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/smp_lock.h> /* For the moment */
39 #include <linux/kmod.h>
40 #include <linux/nsproxy.h>
43 * This guards the refcounted line discipline lists. The lock
44 * must be taken with irqs off because there are hangup path
45 * callers who will do ldisc lookups and cannot sleep.
48 static DEFINE_SPINLOCK(tty_ldisc_lock);
49 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
50 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
51 /* Line disc dispatch table */
52 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
54 static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
57 atomic_inc(&ld->users);
61 static void put_ldisc(struct tty_ldisc *ld)
65 if (WARN_ON_ONCE(!ld))
69 * If this is the last user, free the ldisc, and
70 * release the ldisc ops.
72 * We really want an "atomic_dec_and_lock_irqsave()",
73 * but we don't have it, so this does it by hand.
75 local_irq_save(flags);
76 if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
77 struct tty_ldisc_ops *ldo = ld->ops;
80 module_put(ldo->owner);
81 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
86 local_irq_restore(flags);
87 wake_up(&tty_ldisc_idle);
91 * tty_register_ldisc - install a line discipline
93 * @new_ldisc: pointer to the ldisc object
95 * Installs a new line discipline into the kernel. The discipline
96 * is set up as unreferenced and then made available to the kernel
97 * from this point onwards.
100 * takes tty_ldisc_lock to guard against ldisc races
103 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
108 if (disc < N_TTY || disc >= NR_LDISCS)
111 spin_lock_irqsave(&tty_ldisc_lock, flags);
112 tty_ldiscs[disc] = new_ldisc;
113 new_ldisc->num = disc;
114 new_ldisc->refcount = 0;
115 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
119 EXPORT_SYMBOL(tty_register_ldisc);
122 * tty_unregister_ldisc - unload a line discipline
123 * @disc: ldisc number
124 * @new_ldisc: pointer to the ldisc object
126 * Remove a line discipline from the kernel providing it is not
130 * takes tty_ldisc_lock to guard against ldisc races
133 int tty_unregister_ldisc(int disc)
138 if (disc < N_TTY || disc >= NR_LDISCS)
141 spin_lock_irqsave(&tty_ldisc_lock, flags);
142 if (tty_ldiscs[disc]->refcount)
145 tty_ldiscs[disc] = NULL;
146 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
150 EXPORT_SYMBOL(tty_unregister_ldisc);
152 static struct tty_ldisc_ops *get_ldops(int disc)
155 struct tty_ldisc_ops *ldops, *ret;
157 spin_lock_irqsave(&tty_ldisc_lock, flags);
158 ret = ERR_PTR(-EINVAL);
159 ldops = tty_ldiscs[disc];
161 ret = ERR_PTR(-EAGAIN);
162 if (try_module_get(ldops->owner)) {
167 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
171 static void put_ldops(struct tty_ldisc_ops *ldops)
175 spin_lock_irqsave(&tty_ldisc_lock, flags);
177 module_put(ldops->owner);
178 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
182 * tty_ldisc_get - take a reference to an ldisc
183 * @disc: ldisc number
185 * Takes a reference to a line discipline. Deals with refcounts and
186 * module locking counts. Returns NULL if the discipline is not available.
187 * Returns a pointer to the discipline and bumps the ref count if it is
191 * takes tty_ldisc_lock to guard against ldisc races
194 static struct tty_ldisc *tty_ldisc_get(int disc)
196 struct tty_ldisc *ld;
197 struct tty_ldisc_ops *ldops;
199 if (disc < N_TTY || disc >= NR_LDISCS)
200 return ERR_PTR(-EINVAL);
203 * Get the ldisc ops - we may need to request them to be loaded
204 * dynamically and try again.
