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>
39 #include <linux/ratelimit.h>
42 * This guards the refcounted line discipline lists. The lock
43 * must be taken with irqs off because there are hangup path
44 * callers who will do ldisc lookups and cannot sleep.
47 static DEFINE_SPINLOCK(tty_ldisc_lock);
48 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
49 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
50 /* Line disc dispatch table */
51 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
53 static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
56 atomic_inc(&ld->users);
60 static void put_ldisc(struct tty_ldisc *ld)
64 if (WARN_ON_ONCE(!ld))
68 * If this is the last user, free the ldisc, and
69 * release the ldisc ops.
71 * We really want an "atomic_dec_and_lock_irqsave()",
72 * but we don't have it, so this does it by hand.
74 local_irq_save(flags);
75 if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
76 struct tty_ldisc_ops *ldo = ld->ops;
79 module_put(ldo->owner);
80 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
85 local_irq_restore(flags);
86 wake_up(&tty_ldisc_idle);
90 * tty_register_ldisc - install a line discipline
92 * @new_ldisc: pointer to the ldisc object
94 * Installs a new line discipline into the kernel. The discipline
95 * is set up as unreferenced and then made available to the kernel
96 * from this point onwards.
99 * takes tty_ldisc_lock to guard against ldisc races
102 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
107 if (disc < N_TTY || disc >= NR_LDISCS)
110 spin_lock_irqsave(&tty_ldisc_lock, flags);
111 tty_ldiscs[disc] = new_ldisc;
112 new_ldisc->num = disc;
113 new_ldisc->refcount = 0;
114 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
118 EXPORT_SYMBOL(tty_register_ldisc);
121 * tty_unregister_ldisc - unload a line discipline
122 * @disc: ldisc number
123 * @new_ldisc: pointer to the ldisc object
125 * Remove a line discipline from the kernel providing it is not
129 * takes tty_ldisc_lock to guard against ldisc races
132 int tty_unregister_ldisc(int disc)
137 if (disc < N_TTY || disc >= NR_LDISCS)
140 spin_lock_irqsave(&tty_ldisc_lock, flags);
141 if (tty_ldiscs[disc]->refcount)
144 tty_ldiscs[disc] = NULL;
145 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
149 EXPORT_SYMBOL(tty_unregister_ldisc);
151 static struct tty_ldisc_ops *get_ldops(int disc)
154 struct tty_ldisc_ops *ldops, *ret;
156 spin_lock_irqsave(&tty_ldisc_lock, flags);
157 ret = ERR_PTR(-EINVAL);
158 ldops = tty_ldiscs[disc];
160 ret = ERR_PTR(-EAGAIN);
161 if (try_module_get(ldops->owner)) {
166 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
170 static void put_ldops(struct tty_ldisc_ops *ldops)
174 spin_lock_irqsave(&tty_ldisc_lock, flags);
176 module_put(ldops->owner);
177 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
181 * tty_ldisc_get - take a reference to an ldisc
182 * @disc: ldisc number
184 * Takes a reference to a line discipline. Deals with refcounts and
185 * module locking counts. Returns NULL if the discipline is not available.
186 * Returns a pointer to the discipline and bumps the ref count if it is
190 * takes tty_ldisc_lock to guard against ldisc races
193 static struct tty_ldisc *tty_ldisc_get(int disc)
195 struct tty_ldisc *ld;
196 struct tty_ldisc_ops *ldops;
198 if (disc < N_TTY || disc >= NR_LDISCS)
199 return ERR_PTR(-EINVAL);
202 * Get the ldisc ops - we may need to request them to be loaded
203 * dynamically and try again.
205 ldops = get_ldops(disc);
207 request_module("tty-ldisc-%d", disc);
208 ldops = get_ldops(disc);
210 return ERR_CAST(ldops);
213 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
216 return ERR_PTR(-ENOMEM);
220 atomic_set(&ld->users, 1);
224 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
226 return (*pos < NR_LDISCS) ? pos : NULL;
229 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
232 return (*pos < NR_LDISCS) ? pos : NULL;
235 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
239 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
241 int i = *(loff_t *)v;
242 struct tty_ldisc_ops *ldops;
244 ldops = get_ldops(i);
247 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
252 static const struct seq_operations tty_ldiscs_seq_ops = {
253 .start = tty_ldiscs_seq_start,
254 .next = tty_ldiscs_seq_next,
255 .stop = tty_ldiscs_seq_stop,
256 .show = tty_ldiscs_seq_show,
259 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
261 return seq_open(file, &tty_ldiscs_seq_ops);
264 const struct file_operations tty_ldiscs_proc_fops = {
265 .owner = THIS_MODULE,
266 .open = proc_tty_ldiscs_open,
269 .release = seq_release,
273 * tty_ldisc_assign - set ldisc on a tty
274 * @tty: tty to assign
275 * @ld: line discipline
277 * Install an instance of a line discipline into a tty structure. The
278 * ldisc must have a reference count above zero to ensure it remains.
