct *tty)
405 struct tty_ldisc *ld = tty_ldisc_ref(tty);
407 if (ld->ops->flush_buffer)
408 ld->ops->flush_buffer(tty);
411 tty_buffer_flush(tty);
413 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
416 * tty_set_termios_ldisc - set ldisc field
417 * @tty: tty structure
418 * @num: line discipline number
420 * This is probably overkill for real world processors but
421 * they are not on hot paths so a little discipline won't do
424 * Locking: takes termios_mutex
427 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
429 mutex_lock(&tty->termios_mutex);
430 tty->termios->c_line = num;
431 mutex_unlock(&tty->termios_mutex);
435 * tty_ldisc_open - open a line discipline
436 * @tty: tty we are opening the ldisc on
437 * @ld: discipline to open
439 * A helper opening method. Also a convenient debugging and check
443 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
445 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
447 return ld->ops->open(tty);
452 * tty_ldisc_close - close a line discipline
453 * @tty: tty we are opening the ldisc on
454 * @ld: discipline to close
456 * A helper close method. Also a convenient debugging and check
460 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
462 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
463 clear_bit(TTY_LDISC_OPEN, &tty->flags);
469 * tty_ldisc_restore - helper for tty ldisc change
470 * @tty: tty to recover
471 * @old: previous ldisc
473 * Restore the previous line discipline or N_TTY when a line discipline
474 * change fails due to an open error
477 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
480 struct tty_ldisc *new_ldisc;
483 /* There is an outstanding reference here so this is safe */
484 old = tty_ldisc_get(old->ops->num);
485 WARN_ON(IS_ERR(old));
486 tty_ldisc_assign(tty, old);
487 tty_set_termios_ldisc(tty, old->ops->num);
488 if (tty_ldisc_open(tty, old) < 0) {
490 /* This driver is always present */
491 new_ldisc = tty_ldisc_get(N_TTY);
492 if (IS_ERR(new_ldisc))
494 tty_ldisc_assign(tty, new_ldisc);
495 tty_set_termios_ldisc(tty, N_TTY);
496 r = tty_ldisc_open(tty, new_ldisc);
498 panic("Couldn't open N_TTY ldisc for "
500 tty_name(tty, buf), r);
505 * tty_ldisc_halt - shut down the line discipline
508 * Shut down the line discipline and work queue for this tty device.
509 * The TTY_LDISC flag being cleared ensures no further references can
510 * be obtained while the delayed work queue halt ensures that no more
511 * data is fed to the ldisc.
513 * In order to wait for any existing references to complete see
514 * tty_ldisc_wait_idle.
517 static int tty_ldisc_halt(struct tty_struct *tty)
519 clear_bit(TTY_LDISC, &tty->flags);
520 return cancel_delayed_work(&tty->buf.work);
524 * tty_ldisc_wait_idle - wait for the ldisc to become idle
525 * @tty: tty to wait for
527 * Wait for the line discipline to become idle. The discipline must
528 * have been halted for this to guarantee it remains idle.
530 * tty_ldisc_lock protects the ref counts currently.
533 static int tty_ldisc_wait_idle(struct tty_struct *tty)
536 spin_lock_irqsave(&tty_ldisc_lock, flags);
537 while (atomic_read(&tty->ldisc->users)) {
538 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
539 if (wait_event_timeout(tty_ldisc_wait,
540 atomic_read(&tty->ldisc->users) == 0, 5 * HZ) == 0)
542 spin_lock_irqsave(&tty_ldisc_lock, flags);
544 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
549 * tty_set_ldisc - set line discipline
550 * @tty: the terminal to set
551 * @ldisc: the line discipline
553 * Set the discipline of a tty line. Must be called from a process
554 * context. The ldisc change logic has to protect itself against any
555 * overlapping ldisc change (including on the other end of pty pairs),
556 * the close of one side of a tty/pty pair, and eventually hangup.
558 * Locking: takes tty_ldisc_lock, termios_mutex
561 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
564 struct tty_ldisc *o_ldisc, *new_ldisc;
565 int work, o_work = 0;
566 struct tty_struct *o_tty;
568 new_ldisc = tty_ldisc_get(ldisc);
569 if (IS_ERR(new_ldisc))
570 return PTR_ERR(new_ldisc);
573 * We need to look at the tty locking here for pty/tty pairs
574 * when both sides try to change in parallel.