206 ldops = get_ldops(disc);
208 request_module("tty-ldisc-%d", disc);
209 ldops = get_ldops(disc);
211 return ERR_CAST(ldops);
214 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
217 return ERR_PTR(-ENOMEM);
221 atomic_set(&ld->users, 1);
225 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
227 return (*pos < NR_LDISCS) ? pos : NULL;
230 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
233 return (*pos < NR_LDISCS) ? pos : NULL;
236 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
240 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
242 int i = *(loff_t *)v;
243 struct tty_ldisc_ops *ldops;
245 ldops = get_ldops(i);
248 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
253 static const struct seq_operations tty_ldiscs_seq_ops = {
254 .start = tty_ldiscs_seq_start,
255 .next = tty_ldiscs_seq_next,
256 .stop = tty_ldiscs_seq_stop,
257 .show = tty_ldiscs_seq_show,
260 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
262 return seq_open(file, &tty_ldiscs_seq_ops);
265 const struct file_operations tty_ldiscs_proc_fops = {
266 .owner = THIS_MODULE,
267 .open = proc_tty_ldiscs_open,
270 .release = seq_release,
274 * tty_ldisc_assign - set ldisc on a tty
275 * @tty: tty to assign
276 * @ld: line discipline
278 * Install an instance of a line discipline into a tty structure. The
279 * ldisc must have a reference count above zero to ensure it remains.
280 * The tty instance refcount starts at zero.
283 * Caller must hold references
286 static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
292 * tty_ldisc_try - internal helper
295 * Make a single attempt to grab and bump the refcount on
296 * the tty ldisc. Return 0 on failure or 1 on success. This is
297 * used to implement both the waiting and non waiting versions
300 * Locking: takes tty_ldisc_lock
303 static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
306 struct tty_ldisc *ld;
308 spin_lock_irqsave(&tty_ldisc_lock, flags);
310 if (test_bit(TTY_LDISC, &tty->flags))
311 ld = get_ldisc(tty->ldisc);
312 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
317 * tty_ldisc_ref_wait - wait for the tty ldisc
320 * Dereference the line discipline for the terminal and take a
321 * reference to it. If the line discipline is in flux then
322 * wait patiently until it changes.
324 * Note: Must not be called from an IRQ/timer context. The caller
325 * must also be careful not to hold other locks that will deadlock
326 * against a discipline change, such as an existing ldisc reference
327 * (which we check for)
329 * Locking: call functions take tty_ldisc_lock
332 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
334 struct tty_ldisc *ld;
336 /* wait_event is a macro */
337 wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
340 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
343 * tty_ldisc_ref - get the tty ldisc
346 * Dereference the line discipline for the terminal and take a
347 * reference to it. If the line discipline is in flux then
348 * return NULL. Can be called from IRQ and timer functions.
350 * Locking: called functions take tty_ldisc_lock
353 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
355 return tty_ldisc_try(tty);
357 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
360 * tty_ldisc_deref - free a tty ldisc reference
361 * @ld: reference to free up
363 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
364 * be called in IRQ context.
366 * Locking: takes tty_ldisc_lock
369 void tty_ldisc_deref(struct tty_ldisc *ld)
373 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
375 static inline void tty_ldisc_put(struct tty_ldisc *ld)
381 * tty_ldisc_enable - allow ldisc use
382 * @tty: terminal to activate ldisc on
384 * Set the TTY_LDISC flag when the line discipline can be called
385 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
386 * changing flag to indicate any ldisc change is now over.
388 * Note: nobody should set the TTY_LDISC bit except via this function.
389 * Clearing directly is allowed.
392 void tty_ldisc_enable(struct tty_struct *tty)
394 set_bit(TTY_LDISC, &tty->flags);
395 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
396 wake_up(&tty_ldisc_wait);
400 * tty_ldisc_flush - flush line discipline queue
403 * Flush the line discipline queue (if any) for this tty. If there
404 * is no line discipline active this is a no-op.
407 void tty_ldisc_flush(struct tty_struct *tty)
409 struct tty_ldisc *ld = tty_ldisc_ref(tty);
411 if (ld->ops->flush_buffer)
412 ld->ops->flush_buffer(tty);
415 tty_buffer_flush(tty);
417 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
420 * tty_set_termios_ldisc - set ldisc field
421 * @tty: tty structure
422 * @num: line discipline number
424 * This is probably overkill for real world processors but
425 * they are not on hot paths so a little discipline won't do
428 * Locking: takes termios_mutex
431 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
433 mutex_lock(&tty->termios_mutex);
434 tty->termios->c_line = num;
435 mutex_unlock(&tty->termios_mutex);
439 * tty_ldisc_open - open a line discipline
440 * @tty: tty we are opening the ldisc on
441 * @ld: discipline to open
443 * A helper opening method. Also a convenient debugging and check
446 * Locking: always called with BTM already held.
