1 #include <linux/types.h>
2 #include <linux/errno.h>
3 #include <linux/kmod.h>
4 #include <linux/sched.h>
5 #include <linux/interrupt.h>
7 #include <linux/tty_driver.h>
8 #include <linux/file.h>
10 #include <linux/string.h>
11 #include <linux/slab.h>
12 #include <linux/poll.h>
13 #include <linux/proc_fs.h>
14 #include <linux/init.h>
15 #include <linux/module.h>
16 #include <linux/device.h>
17 #include <linux/wait.h>
18 #include <linux/bitops.h>
19 #include <linux/seq_file.h>
20 #include <linux/uaccess.h>
21 #include <linux/ratelimit.h>
23 #undef LDISC_DEBUG_HANGUP
25 #ifdef LDISC_DEBUG_HANGUP
26 #define tty_ldisc_debug(tty, f, args...) ({ \
28 printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
31 #define tty_ldisc_debug(tty, f, args...)
35 * This guards the refcounted line discipline lists. The lock
36 * must be taken with irqs off because there are hangup path
37 * callers who will do ldisc lookups and cannot sleep.
40 static DEFINE_RAW_SPINLOCK(tty_ldisc_lock);
41 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
42 /* Line disc dispatch table */
43 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
45 static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
48 atomic_inc(&ld->users);
53 * tty_register_ldisc - install a line discipline
55 * @new_ldisc: pointer to the ldisc object
57 * Installs a new line discipline into the kernel. The discipline
58 * is set up as unreferenced and then made available to the kernel
59 * from this point onwards.
62 * takes tty_ldisc_lock to guard against ldisc races
65 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
70 if (disc < N_TTY || disc >= NR_LDISCS)
73 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
74 tty_ldiscs[disc] = new_ldisc;
75 new_ldisc->num = disc;
76 new_ldisc->refcount = 0;
77 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
81 EXPORT_SYMBOL(tty_register_ldisc);
84 * tty_unregister_ldisc - unload a line discipline
86 * @new_ldisc: pointer to the ldisc object
88 * Remove a line discipline from the kernel providing it is not
92 * takes tty_ldisc_lock to guard against ldisc races
95 int tty_unregister_ldisc(int disc)
100 if (disc < N_TTY || disc >= NR_LDISCS)
103 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
104 if (tty_ldiscs[disc]->refcount)
107 tty_ldiscs[disc] = NULL;
108 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
112 EXPORT_SYMBOL(tty_unregister_ldisc);
114 static struct tty_ldisc_ops *get_ldops(int disc)
117 struct tty_ldisc_ops *ldops, *ret;
119 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
120 ret = ERR_PTR(-EINVAL);
121 ldops = tty_ldiscs[disc];
123 ret = ERR_PTR(-EAGAIN);
124 if (try_module_get(ldops->owner)) {
129 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
133 static void put_ldops(struct tty_ldisc_ops *ldops)
137 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
139 module_put(ldops->owner);
140 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
144 * tty_ldisc_get - take a reference to an ldisc
145 * @disc: ldisc number
147 * Takes a reference to a line discipline. Deals with refcounts and
148 * module locking counts. Returns NULL if the discipline is not available.
149 * Returns a pointer to the discipline and bumps the ref count if it is
153 * takes tty_ldisc_lock to guard against ldisc races
156 static struct tty_ldisc *tty_ldisc_get(int disc)
158 struct tty_ldisc *ld;
159 struct tty_ldisc_ops *ldops;
161 if (disc < N_TTY || disc >= NR_LDISCS)
162 return ERR_PTR(-EINVAL);
165 * Get the ldisc ops - we may need to request them to be loaded
166 * dynamically and try again.
168 ldops = get_ldops(disc);
170 request_module("tty-ldisc-%d", disc);
171 ldops = get_ldops(disc);
173 return ERR_CAST(ldops);
176 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
179 return ERR_PTR(-ENOMEM);
183 atomic_set(&ld->users, 1);
184 init_waitqueue_head(&ld->wq_idle);
189 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
191 return (*pos < NR_LDISCS) ? pos : NULL;
194 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
197 return (*pos < NR_LDISCS) ? pos : NULL;
200 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
204 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
206 int i = *(loff_t *)v;
207 struct tty_ldisc_ops *ldops;
209 ldops = get_ldops(i);
212 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
217 static const struct seq_operations tty_ldiscs_seq_ops = {
218 .start = tty_ldiscs_seq_start,
219 .next = tty_ldiscs_seq_next,
220 .stop = tty_ldiscs_seq_stop,
221 .show = tty_ldiscs_seq_show,
224 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
226 return seq_open(file, &tty_ldiscs_seq_ops);
229 const struct file_operations tty_ldiscs_proc_fops = {
230 .owner = THIS_MODULE,
231 .open = proc_tty_ldiscs_open,
234 .release = seq_release,
238 * tty_ldisc_assign - set ldisc on a tty
239 * @tty: tty to assign
240 * @ld: line discipline
242 * Install an instance of a line discipline into a tty structure. The
243 * ldisc must have a reference count above zero to ensure it remains.