279 * The tty instance refcount starts at zero.
282 * Caller must hold references
285 static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
291 * tty_ldisc_try - internal helper
294 * Make a single attempt to grab and bump the refcount on
295 * the tty ldisc. Return 0 on failure or 1 on success. This is
296 * used to implement both the waiting and non waiting versions
299 * Locking: takes tty_ldisc_lock
302 static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
305 struct tty_ldisc *ld;
307 spin_lock_irqsave(&tty_ldisc_lock, flags);
309 if (test_bit(TTY_LDISC, &tty->flags))
310 ld = get_ldisc(tty->ldisc);
311 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
316 * tty_ldisc_ref_wait - wait for the tty ldisc
319 * Dereference the line discipline for the terminal and take a
320 * reference to it. If the line discipline is in flux then
321 * wait patiently until it changes.
323 * Note: Must not be called from an IRQ/timer context. The caller
324 * must also be careful not to hold other locks that will deadlock
325 * against a discipline change, such as an existing ldisc reference
326 * (which we check for)
328 * Locking: call functions take tty_ldisc_lock
331 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
333 struct tty_ldisc *ld;
335 /* wait_event is a macro */
336 wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
339 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
342 * tty_ldisc_ref - get the tty ldisc
345 * Dereference the line discipline for the terminal and take a
346 * reference to it. If the line discipline is in flux then
347 * return NULL. Can be called from IRQ and timer functions.
349 * Locking: called functions take tty_ldisc_lock
352 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
354 return tty_ldisc_try(tty);
356 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
359 * tty_ldisc_deref - free a tty ldisc reference
360 * @ld: reference to free up
362 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
363 * be called in IRQ context.
365 * Locking: takes tty_ldisc_lock
368 void tty_ldisc_deref(struct tty_ldisc *ld)
372 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
374 static inline void tty_ldisc_put(struct tty_ldisc *ld)
380 * tty_ldisc_enable - allow ldisc use
381 * @tty: terminal to activate ldisc on
383 * Set the TTY_LDISC flag when the line discipline can be called
384 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
385 * changing flag to indicate any ldisc change is now over.
387 * Note: nobody should set the TTY_LDISC bit except via this function.
388 * Clearing directly is allowed.
391 void tty_ldisc_enable(struct tty_struct *tty)
393 set_bit(TTY_LDISC, &tty->flags);
394 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
395 wake_up(&tty_ldisc_wait);
399 * tty_ldisc_flush - flush line discipline queue
402 * Flush the line discipline queue (if any) for this tty. If there
403 * is no line discipline active this is a no-op.
406 void tty_ldisc_flush(struct tty_struct *tty)
408 struct tty_ldisc *ld = tty_ldisc_ref(tty);
410 if (ld->ops->flush_buffer)
411 ld->ops->flush_buffer(tty);
414 tty_buffer_flush(tty);
416 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
419 * tty_set_termios_ldisc - set ldisc field
420 * @tty: tty structure
421 * @num: line discipline number
423 * This is probably overkill for real world processors but
424 * they are not on hot paths so a little discipline won't do
427 * The line discipline-related tty_struct fields are reset to
428 * prevent the ldisc driver from re-using stale information for
429 * the new ldisc instance.
431 * Locking: takes termios_mutex
434 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
436 mutex_lock(&tty->termios_mutex);
437 tty->termios->c_line = num;
438 mutex_unlock(&tty->termios_mutex);
440 tty->disc_data = NULL;
441 tty->receive_room = 0;
445 * tty_ldisc_open - open a line discipline
446 * @tty: tty we are opening the ldisc on
447 * @ld: discipline to open
449 * A helper opening method. Also a convenient debugging and check
452 * Locking: always called with BTM already held.
