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1// SPDX-License-Identifier: GPL-2.0
2#include <linux/types.h>
3#include <linux/errno.h>
4#include <linux/kmod.h>
5#include <linux/sched.h>
6#include <linux/interrupt.h>
7#include <linux/tty.h>
8#include <linux/tty_driver.h>
9#include <linux/file.h>
10#include <linux/mm.h>
11#include <linux/string.h>
12#include <linux/slab.h>
13#include <linux/poll.h>
14#include <linux/proc_fs.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>
22
23#undef LDISC_DEBUG_HANGUP
24
25#ifdef LDISC_DEBUG_HANGUP
26#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
27#else
28#define tty_ldisc_debug(tty, f, args...)
29#endif
30
31/* lockdep nested classes for tty->ldisc_sem */
32enum {
33 LDISC_SEM_NORMAL,
34 LDISC_SEM_OTHER,
35};
36
37
38/*
39 * This guards the refcounted line discipline lists. The lock
40 * must be taken with irqs off because there are hangup path
41 * callers who will do ldisc lookups and cannot sleep.
42 */
43
44static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
45/* Line disc dispatch table */
46static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
47
48/**
49 * tty_register_ldisc - install a line discipline
50 * @disc: ldisc number
51 * @new_ldisc: pointer to the ldisc object
52 *
53 * Installs a new line discipline into the kernel. The discipline
54 * is set up as unreferenced and then made available to the kernel
55 * from this point onwards.
56 *
57 * Locking:
58 * takes tty_ldiscs_lock to guard against ldisc races
59 */
60
61int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
62{
63 unsigned long flags;
64 int ret = 0;
65
66 if (disc < N_TTY || disc >= NR_LDISCS)
67 return -EINVAL;
68
69 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
70 tty_ldiscs[disc] = new_ldisc;
71 new_ldisc->num = disc;
72 new_ldisc->refcount = 0;
73 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
74
75 return ret;
76}
77EXPORT_SYMBOL(tty_register_ldisc);
78
79/**
80 * tty_unregister_ldisc - unload a line discipline
81 * @disc: ldisc number
82 * @new_ldisc: pointer to the ldisc object
83 *
84 * Remove a line discipline from the kernel providing it is not
85 * currently in use.
86 *
87 * Locking:
88 * takes tty_ldiscs_lock to guard against ldisc races
89 */
90
91int tty_unregister_ldisc(int disc)
92{
93 unsigned long flags;
94 int ret = 0;
95
96 if (disc < N_TTY || disc >= NR_LDISCS)
97 return -EINVAL;
98
99 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
100 if (tty_ldiscs[disc]->refcount)
101 ret = -EBUSY;
102 else
103 tty_ldiscs[disc] = NULL;
104 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
105
106 return ret;
107}
108EXPORT_SYMBOL(tty_unregister_ldisc);
109
110static struct tty_ldisc_ops *get_ldops(int disc)
111{
112 unsigned long flags;
113 struct tty_ldisc_ops *ldops, *ret;
114
115 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
116 ret = ERR_PTR(-EINVAL);
117 ldops = tty_ldiscs[disc];
118 if (ldops) {
119 ret = ERR_PTR(-EAGAIN);
120 if (try_module_get(ldops->owner)) {
121 ldops->refcount++;
122 ret = ldops;
123 }
124 }
125 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
126 return ret;
127}
128
129static void put_ldops(struct tty_ldisc_ops *ldops)
130{
131 unsigned long flags;
132
133 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
134 ldops->refcount--;
135 module_put(ldops->owner);
136 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
137}
138
139/**
140 * tty_ldisc_get - take a reference to an ldisc
141 * @disc: ldisc number
142 *
143 * Takes a reference to a line discipline. Deals with refcounts and
144 * module locking counts.