244 * The tty instance refcount starts at zero.
247 * Caller must hold references
250 static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
256 * tty_ldisc_try - internal helper
259 * Make a single attempt to grab and bump the refcount on
260 * the tty ldisc. Return 0 on failure or 1 on success. This is
261 * used to implement both the waiting and non waiting versions
264 * Locking: takes tty_ldisc_lock
267 static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
270 struct tty_ldisc *ld;
272 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
274 if (test_bit(TTY_LDISC, &tty->flags))
275 ld = get_ldisc(tty->ldisc);
276 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
281 * tty_ldisc_ref_wait - wait for the tty ldisc
284 * Dereference the line discipline for the terminal and take a
285 * reference to it. If the line discipline is in flux then
286 * wait patiently until it changes.
288 * Note: Must not be called from an IRQ/timer context. The caller
289 * must also be careful not to hold other locks that will deadlock
290 * against a discipline change, such as an existing ldisc reference
291 * (which we check for)
293 * Locking: call functions take tty_ldisc_lock
296 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
298 struct tty_ldisc *ld;
300 /* wait_event is a macro */
301 wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
304 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
307 * tty_ldisc_ref - get the tty ldisc
310 * Dereference the line discipline for the terminal and take a
311 * reference to it. If the line discipline is in flux then
312 * return NULL. Can be called from IRQ and timer functions.
314 * Locking: called functions take tty_ldisc_lock
317 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
319 return tty_ldisc_try(tty);
321 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
324 * tty_ldisc_deref - free a tty ldisc reference
325 * @ld: reference to free up
327 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
328 * be called in IRQ context.
330 * Locking: takes tty_ldisc_lock
333 void tty_ldisc_deref(struct tty_ldisc *ld)
337 if (WARN_ON_ONCE(!ld))
340 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
342 * WARNs if one-too-many reader references were released
343 * - the last reference must be released with tty_ldisc_put
345 WARN_ON(atomic_dec_and_test(&ld->users));
346 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
348 if (waitqueue_active(&ld->wq_idle))
349 wake_up(&ld->wq_idle);
351 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
354 * tty_ldisc_put - release the ldisc
356 * Complement of tty_ldisc_get().
358 static inline void tty_ldisc_put(struct tty_ldisc *ld)
362 if (WARN_ON_ONCE(!ld))
365 raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
367 /* unreleased reader reference(s) will cause this WARN */
368 WARN_ON(!atomic_dec_and_test(&ld->users));
371 module_put(ld->ops->owner);
373 raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
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 static void tty_ldisc_enable(struct tty_struct *tty)
390 clear_bit(TTY_LDISC_HALTED, &tty->flags);
391 set_bit(TTY_LDISC, &tty->flags);
392 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
393 wake_up(&tty_ldisc_wait);
397 * tty_ldisc_flush - flush line discipline queue
400 * Flush the line discipline queue (if any) for this tty. If there
401 * is no line discipline active this is a no-op.
404 void tty_ldisc_flush(struct tty_struct *tty)
406 struct tty_ldisc *ld = tty_ldisc_ref(tty);
408 if (ld->ops->flush_buffer)
409 ld->ops->flush_buffer(tty);
412 tty_buffer_flush(tty);
414 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
417 * tty_set_termios_ldisc - set ldisc field
418 * @tty: tty structure
419 * @num: line discipline number
421 * This is probably overkill for real world processors but
422 * they are not on hot paths so a little discipline won't do
425 * Locking: takes termios_mutex
428 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
430 mutex_lock(&tty->termios_mutex);
431 tty->termios.c_line = num;
432 mutex_unlock(&tty->termios_mutex);
436 * tty_ldisc_open - open a line discipline
437 * @tty: tty we are opening the ldisc on
438 * @ld: discipline to open
440 * A helper opening method. Also a convenient debugging and check
443 * Locking: always called with BTM already held.
