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/module.h>
15 #include <linux/device.h>
16 #include <linux/wait.h>
17 #include <linux/bitops.h>
18 #include <linux/seq_file.h>
19 #include <linux/uaccess.h>
20 #include <linux/ratelimit.h>
22 #undef LDISC_DEBUG_HANGUP
24 #ifdef LDISC_DEBUG_HANGUP
25 #define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
27 #define tty_ldisc_debug(tty, f, args...)
30 /* lockdep nested classes for tty->ldisc_sem */
38 * This guards the refcounted line discipline lists. The lock
39 * must be taken with irqs off because there are hangup path
40 * callers who will do ldisc lookups and cannot sleep.
43 static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
44 /* Line disc dispatch table */
45 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
48 * tty_register_ldisc - install a line discipline
50 * @new_ldisc: pointer to the ldisc object
52 * Installs a new line discipline into the kernel. The discipline
53 * is set up as unreferenced and then made available to the kernel
54 * from this point onwards.
57 * takes tty_ldiscs_lock to guard against ldisc races
60 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
65 if (disc < N_TTY || disc >= NR_LDISCS)
68 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
69 tty_ldiscs[disc] = new_ldisc;
70 new_ldisc->num = disc;
71 new_ldisc->refcount = 0;
72 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
76 EXPORT_SYMBOL(tty_register_ldisc);
79 * tty_unregister_ldisc - unload a line discipline
81 * @new_ldisc: pointer to the ldisc object
83 * Remove a line discipline from the kernel providing it is not
87 * takes tty_ldiscs_lock to guard against ldisc races
90 int tty_unregister_ldisc(int disc)
95 if (disc < N_TTY || disc >= NR_LDISCS)
98 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
99 if (tty_ldiscs[disc]->refcount)
102 tty_ldiscs[disc] = NULL;
103 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107 EXPORT_SYMBOL(tty_unregister_ldisc);
109 static struct tty_ldisc_ops *get_ldops(int disc)
112 struct tty_ldisc_ops *ldops, *ret;
114 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115 ret = ERR_PTR(-EINVAL);
116 ldops = tty_ldiscs[disc];
118 ret = ERR_PTR(-EAGAIN);
119 if (try_module_get(ldops->owner)) {
124 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
128 static void put_ldops(struct tty_ldisc_ops *ldops)
132 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
134 module_put(ldops->owner);
135 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
139 * tty_ldisc_get - take a reference to an ldisc
140 * @disc: ldisc number
142 * Takes a reference to a line discipline. Deals with refcounts and
143 * module locking counts. Returns NULL if the discipline is not available.
144 * Returns a pointer to the discipline and bumps the ref count if it is
148 * takes tty_ldiscs_lock to guard against ldisc races
151 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
153 struct tty_ldisc *ld;
154 struct tty_ldisc_ops *ldops;
156 if (disc < N_TTY || disc >= NR_LDISCS)
157 return ERR_PTR(-EINVAL);
160 * Get the ldisc ops - we may need to request them to be loaded
161 * dynamically and try again.
163 ldops = get_ldops(disc);
165 request_module("tty-ldisc-%d", disc);
166 ldops = get_ldops(disc);
168 return ERR_CAST(ldops);
171 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
174 return ERR_PTR(-ENOMEM);
184 * tty_ldisc_put - release the ldisc
186 * Complement of tty_ldisc_get().
188 static void tty_ldisc_put(struct tty_ldisc *ld)
190 if (WARN_ON_ONCE(!ld))
197 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
199 return (*pos < NR_LDISCS) ? pos : NULL;
202 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
205 return (*pos < NR_LDISCS) ? pos : NULL;
208 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
212 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
214 int i = *(loff_t *)v;
215 struct tty_ldisc_ops *ldops;
217 ldops = get_ldops(i);
220 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
225 static const struct seq_operations tty_ldiscs_seq_ops = {
226 .start = tty_ldiscs_seq_start,
227 .next = tty_ldiscs_seq_next,
228 .stop = tty_ldiscs_seq_stop,
229 .show = tty_ldiscs_seq_show,
232 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
234 return seq_open(file, &tty_ldiscs_seq_ops);
237 const struct file_operations tty_ldiscs_proc_fops = {
238 .owner = THIS_MODULE,
239 .open = proc_tty_ldiscs_open,
242 .release = seq_release,
246 * tty_ldisc_ref_wait - wait for the tty ldisc
249 * Dereference the line discipline for the terminal and take a
250 * reference to it. If the line discipline is in flux then
251 * wait patiently until it changes.