145 *
146 * Returns: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
147 * if the discipline is not registered
148 * -EAGAIN if request_module() failed to load or register the
149 * the discipline
150 * -ENOMEM if allocation failure
151 *
152 * Otherwise, returns a pointer to the discipline and bumps the
153 * ref count
154 *
155 * Locking:
156 * takes tty_ldiscs_lock to guard against ldisc races
157 */
158
159#if defined(CONFIG_LDISC_AUTOLOAD)
160 #define INITIAL_AUTOLOAD_STATE 1
161#else
162 #define INITIAL_AUTOLOAD_STATE 0
163#endif
164static int tty_ldisc_autoload = INITIAL_AUTOLOAD_STATE;
165
166static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
167{
168 struct tty_ldisc *ld;
169 struct tty_ldisc_ops *ldops;
170
171 if (disc < N_TTY || disc >= NR_LDISCS)
172 return ERR_PTR(-EINVAL);
173
174 /*
175 * Get the ldisc ops - we may need to request them to be loaded
176 * dynamically and try again.
177 */
178 ldops = get_ldops(disc);
179 if (IS_ERR(ldops)) {
180 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
181 return ERR_PTR(-EPERM);
182 request_module("tty-ldisc-%d", disc);
183 ldops = get_ldops(disc);
184 if (IS_ERR(ldops))
185 return ERR_CAST(ldops);
186 }
187
188 /*
189 * There is no way to handle allocation failure of only 16 bytes.
190 * Let's simplify error handling and save more memory.
191 */
192 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
193 ld->ops = ldops;
194 ld->tty = tty;
195
196 return ld;
197}
198
199/**
200 * tty_ldisc_put - release the ldisc
201 *
202 * Complement of tty_ldisc_get().
203 */
204static void tty_ldisc_put(struct tty_ldisc *ld)
205{
206 if (WARN_ON_ONCE(!ld))
207 return;
208
209 put_ldops(ld->ops);
210 kfree(ld);
211}
212
213static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
214{
215 return (*pos < NR_LDISCS) ? pos : NULL;
216}
217
218static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
219{
220 (*pos)++;
221 return (*pos < NR_LDISCS) ? pos : NULL;
222}
223
224static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
225{
226}
227
228static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
229{
230 int i = *(loff_t *)v;
231 struct tty_ldisc_ops *ldops;
232
233 ldops = get_ldops(i);
234 if (IS_ERR(ldops))
235 return 0;
236 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
237 put_ldops(ldops);
238 return 0;
239}
240
241const 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,
246};
247
248/**
249 * tty_ldisc_ref_wait - wait for the tty ldisc
250 * @tty: tty device
251 *
252 * Dereference the line discipline for the terminal and take a
253 * reference to it. If the line discipline is in flux then
254 * wait patiently until it changes.
255 *
256 * Returns: NULL if the tty has been hungup and not re-opened with
257 * a new file descriptor, otherwise valid ldisc reference
258 *
259 * Note: Must not be called from an IRQ/timer context. The caller
260 * must also be careful not to hold other locks that will deadlock
261 * against a discipline change, such as an existing ldisc reference
262 * (which we check for)
263 *
264 * Note: a file_operations routine (read/poll/write) should use this
265 * function to wait for any ldisc lifetime events to finish.
266 */
267
268struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
269{
270 struct tty_ldisc *ld;
271
272 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
273 ld = tty->ldisc;
274 if (!ld)
275 ldsem_up_read(&tty->ldisc_sem);
276 return ld;
277}
278EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
279
280/**
281 * tty_ldisc_ref - get the tty ldisc
282 * @tty: tty device
283 *
284 * Dereference the line discipline for the terminal and take a
285 * reference to it. If the line discipline is in flux then
286 * return NULL. Can be called from IRQ and timer functions.
287 */
288
289struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
290{
291 struct tty_ldisc *ld = NULL;
292
293 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
294 ld = tty->ldisc;
295 if (!ld)
296 ldsem_up_read(&tty->ldisc_sem);
297 }
298 return ld;
299}
300EXPORT_SYMBOL_GPL(tty_ldisc_ref);
301
302/**
303 * tty_ldisc_deref - free a tty ldisc reference
304 * @ld: reference to free up
305 *
306 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
307 * be called in IRQ context.