446 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
448 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
451 /* BTM here locks versus a hangup event */
452 ret = ld->ops->open(tty);
454 clear_bit(TTY_LDISC_OPEN, &tty->flags);
461 * tty_ldisc_close - close a line discipline
462 * @tty: tty we are opening the ldisc on
463 * @ld: discipline to close
465 * A helper close method. Also a convenient debugging and check
469 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
471 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
472 clear_bit(TTY_LDISC_OPEN, &tty->flags);
478 * tty_ldisc_restore - helper for tty ldisc change
479 * @tty: tty to recover
480 * @old: previous ldisc
482 * Restore the previous line discipline or N_TTY when a line discipline
483 * change fails due to an open error
486 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
489 struct tty_ldisc *new_ldisc;
492 /* There is an outstanding reference here so this is safe */
493 old = tty_ldisc_get(old->ops->num);
494 WARN_ON(IS_ERR(old));
495 tty_ldisc_assign(tty, old);
496 tty_set_termios_ldisc(tty, old->ops->num);
497 if (tty_ldisc_open(tty, old) < 0) {
499 /* This driver is always present */
500 new_ldisc = tty_ldisc_get(N_TTY);
501 if (IS_ERR(new_ldisc))
503 tty_ldisc_assign(tty, new_ldisc);
504 tty_set_termios_ldisc(tty, N_TTY);
505 r = tty_ldisc_open(tty, new_ldisc);
507 panic("Couldn't open N_TTY ldisc for "
509 tty_name(tty, buf), r);
514 * tty_ldisc_wait_idle - wait for the ldisc to become idle
515 * @tty: tty to wait for
516 * @timeout: for how long to wait at most
518 * Wait for the line discipline to become idle. The discipline must
519 * have been halted for this to guarantee it remains idle.
521 static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
524 ret = wait_event_timeout(tty->ldisc->wq_idle,
525 atomic_read(&tty->ldisc->users) == 1, timeout);
526 return ret > 0 ? 0 : -EBUSY;
530 * tty_ldisc_halt - shut down the line discipline
532 * @o_tty: paired pty device (can be NULL)
533 * @timeout: # of jiffies to wait for ldisc refs to be released
535 * Shut down the line discipline and work queue for this tty device and
536 * its paired pty (if exists). Clearing the TTY_LDISC flag ensures
537 * no further references can be obtained, while waiting for existing
538 * references to be released ensures no more data is fed to the ldisc.
540 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
541 * in order to make sure any currently executing ldisc work is also
545 static int tty_ldisc_halt(struct tty_struct *tty, struct tty_struct *o_tty,
550 clear_bit(TTY_LDISC, &tty->flags);
552 clear_bit(TTY_LDISC, &o_tty->flags);
554 retval = tty_ldisc_wait_idle(tty, timeout);
555 if (!retval && o_tty)
556 retval = tty_ldisc_wait_idle(o_tty, timeout);
560 set_bit(TTY_LDISC_HALTED, &tty->flags);
562 set_bit(TTY_LDISC_HALTED, &o_tty->flags);
568 * tty_ldisc_hangup_halt - halt the line discipline for hangup
569 * @tty: tty being hung up
571 * Shut down the line discipline and work queue for the tty device
572 * being hungup. Clear the TTY_LDISC flag to ensure no further
573 * references can be obtained and wait for remaining references to be
574 * released to ensure no more data is fed to this ldisc.
575 * Caller must hold legacy and ->ldisc_mutex.
577 * NB: tty_set_ldisc() is prevented from changing the ldisc concurrently
578 * with this function by checking the TTY_HUPPING flag.
580 static bool tty_ldisc_hangup_halt(struct tty_struct *tty)
582 char cur_n[TASK_COMM_LEN], tty_n[64];
583 long timeout = 3 * HZ;
585 clear_bit(TTY_LDISC, &tty->flags);
587 if (tty->ldisc) { /* Not yet closed */
590 while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
591 timeout = MAX_SCHEDULE_TIMEOUT;
592 printk_ratelimited(KERN_WARNING
593 "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
594 __func__, get_task_comm(cur_n, current),
595 tty_name(tty, tty_n));
598 set_bit(TTY_LDISC_HALTED, &tty->flags);
600 /* must reacquire both locks and preserve lock order */
601 mutex_unlock(&tty->ldisc_mutex);
603 mutex_lock(&tty->ldisc_mutex);
609 * tty_set_ldisc - set line discipline
610 * @tty: the terminal to set
611 * @ldisc: the line discipline
613 * Set the discipline of a tty line. Must be called from a process
614 * context. The ldisc change logic has to protect itself against any
615 * overlapping ldisc change (including on the other end of pty pairs),
616 * the close of one side of a tty/pty pair, and eventually hangup.