449 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
451 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
454 /* BTM here locks versus a hangup event */
455 WARN_ON(!tty_locked());
456 ret = ld->ops->open(tty);
463 * tty_ldisc_close - close a line discipline
464 * @tty: tty we are opening the ldisc on
465 * @ld: discipline to close
467 * A helper close method. Also a convenient debugging and check
471 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
473 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
474 clear_bit(TTY_LDISC_OPEN, &tty->flags);
480 * tty_ldisc_restore - helper for tty ldisc change
481 * @tty: tty to recover
482 * @old: previous ldisc
484 * Restore the previous line discipline or N_TTY when a line discipline
485 * change fails due to an open error
488 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
491 struct tty_ldisc *new_ldisc;
494 /* There is an outstanding reference here so this is safe */
495 old = tty_ldisc_get(old->ops->num);
496 WARN_ON(IS_ERR(old));
497 tty_ldisc_assign(tty, old);
498 tty_set_termios_ldisc(tty, old->ops->num);
499 if (tty_ldisc_open(tty, old) < 0) {
501 /* This driver is always present */
502 new_ldisc = tty_ldisc_get(N_TTY);
503 if (IS_ERR(new_ldisc))
505 tty_ldisc_assign(tty, new_ldisc);
506 tty_set_termios_ldisc(tty, N_TTY);
507 r = tty_ldisc_open(tty, new_ldisc);
509 panic("Couldn't open N_TTY ldisc for "
511 tty_name(tty, buf), r);
516 * tty_ldisc_halt - shut down the line discipline
519 * Shut down the line discipline and work queue for this tty device.
520 * The TTY_LDISC flag being cleared ensures no further references can
521 * be obtained while the delayed work queue halt ensures that no more
522 * data is fed to the ldisc.
524 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
525 * in order to make sure any currently executing ldisc work is also
529 static int tty_ldisc_halt(struct tty_struct *tty)
531 clear_bit(TTY_LDISC, &tty->flags);
532 return cancel_delayed_work_sync(&tty->buf.work);
536 * tty_ldisc_wait_idle - wait for the ldisc to become idle
537 * @tty: tty to wait for
539 * Wait for the line discipline to become idle. The discipline must
540 * have been halted for this to guarantee it remains idle.
542 static int tty_ldisc_wait_idle(struct tty_struct *tty)
545 ret = wait_event_interruptible_timeout(tty_ldisc_idle,
546 atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
549 return ret > 0 ? 0 : -EBUSY;
553 * tty_set_ldisc - set line discipline
554 * @tty: the terminal to set
555 * @ldisc: the line discipline
557 * Set the discipline of a tty line. Must be called from a process
558 * context. The ldisc change logic has to protect itself against any
559 * overlapping ldisc change (including on the other end of pty pairs),
560 * the close of one side of a tty/pty pair, and eventually hangup.
562 * Locking: takes tty_ldisc_lock, termios_mutex
565 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
568 struct tty_ldisc *o_ldisc, *new_ldisc;
569 int work, o_work = 0;
570 struct tty_struct *o_tty;
572 new_ldisc = tty_ldisc_get(ldisc);
573 if (IS_ERR(new_ldisc))
574 return PTR_ERR(new_ldisc);
578 * We need to look at the tty locking here for pty/tty pairs
579 * when both sides try to change in parallel.
582 o_tty = tty->link; /* o_tty is the pty side or NULL */
586 * Check the no-op case
589 if (tty->ldisc->ops->num == ldisc) {
591 tty_ldisc_put(new_ldisc);
597 * Problem: What do we do if this blocks ?
598 * We could deadlock here
601 tty_wait_until_sent(tty, 0);
604 mutex_lock(&tty->ldisc_mutex);
607 * We could be midstream of another ldisc change which has
608 * dropped the lock during processing. If so we need to wait.