253 * Note: Must not be called from an IRQ/timer context. The caller
254 * must also be careful not to hold other locks that will deadlock
255 * against a discipline change, such as an existing ldisc reference
256 * (which we check for)
258 * Note: only callable from a file_operations routine (which
259 * guarantees tty->ldisc != NULL when the lock is acquired).
262 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
264 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
265 WARN_ON(!tty->ldisc);
268 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
271 * tty_ldisc_ref - get the tty ldisc
274 * Dereference the line discipline for the terminal and take a
275 * reference to it. If the line discipline is in flux then
276 * return NULL. Can be called from IRQ and timer functions.
279 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
281 struct tty_ldisc *ld = NULL;
283 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
286 ldsem_up_read(&tty->ldisc_sem);
290 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
293 * tty_ldisc_deref - free a tty ldisc reference
294 * @ld: reference to free up
296 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
297 * be called in IRQ context.
300 void tty_ldisc_deref(struct tty_ldisc *ld)
302 ldsem_up_read(&ld->tty->ldisc_sem);
304 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
308 __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
310 return ldsem_down_write(&tty->ldisc_sem, timeout);
314 __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
316 return ldsem_down_write_nested(&tty->ldisc_sem,
317 LDISC_SEM_OTHER, timeout);
320 static inline void __tty_ldisc_unlock(struct tty_struct *tty)
322 ldsem_up_write(&tty->ldisc_sem);
325 static int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
329 ret = __tty_ldisc_lock(tty, timeout);
332 set_bit(TTY_LDISC_HALTED, &tty->flags);
336 static void tty_ldisc_unlock(struct tty_struct *tty)
338 clear_bit(TTY_LDISC_HALTED, &tty->flags);
339 __tty_ldisc_unlock(tty);
343 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
344 unsigned long timeout)
349 ret = __tty_ldisc_lock(tty, timeout);
351 ret = __tty_ldisc_lock_nested(tty2, timeout);
353 __tty_ldisc_unlock(tty);
356 /* if this is possible, it has lots of implications */
357 WARN_ON_ONCE(tty == tty2);
358 if (tty2 && tty != tty2) {
359 ret = __tty_ldisc_lock(tty2, timeout);
361 ret = __tty_ldisc_lock_nested(tty, timeout);
363 __tty_ldisc_unlock(tty2);
366 ret = __tty_ldisc_lock(tty, timeout);
372 set_bit(TTY_LDISC_HALTED, &tty->flags);
374 set_bit(TTY_LDISC_HALTED, &tty2->flags);
378 static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
380 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
383 static void tty_ldisc_unlock_pair(struct tty_struct *tty,
384 struct tty_struct *tty2)
386 __tty_ldisc_unlock(tty);
388 __tty_ldisc_unlock(tty2);
392 * tty_ldisc_flush - flush line discipline queue
395 * Flush the line discipline queue (if any) and the tty flip buffers
399 void tty_ldisc_flush(struct tty_struct *tty)
401 struct tty_ldisc *ld = tty_ldisc_ref(tty);
403 tty_buffer_flush(tty, ld);
407 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
410 * tty_set_termios_ldisc - set ldisc field
411 * @tty: tty structure
412 * @num: line discipline number
414 * This is probably overkill for real world processors but
415 * they are not on hot paths so a little discipline won't do
418 * The line discipline-related tty_struct fields are reset to
419 * prevent the ldisc driver from re-using stale information for
420 * the new ldisc instance.