618 * Locking: takes tty_ldisc_lock, termios_mutex
621 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
624 struct tty_ldisc *o_ldisc, *new_ldisc;
625 struct tty_struct *o_tty;
627 new_ldisc = tty_ldisc_get(ldisc);
628 if (IS_ERR(new_ldisc))
629 return PTR_ERR(new_ldisc);
633 * We need to look at the tty locking here for pty/tty pairs
634 * when both sides try to change in parallel.
637 o_tty = tty->link; /* o_tty is the pty side or NULL */
641 * Check the no-op case
644 if (tty->ldisc->ops->num == ldisc) {
646 tty_ldisc_put(new_ldisc);
652 * Problem: What do we do if this blocks ?
653 * We could deadlock here
656 tty_wait_until_sent(tty, 0);
659 mutex_lock(&tty->ldisc_mutex);
662 * We could be midstream of another ldisc change which has
663 * dropped the lock during processing. If so we need to wait.
666 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
667 mutex_unlock(&tty->ldisc_mutex);
669 wait_event(tty_ldisc_wait,
670 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
672 mutex_lock(&tty->ldisc_mutex);
675 set_bit(TTY_LDISC_CHANGING, &tty->flags);
678 * No more input please, we are switching. The new ldisc
679 * will update this value in the ldisc open function
682 tty->receive_room = 0;
684 o_ldisc = tty->ldisc;
688 * Make sure we don't change while someone holds a
689 * reference to the line discipline. The TTY_LDISC bit
690 * prevents anyone taking a reference once it is clear.
691 * We need the lock to avoid racing reference takers.
693 * We must clear the TTY_LDISC bit here to avoid a livelock
694 * with a userspace app continually trying to use the tty in
695 * parallel to the change and re-referencing the tty.
698 retval = tty_ldisc_halt(tty, o_tty, 5 * HZ);
701 * Wait for hangup to complete, if pending.
702 * We must drop the mutex here in case a hangup is also in process.
705 mutex_unlock(&tty->ldisc_mutex);
707 flush_work(&tty->hangup_work);
710 mutex_lock(&tty->ldisc_mutex);
712 /* handle wait idle failure locked */
714 tty_ldisc_put(new_ldisc);
718 if (test_bit(TTY_HUPPING, &tty->flags)) {
719 /* We were raced by the hangup method. It will have stomped
720 the ldisc data and closed the ldisc down */
721 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
722 mutex_unlock(&tty->ldisc_mutex);
723 tty_ldisc_put(new_ldisc);
728 /* Shutdown the current discipline. */
729 tty_ldisc_close(tty, o_ldisc);
731 /* Now set up the new line discipline. */
732 tty_ldisc_assign(tty, new_ldisc);
733 tty_set_termios_ldisc(tty, ldisc);
735 retval = tty_ldisc_open(tty, new_ldisc);
737 /* Back to the old one or N_TTY if we can't */
738 tty_ldisc_put(new_ldisc);
739 tty_ldisc_restore(tty, o_ldisc);
742 /* At this point we hold a reference to the new ldisc and a
743 a reference to the old ldisc. If we ended up flipping back
744 to the existing ldisc we have two references to it */
746 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
747 tty->ops->set_ldisc(tty);
749 tty_ldisc_put(o_ldisc);
753 * Allow ldisc referencing to occur again
756 tty_ldisc_enable(tty);
758 tty_ldisc_enable(o_tty);
760 /* Restart the work queue in case no characters kick it off. Safe if
762 schedule_work(&tty->port->buf.work);
764 schedule_work(&o_tty->port->buf.work);
766 mutex_unlock(&tty->ldisc_mutex);
772 * tty_reset_termios - reset terminal state
775 * Restore a terminal to the driver default state.
778 static void tty_reset_termios(struct tty_struct *tty)
780 mutex_lock(&tty->termios_mutex);
781 tty->termios = tty->driver->init_termios;
782 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
783 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
784 mutex_unlock(&tty->termios_mutex);
789 * tty_ldisc_reinit - reinitialise the tty ldisc
790 * @tty: tty to reinit
791 * @ldisc: line discipline to reinitialize
793 * Switch the tty to a line discipline and leave the ldisc
797 static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
799 struct tty_ldisc *ld = tty_ldisc_get(ldisc);
804 tty_ldisc_close(tty, tty->ldisc);
805 tty_ldisc_put(tty->ldisc);
808 * Switch the line discipline back
810 tty_ldisc_assign(tty, ld);
811 tty_set_termios_ldisc(tty, ldisc);
817 * tty_ldisc_hangup - hangup ldisc reset
818 * @tty: tty being hung up
820 * Some tty devices reset their termios when they receive a hangup
821 * event. In that situation we must also switch back to N_TTY properly
822 * before we reset the termios data.