455 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
457 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
460 /* BTM here locks versus a hangup event */
461 ret = ld->ops->open(tty);
463 clear_bit(TTY_LDISC_OPEN, &tty->flags);
470 * tty_ldisc_close - close a line discipline
471 * @tty: tty we are opening the ldisc on
472 * @ld: discipline to close
474 * A helper close method. Also a convenient debugging and check
478 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
480 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
481 clear_bit(TTY_LDISC_OPEN, &tty->flags);
487 * tty_ldisc_restore - helper for tty ldisc change
488 * @tty: tty to recover
489 * @old: previous ldisc
491 * Restore the previous line discipline or N_TTY when a line discipline
492 * change fails due to an open error
495 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
498 struct tty_ldisc *new_ldisc;
501 /* There is an outstanding reference here so this is safe */
502 old = tty_ldisc_get(old->ops->num);
503 WARN_ON(IS_ERR(old));
504 tty_ldisc_assign(tty, old);
505 tty_set_termios_ldisc(tty, old->ops->num);
506 if (tty_ldisc_open(tty, old) < 0) {
508 /* This driver is always present */
509 new_ldisc = tty_ldisc_get(N_TTY);
510 if (IS_ERR(new_ldisc))
512 tty_ldisc_assign(tty, new_ldisc);
513 tty_set_termios_ldisc(tty, N_TTY);
514 r = tty_ldisc_open(tty, new_ldisc);
516 panic("Couldn't open N_TTY ldisc for "
518 tty_name(tty, buf), r);
523 * tty_ldisc_halt - shut down the line discipline
526 * Shut down the line discipline and work queue for this tty device.
527 * The TTY_LDISC flag being cleared ensures no further references can
528 * be obtained while the delayed work queue halt ensures that no more
529 * data is fed to the ldisc.
531 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
532 * in order to make sure any currently executing ldisc work is also
536 static int tty_ldisc_halt(struct tty_struct *tty)
538 clear_bit(TTY_LDISC, &tty->flags);
539 return cancel_work_sync(&tty->buf.work);
543 * tty_ldisc_flush_works - flush all works of a tty
544 * @tty: tty device to flush works for
546 * Sync flush all works belonging to @tty.
548 static void tty_ldisc_flush_works(struct tty_struct *tty)
550 flush_work_sync(&tty->hangup_work);
551 flush_work_sync(&tty->SAK_work);
552 flush_work_sync(&tty->buf.work);
556 * tty_ldisc_wait_idle - wait for the ldisc to become idle
557 * @tty: tty to wait for
558 * @timeout: for how long to wait at most
560 * Wait for the line discipline to become idle. The discipline must
561 * have been halted for this to guarantee it remains idle.
563 static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
566 ret = wait_event_timeout(tty_ldisc_idle,
567 atomic_read(&tty->ldisc->users) == 1, timeout);
570 return ret > 0 ? 0 : -EBUSY;
574 * tty_set_ldisc - set line discipline
575 * @tty: the terminal to set
576 * @ldisc: the line discipline
578 * Set the discipline of a tty line. Must be called from a process
579 * context. The ldisc change logic has to protect itself against any
580 * overlapping ldisc change (including on the other end of pty pairs),
581 * the close of one side of a tty/pty pair, and eventually hangup.
583 * Locking: takes tty_ldisc_lock, termios_mutex
586 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
589 struct tty_ldisc *o_ldisc, *new_ldisc;
590 int work, o_work = 0;
591 struct tty_struct *o_tty;
593 new_ldisc = tty_ldisc_get(ldisc);
594 if (IS_ERR(new_ldisc))
595 return PTR_ERR(new_ldisc);
599 * We need to look at the tty locking here for pty/tty pairs
600 * when both sides try to change in parallel.
603 o_tty = tty->link; /* o_tty is the pty side or NULL */
607 * Check the no-op case
610 if (tty->ldisc->ops->num == ldisc) {
612 tty_ldisc_put(new_ldisc);
618 * Problem: What do we do if this blocks ?
619 * We could deadlock here
622 tty_wait_until_sent(tty, 0);
625 mutex_lock(&tty->ldisc_mutex);
628 * We could be midstream of another ldisc change which has
629 * dropped the lock during processing. If so we need to wait.