611 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
612 mutex_unlock(&tty->ldisc_mutex);
614 wait_event(tty_ldisc_wait,
615 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
617 mutex_lock(&tty->ldisc_mutex);
620 set_bit(TTY_LDISC_CHANGING, &tty->flags);
623 * No more input please, we are switching. The new ldisc
624 * will update this value in the ldisc open function
627 tty->receive_room = 0;
629 o_ldisc = tty->ldisc;
633 * Make sure we don't change while someone holds a
634 * reference to the line discipline. The TTY_LDISC bit
635 * prevents anyone taking a reference once it is clear.
636 * We need the lock to avoid racing reference takers.
638 * We must clear the TTY_LDISC bit here to avoid a livelock
639 * with a userspace app continually trying to use the tty in
640 * parallel to the change and re-referencing the tty.
643 work = tty_ldisc_halt(tty);
645 o_work = tty_ldisc_halt(o_tty);
648 * Wait for ->hangup_work and ->buf.work handlers to terminate.
649 * We must drop the mutex here in case a hangup is also in process.
652 mutex_unlock(&tty->ldisc_mutex);
654 flush_scheduled_work();
656 retval = tty_ldisc_wait_idle(tty);
659 mutex_lock(&tty->ldisc_mutex);
661 /* handle wait idle failure locked */
663 tty_ldisc_put(new_ldisc);
667 if (test_bit(TTY_HUPPED, &tty->flags)) {
668 /* We were raced by the hangup method. It will have stomped
669 the ldisc data and closed the ldisc down */
670 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
671 mutex_unlock(&tty->ldisc_mutex);
672 tty_ldisc_put(new_ldisc);
677 /* Shutdown the current discipline. */
678 tty_ldisc_close(tty, o_ldisc);
680 /* Now set up the new line discipline. */
681 tty_ldisc_assign(tty, new_ldisc);
682 tty_set_termios_ldisc(tty, ldisc);
684 retval = tty_ldisc_open(tty, new_ldisc);
686 /* Back to the old one or N_TTY if we can't */
687 tty_ldisc_put(new_ldisc);
688 tty_ldisc_restore(tty, o_ldisc);
691 /* At this point we hold a reference to the new ldisc and a
692 a reference to the old ldisc. If we ended up flipping back
693 to the existing ldisc we have two references to it */
695 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
696 tty->ops->set_ldisc(tty);
698 tty_ldisc_put(o_ldisc);
702 * Allow ldisc referencing to occur again
705 tty_ldisc_enable(tty);
707 tty_ldisc_enable(o_tty);
709 /* Restart the work queue in case no characters kick it off. Safe if
712 schedule_delayed_work(&tty->buf.work, 1);
714 schedule_delayed_work(&o_tty->buf.work, 1);
715 mutex_unlock(&tty->ldisc_mutex);
721 * tty_reset_termios - reset terminal state
724 * Restore a terminal to the driver default state.
727 static void tty_reset_termios(struct tty_struct *tty)
729 mutex_lock(&tty->termios_mutex);
730 *tty->termios = tty->driver->init_termios;
731 tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
732 tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
733 mutex_unlock(&tty->termios_mutex);
738 * tty_ldisc_reinit - reinitialise the tty ldisc
739 * @tty: tty to reinit
740 * @ldisc: line discipline to reinitialize
742 * Switch the tty to a line discipline and leave the ldisc
746 static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
748 struct tty_ldisc *ld = tty_ldisc_get(ldisc);
753 tty_ldisc_close(tty, tty->ldisc);
754 tty_ldisc_put(tty->ldisc);
757 * Switch the line discipline back
759 tty_ldisc_assign(tty, ld);
760 tty_set_termios_ldisc(tty, ldisc);
766 * tty_ldisc_hangup - hangup ldisc reset
767 * @tty: tty being hung up
769 * Some tty devices reset their termios when they receive a hangup
770 * event. In that situation we must also switch back to N_TTY properly
771 * before we reset the termios data.
773 * Locking: We can take the ldisc mutex as the rest of the code is
774 * careful to allow for this.