824 * Locking: We can take the ldisc mutex as the rest of the code is
825 * careful to allow for this.
827 * In the pty pair case this occurs in the close() path of the
828 * tty itself so we must be careful about locking rules.
831 void tty_ldisc_hangup(struct tty_struct *tty)
833 struct tty_ldisc *ld;
834 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
837 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
840 * FIXME! What are the locking issues here? This may me overdoing
841 * things... This question is especially important now that we've
842 * removed the irqlock.
844 ld = tty_ldisc_ref(tty);
846 /* We may have no line discipline at this point */
847 if (ld->ops->flush_buffer)
848 ld->ops->flush_buffer(tty);
849 tty_driver_flush_buffer(tty);
850 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
851 ld->ops->write_wakeup)
852 ld->ops->write_wakeup(tty);
854 ld->ops->hangup(tty);
858 * FIXME: Once we trust the LDISC code better we can wait here for
859 * ldisc completion and fix the driver call race
861 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
862 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
864 * Shutdown the current line discipline, and reset it to
867 * Avoid racing set_ldisc or tty_ldisc_release
869 mutex_lock(&tty->ldisc_mutex);
871 if (tty_ldisc_hangup_halt(tty)) {
873 /* At this point we have a halted ldisc; we want to close it and
874 reopen a new ldisc. We could defer the reopen to the next
875 open but it means auditing a lot of other paths so this is
879 if (!tty_ldisc_reinit(tty, tty->termios.c_line))
880 err = tty_ldisc_open(tty, tty->ldisc);
884 /* If the re-open fails or we reset then go to N_TTY. The
885 N_TTY open cannot fail */
887 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
888 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
890 tty_ldisc_enable(tty);
892 mutex_unlock(&tty->ldisc_mutex);
894 tty_reset_termios(tty);
896 tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc);
900 * tty_ldisc_setup - open line discipline
901 * @tty: tty being shut down
902 * @o_tty: pair tty for pty/tty pairs
904 * Called during the initial open of a tty/pty pair in order to set up the
905 * line disciplines and bind them to the tty. This has no locking issues
906 * as the device isn't yet active.
909 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
911 struct tty_ldisc *ld = tty->ldisc;
914 retval = tty_ldisc_open(tty, ld);
919 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
921 tty_ldisc_close(tty, ld);
924 tty_ldisc_enable(o_tty);
926 tty_ldisc_enable(tty);
930 static void tty_ldisc_kill(struct tty_struct *tty)
932 mutex_lock(&tty->ldisc_mutex);
934 * Now kill off the ldisc
936 tty_ldisc_close(tty, tty->ldisc);
937 tty_ldisc_put(tty->ldisc);
938 /* Force an oops if we mess this up */
941 /* Ensure the next open requests the N_TTY ldisc */
942 tty_set_termios_ldisc(tty, N_TTY);
943 mutex_unlock(&tty->ldisc_mutex);
947 * tty_ldisc_release - release line discipline
948 * @tty: tty being shut down
949 * @o_tty: pair tty for pty/tty pairs
951 * Called during the final close of a tty/pty pair in order to shut down
952 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
953 * ldisc has not been opened.
956 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
959 * Shutdown this line discipline. As this is the final close,
960 * it does not race with the set_ldisc code path.
963 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
965 tty_ldisc_halt(tty, o_tty, MAX_SCHEDULE_TIMEOUT);
967 tty_lock_pair(tty, o_tty);
968 /* This will need doing differently if we need to lock */
971 tty_ldisc_kill(o_tty);
973 tty_unlock_pair(tty, o_tty);
974 /* And the memory resources remaining (buffers, termios) will be
975 disposed of when the kref hits zero */
977 tty_ldisc_debug(tty, "ldisc closed\n");
981 * tty_ldisc_init - ldisc setup for new tty
982 * @tty: tty being allocated
984 * Set up the line discipline objects for a newly allocated tty. Note that
985 * the tty structure is not completely set up when this call is made.
988 void tty_ldisc_init(struct tty_struct *tty)
990 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
992 panic("n_tty: init_tty");
993 tty_ldisc_assign(tty, ld);
997 * tty_ldisc_init - ldisc cleanup for new tty
998 * @tty: tty that was allocated recently
1000 * The tty structure must not becompletely set up (tty_ldisc_setup) when
1001 * this call is made.
1003 void tty_ldisc_deinit(struct tty_struct *tty)
1005 tty_ldisc_put(tty->ldisc);
1006 tty_ldisc_assign(tty, NULL);
1009 void tty_ldisc_begin(void)
1011 /* Setup the default TTY line discipline. */
1012 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);