308 */
309
310void tty_ldisc_deref(struct tty_ldisc *ld)
311{
312 ldsem_up_read(&ld->tty->ldisc_sem);
313}
314EXPORT_SYMBOL_GPL(tty_ldisc_deref);
315
316
317static inline int
318__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
319{
320 return ldsem_down_write(&tty->ldisc_sem, timeout);
321}
322
323static inline int
324__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
325{
326 return ldsem_down_write_nested(&tty->ldisc_sem,
327 LDISC_SEM_OTHER, timeout);
328}
329
330static inline void __tty_ldisc_unlock(struct tty_struct *tty)
331{
332 ldsem_up_write(&tty->ldisc_sem);
333}
334
335int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
336{
337 int ret;
338
339 /* Kindly asking blocked readers to release the read side */
340 set_bit(TTY_LDISC_CHANGING, &tty->flags);
341 wake_up_interruptible_all(&tty->read_wait);
342 wake_up_interruptible_all(&tty->write_wait);
343
344 ret = __tty_ldisc_lock(tty, timeout);
345 if (!ret)
346 return -EBUSY;
347 set_bit(TTY_LDISC_HALTED, &tty->flags);
348 return 0;
349}
350
351void tty_ldisc_unlock(struct tty_struct *tty)
352{
353 clear_bit(TTY_LDISC_HALTED, &tty->flags);
354 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
355 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
356 __tty_ldisc_unlock(tty);
357}
358
359static int
360tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
361 unsigned long timeout)
362{
363 int ret;
364
365 if (tty < tty2) {
366 ret = __tty_ldisc_lock(tty, timeout);
367 if (ret) {
368 ret = __tty_ldisc_lock_nested(tty2, timeout);
369 if (!ret)
370 __tty_ldisc_unlock(tty);
371 }
372 } else {
373 /* if this is possible, it has lots of implications */
374 WARN_ON_ONCE(tty == tty2);
375 if (tty2 && tty != tty2) {
376 ret = __tty_ldisc_lock(tty2, timeout);
377 if (ret) {
378 ret = __tty_ldisc_lock_nested(tty, timeout);
379 if (!ret)
380 __tty_ldisc_unlock(tty2);
381 }
382 } else
383 ret = __tty_ldisc_lock(tty, timeout);
384 }
385
386 if (!ret)
387 return -EBUSY;
388
389 set_bit(TTY_LDISC_HALTED, &tty->flags);
390 if (tty2)
391 set_bit(TTY_LDISC_HALTED, &tty2->flags);
392 return 0;
393}
394
395static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
396{
397 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
398}
399
400static void tty_ldisc_unlock_pair(struct tty_struct *tty,
401 struct tty_struct *tty2)
402{
403 __tty_ldisc_unlock(tty);
404 if (tty2)
405 __tty_ldisc_unlock(tty2);
406}
407
408/**
409 * tty_ldisc_flush - flush line discipline queue
410 * @tty: tty
411 *
412 * Flush the line discipline queue (if any) and the tty flip buffers
413 * for this tty.
414 */
415
416void tty_ldisc_flush(struct tty_struct *tty)
417{
418 struct tty_ldisc *ld = tty_ldisc_ref(tty);
419
420 tty_buffer_flush(tty, ld);
421 if (ld)
422 tty_ldisc_deref(ld);
423}
424EXPORT_SYMBOL_GPL(tty_ldisc_flush);
425
426/**
427 * tty_set_termios_ldisc - set ldisc field
428 * @tty: tty structure
429 * @disc: line discipline number
430 *
431 * This is probably overkill for real world processors but
432 * they are not on hot paths so a little discipline won't do
433 * any harm.
434 *
435 * The line discipline-related tty_struct fields are reset to
436 * prevent the ldisc driver from re-using stale information for
437 * the new ldisc instance.
438 *
439 * Locking: takes termios_rwsem
440 */
441
442static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
443{
444 down_write(&tty->termios_rwsem);
445 tty->termios.c_line = disc;
446 up_write(&tty->termios_rwsem);
447
448 tty->disc_data = NULL;
449 tty->receive_room = 0;
450}
451
452/**
453 * tty_ldisc_open - open a line discipline
454 * @tty: tty we are opening the ldisc on
455 * @ld: discipline to open
456 *
457 * A helper opening method. Also a convenient debugging and check
458 * point.