422 * Locking: takes termios_rwsem
425 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
427 down_write(&tty->termios_rwsem);
428 tty->termios.c_line = num;
429 up_write(&tty->termios_rwsem);
431 tty->disc_data = NULL;
432 tty->receive_room = 0;
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);
456 tty_ldisc_debug(tty, "%p: opened\n", tty->ldisc);
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);
477 tty_ldisc_debug(tty, "%p: closed\n", tty->ldisc);
481 * tty_ldisc_restore - helper for tty ldisc change
482 * @tty: tty to recover
483 * @old: previous ldisc
485 * Restore the previous line discipline or N_TTY when a line discipline
486 * change fails due to an open error
489 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(tty, old->ops->num);
496 WARN_ON(IS_ERR(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(tty, N_TTY);
503 if (IS_ERR(new_ldisc))
505 tty->ldisc = 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 "
516 * tty_set_ldisc - set line discipline
517 * @tty: the terminal to set
518 * @ldisc: the line discipline
520 * Set the discipline of a tty line. Must be called from a process
521 * context. The ldisc change logic has to protect itself against any
522 * overlapping ldisc change (including on the other end of pty pairs),
523 * the close of one side of a tty/pty pair, and eventually hangup.
526 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
529 struct tty_ldisc *old_ldisc, *new_ldisc;
531 new_ldisc = tty_ldisc_get(tty, ldisc);
532 if (IS_ERR(new_ldisc))
533 return PTR_ERR(new_ldisc);
536 retval = tty_ldisc_lock(tty, 5 * HZ);
540 /* Check the no-op case */
541 if (tty->ldisc->ops->num == ldisc)
544 if (test_bit(TTY_HUPPED, &tty->flags)) {
545 /* We were raced by hangup */
550 old_ldisc = tty->ldisc;
552 /* Shutdown the old discipline. */
553 tty_ldisc_close(tty, old_ldisc);
555 /* Now set up the new line discipline. */
556 tty->ldisc = new_ldisc;
557 tty_set_termios_ldisc(tty, ldisc);
559 retval = tty_ldisc_open(tty, new_ldisc);
561 /* Back to the old one or N_TTY if we can't */
562 tty_ldisc_put(new_ldisc);
563 tty_ldisc_restore(tty, old_ldisc);
566 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
567 down_read(&tty->termios_rwsem);
568 tty->ops->set_ldisc(tty);
569 up_read(&tty->termios_rwsem);
572 /* At this point we hold a reference to the new ldisc and a
573 reference to the old ldisc, or we hold two references to
574 the old ldisc (if it was restored as part of error cleanup
575 above). In either case, releasing a single reference from
576 the old ldisc is correct. */
577 new_ldisc = old_ldisc;
579 tty_ldisc_unlock(tty);
581 /* Restart the work queue in case no characters kick it off. Safe if
583 tty_buffer_restart_work(tty->port);
585 tty_ldisc_put(new_ldisc); /* drop the extra reference */
591 * tty_reset_termios - reset terminal state
594 * Restore a terminal to the driver default state.
597 static void tty_reset_termios(struct tty_struct *tty)
599 down_write(&tty->termios_rwsem);
600 tty->termios = tty->driver->init_termios;
601 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
602 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
603 up_write(&tty->termios_rwsem);
608 * tty_ldisc_reinit - reinitialise the tty ldisc
609 * @tty: tty to reinit
610 * @ldisc: line discipline to reinitialize
612 * Switch the tty to a line discipline and leave the ldisc
616 static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
618 struct tty_ldisc *ld = tty_ldisc_get(tty, ldisc);
623 tty_ldisc_close(tty, tty->ldisc);
624 tty_ldisc_put(tty->ldisc);
626 * Switch the line discipline back
629 tty_set_termios_ldisc(tty, ldisc);
635 * tty_ldisc_hangup - hangup ldisc reset
636 * @tty: tty being hung up
638 * Some tty devices reset their termios when they receive a hangup
639 * event. In that situation we must also switch back to N_TTY properly
640 * before we reset the termios data.