776 * In the pty pair case this occurs in the close() path of the
777 * tty itself so we must be careful about locking rules.
780 void tty_ldisc_hangup(struct tty_struct *tty)
782 struct tty_ldisc *ld;
783 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
787 * FIXME! What are the locking issues here? This may me overdoing
788 * things... This question is especially important now that we've
789 * removed the irqlock.
791 ld = tty_ldisc_ref(tty);
793 /* We may have no line discipline at this point */
794 if (ld->ops->flush_buffer)
795 ld->ops->flush_buffer(tty);
796 tty_driver_flush_buffer(tty);
797 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
798 ld->ops->write_wakeup)
799 ld->ops->write_wakeup(tty);
801 ld->ops->hangup(tty);
805 * FIXME: Once we trust the LDISC code better we can wait here for
806 * ldisc completion and fix the driver call race
808 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
809 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
811 * Shutdown the current line discipline, and reset it to
814 * Avoid racing set_ldisc or tty_ldisc_release
816 mutex_lock(&tty->ldisc_mutex);
819 * this is like tty_ldisc_halt, but we need to give up
820 * the BTM before calling cancel_delayed_work_sync,
821 * which may need to wait for another function taking the BTM
823 clear_bit(TTY_LDISC, &tty->flags);
825 cancel_delayed_work_sync(&tty->buf.work);
826 mutex_unlock(&tty->ldisc_mutex);
829 mutex_lock(&tty->ldisc_mutex);
831 /* At this point we have a closed ldisc and we want to
832 reopen it. We could defer this to the next open but
833 it means auditing a lot of other paths so this is
835 if (tty->ldisc) { /* Not yet closed */
838 if (!tty_ldisc_reinit(tty, tty->termios->c_line))
839 err = tty_ldisc_open(tty, tty->ldisc);
843 /* If the re-open fails or we reset then go to N_TTY. The
844 N_TTY open cannot fail */
846 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
847 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
849 tty_ldisc_enable(tty);
851 mutex_unlock(&tty->ldisc_mutex);
853 tty_reset_termios(tty);
857 * tty_ldisc_setup - open line discipline
858 * @tty: tty being shut down
859 * @o_tty: pair tty for pty/tty pairs
861 * Called during the initial open of a tty/pty pair in order to set up the
862 * line disciplines and bind them to the tty. This has no locking issues
863 * as the device isn't yet active.
866 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
868 struct tty_ldisc *ld = tty->ldisc;
871 retval = tty_ldisc_open(tty, ld);
876 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
878 tty_ldisc_close(tty, ld);
881 tty_ldisc_enable(o_tty);
883 tty_ldisc_enable(tty);
887 * tty_ldisc_release - release line discipline
888 * @tty: tty being shut down
889 * @o_tty: pair tty for pty/tty pairs
891 * Called during the final close of a tty/pty pair in order to shut down
892 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
893 * ldisc has not been opened.
896 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
899 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
900 * kill any delayed work. As this is the final close it does not
901 * race with the set_ldisc code path.
906 flush_scheduled_work();
909 mutex_lock(&tty->ldisc_mutex);
911 * Now kill off the ldisc
913 tty_ldisc_close(tty, tty->ldisc);
914 tty_ldisc_put(tty->ldisc);
915 /* Force an oops if we mess this up */
918 /* Ensure the next open requests the N_TTY ldisc */
919 tty_set_termios_ldisc(tty, N_TTY);
920 mutex_unlock(&tty->ldisc_mutex);
922 /* This will need doing differently if we need to lock */
924 tty_ldisc_release(o_tty, NULL);
926 /* And the memory resources remaining (buffers, termios) will be
927 disposed of when the kref hits zero */
931 * tty_ldisc_init - ldisc setup for new tty
932 * @tty: tty being allocated
934 * Set up the line discipline objects for a newly allocated tty. Note that
935 * the tty structure is not completely set up when this call is made.
938 void tty_ldisc_init(struct tty_struct *tty)
940 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
942 panic("n_tty: init_tty");
943 tty_ldisc_assign(tty, ld);
946 void tty_ldisc_begin(void)
948 /* Setup the default TTY line discipline. */
949 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);