632 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
633 mutex_unlock(&tty->ldisc_mutex);
635 wait_event(tty_ldisc_wait,
636 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
638 mutex_lock(&tty->ldisc_mutex);
641 set_bit(TTY_LDISC_CHANGING, &tty->flags);
644 * No more input please, we are switching. The new ldisc
645 * will update this value in the ldisc open function
648 tty->receive_room = 0;
650 o_ldisc = tty->ldisc;
654 * Make sure we don't change while someone holds a
655 * reference to the line discipline. The TTY_LDISC bit
656 * prevents anyone taking a reference once it is clear.
657 * We need the lock to avoid racing reference takers.
659 * We must clear the TTY_LDISC bit here to avoid a livelock
660 * with a userspace app continually trying to use the tty in
661 * parallel to the change and re-referencing the tty.
664 work = tty_ldisc_halt(tty);
666 o_work = tty_ldisc_halt(o_tty);
669 * Wait for ->hangup_work and ->buf.work handlers to terminate.
670 * We must drop the mutex here in case a hangup is also in process.
673 mutex_unlock(&tty->ldisc_mutex);
675 tty_ldisc_flush_works(tty);
677 retval = tty_ldisc_wait_idle(tty, 5 * HZ);
680 mutex_lock(&tty->ldisc_mutex);
682 /* handle wait idle failure locked */
684 tty_ldisc_put(new_ldisc);
688 if (test_bit(TTY_HUPPED, &tty->flags)) {
689 /* We were raced by the hangup method. It will have stomped
690 the ldisc data and closed the ldisc down */
691 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
692 mutex_unlock(&tty->ldisc_mutex);
693 tty_ldisc_put(new_ldisc);
698 /* Shutdown the current discipline. */
699 tty_ldisc_close(tty, o_ldisc);
701 /* Now set up the new line discipline. */
702 tty_ldisc_assign(tty, new_ldisc);
703 tty_set_termios_ldisc(tty, ldisc);
705 retval = tty_ldisc_open(tty, new_ldisc);
707 /* Back to the old one or N_TTY if we can't */
708 tty_ldisc_put(new_ldisc);
709 tty_ldisc_restore(tty, o_ldisc);
712 /* At this point we hold a reference to the new ldisc and a
713 a reference to the old ldisc. If we ended up flipping back
714 to the existing ldisc we have two references to it */
716 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
717 tty->ops->set_ldisc(tty);
719 tty_ldisc_put(o_ldisc);
723 * Allow ldisc referencing to occur again
726 tty_ldisc_enable(tty);
728 tty_ldisc_enable(o_tty);
730 /* Restart the work queue in case no characters kick it off. Safe if
733 schedule_work(&tty->buf.work);
735 schedule_work(&o_tty->buf.work);
736 mutex_unlock(&tty->ldisc_mutex);
742 * tty_reset_termios - reset terminal state
745 * Restore a terminal to the driver default state.
748 static void tty_reset_termios(struct tty_struct *tty)
750 mutex_lock(&tty->termios_mutex);
751 *tty->termios = tty->driver->init_termios;
752 tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
753 tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
754 mutex_unlock(&tty->termios_mutex);
759 * tty_ldisc_reinit - reinitialise the tty ldisc
760 * @tty: tty to reinit
761 * @ldisc: line discipline to reinitialize
763 * Switch the tty to a line discipline and leave the ldisc
767 static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
769 struct tty_ldisc *ld = tty_ldisc_get(ldisc);
774 tty_ldisc_close(tty, tty->ldisc);
775 tty_ldisc_put(tty->ldisc);
778 * Switch the line discipline back
780 tty_ldisc_assign(tty, ld);
781 tty_set_termios_ldisc(tty, ldisc);
787 * tty_ldisc_hangup - hangup ldisc reset
788 * @tty: tty being hung up
790 * Some tty devices reset their termios when they receive a hangup
791 * event. In that situation we must also switch back to N_TTY properly
792 * before we reset the termios data.
794 * Locking: We can take the ldisc mutex as the rest of the code is
795 * careful to allow for this.
797 * In the pty pair case this occurs in the close() path of the
798 * tty itself so we must be careful about locking rules.
801 void tty_ldisc_hangup(struct tty_struct *tty)
803 struct tty_ldisc *ld;
804 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
808 * FIXME! What are the locking issues here? This may me overdoing
809 * things... This question is especially important now that we've
810 * removed the irqlock.