642 * Locking: We can take the ldisc mutex as the rest of the code is
643 * careful to allow for this.
645 * In the pty pair case this occurs in the close() path of the
646 * tty itself so we must be careful about locking rules.
649 void tty_ldisc_hangup(struct tty_struct *tty)
651 struct tty_ldisc *ld;
652 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
655 tty_ldisc_debug(tty, "%p: closing\n", tty->ldisc);
657 ld = tty_ldisc_ref(tty);
659 if (ld->ops->flush_buffer)
660 ld->ops->flush_buffer(tty);
661 tty_driver_flush_buffer(tty);
662 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
663 ld->ops->write_wakeup)
664 ld->ops->write_wakeup(tty);
666 ld->ops->hangup(tty);
670 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
671 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
674 * Shutdown the current line discipline, and reset it to
677 * Avoid racing set_ldisc or tty_ldisc_release
679 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
683 /* At this point we have a halted ldisc; we want to close it and
684 reopen a new ldisc. We could defer the reopen to the next
685 open but it means auditing a lot of other paths so this is
689 if (!tty_ldisc_reinit(tty, tty->termios.c_line))
690 err = tty_ldisc_open(tty, tty->ldisc);
694 /* If the re-open fails or we reset then go to N_TTY. The
695 N_TTY open cannot fail */
697 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
698 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
701 tty_ldisc_unlock(tty);
703 tty_reset_termios(tty);
705 tty_ldisc_debug(tty, "%p: re-opened\n", tty->ldisc);
709 * tty_ldisc_setup - open line discipline
710 * @tty: tty being shut down
711 * @o_tty: pair tty for pty/tty pairs
713 * Called during the initial open of a tty/pty pair in order to set up the
714 * line disciplines and bind them to the tty. This has no locking issues
715 * as the device isn't yet active.
718 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
720 struct tty_ldisc *ld = tty->ldisc;
723 retval = tty_ldisc_open(tty, ld);
728 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
730 tty_ldisc_close(tty, ld);
737 static void tty_ldisc_kill(struct tty_struct *tty)
740 * Now kill off the ldisc
742 tty_ldisc_close(tty, tty->ldisc);
743 tty_ldisc_put(tty->ldisc);
744 /* Force an oops if we mess this up */
747 /* Ensure the next open requests the N_TTY ldisc */
748 tty_set_termios_ldisc(tty, N_TTY);
752 * tty_ldisc_release - release line discipline
753 * @tty: tty being shut down (or one end of pty pair)
755 * Called during the final close of a tty or a pty pair in order to shut
756 * down the line discpline layer. On exit, each ldisc assigned is N_TTY and
757 * each ldisc has not been opened.
760 void tty_ldisc_release(struct tty_struct *tty)
762 struct tty_struct *o_tty = tty->link;
765 * Shutdown this line discipline. As this is the final close,
766 * it does not race with the set_ldisc code path.
769 tty_ldisc_lock_pair(tty, o_tty);
772 tty_ldisc_kill(o_tty);
773 tty_ldisc_unlock_pair(tty, o_tty);
775 /* And the memory resources remaining (buffers, termios) will be
776 disposed of when the kref hits zero */
778 tty_ldisc_debug(tty, "released\n");
782 * tty_ldisc_init - ldisc setup for new tty
783 * @tty: tty being allocated
785 * Set up the line discipline objects for a newly allocated tty. Note that
786 * the tty structure is not completely set up when this call is made.
789 void tty_ldisc_init(struct tty_struct *tty)
791 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
793 panic("n_tty: init_tty");
798 * tty_ldisc_deinit - ldisc cleanup for new tty
799 * @tty: tty that was allocated recently
801 * The tty structure must not becompletely set up (tty_ldisc_setup) when
804 void tty_ldisc_deinit(struct tty_struct *tty)
807 tty_ldisc_put(tty->ldisc);
811 void tty_ldisc_begin(void)
813 /* Setup the default TTY line discipline. */
814 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);