577 o_tty = tty->link; /* o_tty is the pty side or NULL */
581 * Check the no-op case
584 if (tty->ldisc->ops->num == ldisc) {
585 tty_ldisc_put(new_ldisc);
590 * Problem: What do we do if this blocks ?
591 * We could deadlock here
594 tty_wait_until_sent(tty, 0);
596 mutex_lock(&tty->ldisc_mutex);
599 * We could be midstream of another ldisc change which has
600 * dropped the lock during processing. If so we need to wait.
603 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
604 mutex_unlock(&tty->ldisc_mutex);
605 wait_event(tty_ldisc_wait,
606 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
607 mutex_lock(&tty->ldisc_mutex);
609 set_bit(TTY_LDISC_CHANGING, &tty->flags);
612 * No more input please, we are switching. The new ldisc
613 * will update this value in the ldisc open function
616 tty->receive_room = 0;
618 o_ldisc = tty->ldisc;
620 * Make sure we don't change while someone holds a
621 * reference to the line discipline. The TTY_LDISC bit
622 * prevents anyone taking a reference once it is clear.
623 * We need the lock to avoid racing reference takers.
625 * We must clear the TTY_LDISC bit here to avoid a livelock
626 * with a userspace app continually trying to use the tty in
627 * parallel to the change and re-referencing the tty.
630 work = tty_ldisc_halt(tty);
632 o_work = tty_ldisc_halt(o_tty);
635 * Wait for ->hangup_work and ->buf.work handlers to terminate.
636 * We must drop the mutex here in case a hangup is also in process.
639 mutex_unlock(&tty->ldisc_mutex);
641 flush_scheduled_work();
643 /* Let any existing reference holders finish */
644 retval = tty_ldisc_wait_idle(tty);
646 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
647 tty_ldisc_put(new_ldisc);
651 mutex_lock(&tty->ldisc_mutex);
652 if (test_bit(TTY_HUPPED, &tty->flags)) {
653 /* We were raced by the hangup method. It will have stomped
654 the ldisc data and closed the ldisc down */
655 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
656 mutex_unlock(&tty->ldisc_mutex);
657 tty_ldisc_put(new_ldisc);
661 /* Shutdown the current discipline. */
662 tty_ldisc_close(tty, o_ldisc);
664 /* Now set up the new line discipline. */
665 tty_ldisc_assign(tty, new_ldisc);
666 tty_set_termios_ldisc(tty, ldisc);
668 retval = tty_ldisc_open(tty, new_ldisc);
670 /* Back to the old one or N_TTY if we can't */
671 tty_ldisc_put(new_ldisc);
672 tty_ldisc_restore(tty, o_ldisc);
675 /* At this point we hold a reference to the new ldisc and a
676 a reference to the old ldisc. If we ended up flipping back
677 to the existing ldisc we have two references to it */
679 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
680 tty->ops->set_ldisc(tty);
682 tty_ldisc_put(o_ldisc);
685 * Allow ldisc referencing to occur again
688 tty_ldisc_enable(tty);
690 tty_ldisc_enable(o_tty);
692 /* Restart the work queue in case no characters kick it off. Safe if
695 schedule_delayed_work(&tty->buf.work, 1);
697 schedule_delayed_work(&o_tty->buf.work, 1);
698 mutex_unlock(&tty->ldisc_mutex);
703 * tty_reset_termios - reset terminal state
706 * Restore a terminal to the driver default state.
709 static void tty_reset_termios(struct tty_struct *tty)
711 mutex_lock(&tty->termios_mutex);
712 *tty->termios = tty->driver->init_termios;
713 tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
714 tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
715 mutex_unlock(&tty->termios_mutex);
720 * tty_ldisc_reinit - reinitialise the tty ldisc
721 * @tty: tty to reinit
723 * Switch the tty back to N_TTY line discipline and leave the
727 static void tty_ldisc_reinit(struct tty_struct *tty)
729 struct tty_ldisc *ld;
731 tty_ldisc_close(tty, tty->ldisc);
732 tty_ldisc_put(tty->ldisc);
735 * Switch the line discipline back
737 ld = tty_ldisc_get(N_TTY);
739 tty_ldisc_assign(tty, ld);
740 tty_set_termios_ldisc(tty, N_TTY);
744 * tty_ldisc_hangup - hangup ldisc reset
745 * @tty: tty being hung up
747 * Some tty devices reset their termios when they receive a hangup
748 * event. In that situation we must also switch back to N_TTY properly
749 * before we reset the termios data.