459 *
460 * Locking: always called with BTM already held.
461 */
462
463static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
464{
465 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
466 if (ld->ops->open) {
467 int ret;
468 /* BTM here locks versus a hangup event */
469 ret = ld->ops->open(tty);
470 if (ret)
471 clear_bit(TTY_LDISC_OPEN, &tty->flags);
472
473 tty_ldisc_debug(tty, "%p: opened\n", ld);
474 return ret;
475 }
476 return 0;
477}
478
479/**
480 * tty_ldisc_close - close a line discipline
481 * @tty: tty we are opening the ldisc on
482 * @ld: discipline to close
483 *
484 * A helper close method. Also a convenient debugging and check
485 * point.
486 */
487
488static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
489{
490 lockdep_assert_held_write(&tty->ldisc_sem);
491 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
492 clear_bit(TTY_LDISC_OPEN, &tty->flags);
493 if (ld->ops->close)
494 ld->ops->close(tty);
495 tty_ldisc_debug(tty, "%p: closed\n", ld);
496}
497
498/**
499 * tty_ldisc_failto - helper for ldisc failback
500 * @tty: tty to open the ldisc on
501 * @ld: ldisc we are trying to fail back to
502 *
503 * Helper to try and recover a tty when switching back to the old
504 * ldisc fails and we need something attached.
505 */
506
507static int tty_ldisc_failto(struct tty_struct *tty, int ld)
508{
509 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
510 int r;
511
512 lockdep_assert_held_write(&tty->ldisc_sem);
513 if (IS_ERR(disc))
514 return PTR_ERR(disc);
515 tty->ldisc = disc;
516 tty_set_termios_ldisc(tty, ld);
517 if ((r = tty_ldisc_open(tty, disc)) < 0)
518 tty_ldisc_put(disc);
519 return r;
520}
521
522/**
523 * tty_ldisc_restore - helper for tty ldisc change
524 * @tty: tty to recover
525 * @old: previous ldisc
526 *
527 * Restore the previous line discipline or N_TTY when a line discipline
528 * change fails due to an open error
529 */
530
531static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
532{
533 /* There is an outstanding reference here so this is safe */
534 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
535 const char *name = tty_name(tty);
536
537 pr_warn("Falling back ldisc for %s.\n", name);
538 /* The traditional behaviour is to fall back to N_TTY, we
539 want to avoid falling back to N_NULL unless we have no
540 choice to avoid the risk of breaking anything */
541 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
542 tty_ldisc_failto(tty, N_NULL) < 0)
543 panic("Couldn't open N_NULL ldisc for %s.", name);
544 }
545}
546
547/**
548 * tty_set_ldisc - set line discipline
549 * @tty: the terminal to set
550 * @ldisc: the line discipline
551 *
552 * Set the discipline of a tty line. Must be called from a process
553 * context. The ldisc change logic has to protect itself against any
554 * overlapping ldisc change (including on the other end of pty pairs),
555 * the close of one side of a tty/pty pair, and eventually hangup.