812 ld = tty_ldisc_ref(tty);
814 /* We may have no line discipline at this point */
815 if (ld->ops->flush_buffer)
816 ld->ops->flush_buffer(tty);
817 tty_driver_flush_buffer(tty);
818 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
819 ld->ops->write_wakeup)
820 ld->ops->write_wakeup(tty);
822 ld->ops->hangup(tty);
826 * FIXME: Once we trust the LDISC code better we can wait here for
827 * ldisc completion and fix the driver call race
829 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
830 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
832 * Shutdown the current line discipline, and reset it to
835 * Avoid racing set_ldisc or tty_ldisc_release
837 mutex_lock(&tty->ldisc_mutex);
840 * this is like tty_ldisc_halt, but we need to give up
841 * the BTM before calling cancel_work_sync, which may
842 * need to wait for another function taking the BTM
844 clear_bit(TTY_LDISC, &tty->flags);
846 cancel_work_sync(&tty->buf.work);
847 mutex_unlock(&tty->ldisc_mutex);
850 mutex_lock(&tty->ldisc_mutex);
852 /* At this point we have a closed ldisc and we want to
853 reopen it. We could defer this to the next open but
854 it means auditing a lot of other paths so this is
856 if (tty->ldisc) { /* Not yet closed */
857 if (atomic_read(&tty->ldisc->users) != 1) {
858 char cur_n[TASK_COMM_LEN], tty_n[64];
859 long timeout = 3 * HZ;
862 while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
863 timeout = MAX_SCHEDULE_TIMEOUT;
864 printk_ratelimited(KERN_WARNING
865 "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
866 __func__, get_task_comm(cur_n, current),
867 tty_name(tty, tty_n));
869 mutex_unlock(&tty->ldisc_mutex);
875 if (!tty_ldisc_reinit(tty, tty->termios->c_line))
876 err = tty_ldisc_open(tty, tty->ldisc);
880 /* If the re-open fails or we reset then go to N_TTY. The
881 N_TTY open cannot fail */
883 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
884 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
886 tty_ldisc_enable(tty);
888 mutex_unlock(&tty->ldisc_mutex);
890 tty_reset_termios(tty);
894 * tty_ldisc_setup - open line discipline
895 * @tty: tty being shut down
896 * @o_tty: pair tty for pty/tty pairs
898 * Called during the initial open of a tty/pty pair in order to set up the
899 * line disciplines and bind them to the tty. This has no locking issues
900 * as the device isn't yet active.
903 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
905 struct tty_ldisc *ld = tty->ldisc;
908 retval = tty_ldisc_open(tty, ld);
913 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
915 tty_ldisc_close(tty, ld);
918 tty_ldisc_enable(o_tty);
920 tty_ldisc_enable(tty);
924 * tty_ldisc_release - release line discipline
925 * @tty: tty being shut down
926 * @o_tty: pair tty for pty/tty pairs
928 * Called during the final close of a tty/pty pair in order to shut down
929 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
930 * ldisc has not been opened.
933 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
936 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
937 * kill any delayed work. As this is the final close it does not
938 * race with the set_ldisc code path.
943 tty_ldisc_flush_works(tty);
946 mutex_lock(&tty->ldisc_mutex);
948 * Now kill off the ldisc
950 tty_ldisc_close(tty, tty->ldisc);
951 tty_ldisc_put(tty->ldisc);
952 /* Force an oops if we mess this up */
955 /* Ensure the next open requests the N_TTY ldisc */
956 tty_set_termios_ldisc(tty, N_TTY);
957 mutex_unlock(&tty->ldisc_mutex);
959 /* This will need doing differently if we need to lock */
961 tty_ldisc_release(o_tty, NULL);
963 /* And the memory resources remaining (buffers, termios) will be
964 disposed of when the kref hits zero */
968 * tty_ldisc_init - ldisc setup for new tty
969 * @tty: tty being allocated
971 * Set up the line discipline objects for a newly allocated tty. Note that
972 * the tty structure is not completely set up when this call is made.
975 void tty_ldisc_init(struct tty_struct *tty)
977 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
979 panic("n_tty: init_tty");
980 tty_ldisc_assign(tty, ld);
984 * tty_ldisc_init - ldisc cleanup for new tty
985 * @tty: tty that was allocated recently
987 * The tty structure must not becompletely set up (tty_ldisc_setup) when
990 void tty_ldisc_deinit(struct tty_struct *tty)
992 put_ldisc(tty->ldisc);
993 tty_ldisc_assign(tty, NULL);
996 void tty_ldisc_begin(void)
998 /* Setup the default TTY line discipline. */
999 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);