751 * Locking: We can take the ldisc mutex as the rest of the code is
752 * careful to allow for this.
754 * In the pty pair case this occurs in the close() path of the
755 * tty itself so we must be careful about locking rules.
758 void tty_ldisc_hangup(struct tty_struct *tty)
760 struct tty_ldisc *ld;
763 * FIXME! What are the locking issues here? This may me overdoing
764 * things... This question is especially important now that we've
765 * removed the irqlock.
767 ld = tty_ldisc_ref(tty);
769 /* We may have no line discipline at this point */
770 if (ld->ops->flush_buffer)
771 ld->ops->flush_buffer(tty);
772 tty_driver_flush_buffer(tty);
773 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
774 ld->ops->write_wakeup)
775 ld->ops->write_wakeup(tty);
777 ld->ops->hangup(tty);
781 * FIXME: Once we trust the LDISC code better we can wait here for
782 * ldisc completion and fix the driver call race
784 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
785 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
787 * Shutdown the current line discipline, and reset it to
790 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
791 /* Avoid racing set_ldisc or tty_ldisc_release */
792 mutex_lock(&tty->ldisc_mutex);
793 if (tty->ldisc) { /* Not yet closed */
794 /* Switch back to N_TTY */
796 tty_ldisc_wait_idle(tty);
797 tty_ldisc_reinit(tty);
798 /* At this point we have a closed ldisc and we want to
799 reopen it. We could defer this to the next open but
800 it means auditing a lot of other paths so this is
802 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
803 tty_ldisc_enable(tty);
805 mutex_unlock(&tty->ldisc_mutex);
806 tty_reset_termios(tty);
811 * tty_ldisc_setup - open line discipline
812 * @tty: tty being shut down
813 * @o_tty: pair tty for pty/tty pairs
815 * Called during the initial open of a tty/pty pair in order to set up the
816 * line disciplines and bind them to the tty. This has no locking issues
817 * as the device isn't yet active.
820 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
822 struct tty_ldisc *ld = tty->ldisc;
825 retval = tty_ldisc_open(tty, ld);
830 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
832 tty_ldisc_close(tty, ld);
835 tty_ldisc_enable(o_tty);
837 tty_ldisc_enable(tty);
841 * tty_ldisc_release - release line discipline
842 * @tty: tty being shut down
843 * @o_tty: pair tty for pty/tty pairs
845 * Called during the final close of a tty/pty pair in order to shut down
846 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
847 * ldisc has not been opened.
850 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
853 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
854 * kill any delayed work. As this is the final close it does not
855 * race with the set_ldisc code path.
859 flush_scheduled_work();
862 * Wait for any short term users (we know they are just driver
863 * side waiters as the file is closing so user count on the file
867 tty_ldisc_wait_idle(tty);
869 mutex_lock(&tty->ldisc_mutex);
871 * Now kill off the ldisc
873 tty_ldisc_close(tty, tty->ldisc);
874 tty_ldisc_put(tty->ldisc);
875 /* Force an oops if we mess this up */
878 /* Ensure the next open requests the N_TTY ldisc */
879 tty_set_termios_ldisc(tty, N_TTY);
880 mutex_unlock(&tty->ldisc_mutex);
882 /* This will need doing differently if we need to lock */
884 tty_ldisc_release(o_tty, NULL);
886 /* And the memory resources remaining (buffers, termios) will be
887 disposed of when the kref hits zero */
891 * tty_ldisc_init - ldisc setup for new tty
892 * @tty: tty being allocated
894 * Set up the line discipline objects for a newly allocated tty. Note that
895 * the tty structure is not completely set up when this call is made.
898 void tty_ldisc_init(struct tty_struct *tty)
900 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
902 panic("n_tty: init_tty");
903 tty_ldisc_assign(tty, ld);
906 void tty_ldisc_begin(void)
908 /* Setup the default TTY line discipline. */
909 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);