556 */
557
558int tty_set_ldisc(struct tty_struct *tty, int disc)
559{
560 int retval;
561 struct tty_ldisc *old_ldisc, *new_ldisc;
562
563 new_ldisc = tty_ldisc_get(tty, disc);
564 if (IS_ERR(new_ldisc))
565 return PTR_ERR(new_ldisc);
566
567 tty_lock(tty);
568 retval = tty_ldisc_lock(tty, 5 * HZ);
569 if (retval)
570 goto err;
571
572 if (!tty->ldisc) {
573 retval = -EIO;
574 goto out;
575 }
576
577 /* Check the no-op case */
578 if (tty->ldisc->ops->num == disc)
579 goto out;
580
581 if (test_bit(TTY_HUPPED, &tty->flags)) {
582 /* We were raced by hangup */
583 retval = -EIO;
584 goto out;
585 }
586
587 old_ldisc = tty->ldisc;
588
589 /* Shutdown the old discipline. */
590 tty_ldisc_close(tty, old_ldisc);
591
592 /* Now set up the new line discipline. */
593 tty->ldisc = new_ldisc;
594 tty_set_termios_ldisc(tty, disc);
595
596 retval = tty_ldisc_open(tty, new_ldisc);
597 if (retval < 0) {
598 /* Back to the old one or N_TTY if we can't */
599 tty_ldisc_put(new_ldisc);
600 tty_ldisc_restore(tty, old_ldisc);
601 }
602
603 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
604 down_read(&tty->termios_rwsem);
605 tty->ops->set_ldisc(tty);
606 up_read(&tty->termios_rwsem);
607 }
608
609 /* At this point we hold a reference to the new ldisc and a
610 reference to the old ldisc, or we hold two references to
611 the old ldisc (if it was restored as part of error cleanup
612 above). In either case, releasing a single reference from
613 the old ldisc is correct. */
614 new_ldisc = old_ldisc;
615out:
616 tty_ldisc_unlock(tty);
617
618 /* Restart the work queue in case no characters kick it off. Safe if
619 already running */
620 tty_buffer_restart_work(tty->port);
621err:
622 tty_ldisc_put(new_ldisc); /* drop the extra reference */
623 tty_unlock(tty);
624 return retval;
625}
626EXPORT_SYMBOL_GPL(tty_set_ldisc);
627
628/**
629 * tty_ldisc_kill - teardown ldisc
630 * @tty: tty being released
631 *
632 * Perform final close of the ldisc and reset tty->ldisc
633 */
634static void tty_ldisc_kill(struct tty_struct *tty)
635{
636 lockdep_assert_held_write(&tty->ldisc_sem);
637 if (!tty->ldisc)
638 return;
639 /*
640 * Now kill off the ldisc
641 */
642 tty_ldisc_close(tty, tty->ldisc);
643 tty_ldisc_put(tty->ldisc);
644 /* Force an oops if we mess this up */
645 tty->ldisc = NULL;
646}
647
648/**
649 * tty_reset_termios - reset terminal state
650 * @tty: tty to reset
651 *
652 * Restore a terminal to the driver default state.
653 */
654
655static void tty_reset_termios(struct tty_struct *tty)
656{
657 down_write(&tty->termios_rwsem);
658 tty->termios = tty->driver->init_termios;
659 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
660 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
661 up_write(&tty->termios_rwsem);
662}
663
664
665/**
666 * tty_ldisc_reinit - reinitialise the tty ldisc
667 * @tty: tty to reinit
668 * @disc: line discipline to reinitialize
669 *
670 * Completely reinitialize the line discipline state, by closing the
671 * current instance, if there is one, and opening a new instance. If
672 * an error occurs opening the new non-N_TTY instance, the instance
673 * is dropped and tty->ldisc reset to NULL. The caller can then retry
674 * with N_TTY instead.
675 *
676 * Returns 0 if successful, otherwise error code < 0
677 */
678
679int tty_ldisc_reinit(struct tty_struct *tty, int disc)
680{
681 struct tty_ldisc *ld;
682 int retval;
683
684 lockdep_assert_held_write(&tty->ldisc_sem);
685 ld = tty_ldisc_get(tty, disc);
686 if (IS_ERR(ld)) {
687 BUG_ON(disc == N_TTY);
688 return PTR_ERR(ld);
689 }
690
691 if (tty->ldisc) {
692 tty_ldisc_close(tty, tty->ldisc);
693 tty_ldisc_put(tty->ldisc);
694 }
695
696 /* switch the line discipline */
697 tty->ldisc = ld;
698 tty_set_termios_ldisc(tty, disc);
699 retval = tty_ldisc_open(tty, tty->ldisc);
700 if (retval) {
701 tty_ldisc_put(tty->ldisc);
702 tty->ldisc = NULL;
703 }
704 return retval;
705}
706
707/**
708 * tty_ldisc_hangup - hangup ldisc reset
709 * @tty: tty being hung up
710 *
711 * Some tty devices reset their termios when they receive a hangup
712 * event. In that situation we must also switch back to N_TTY properly
713 * before we reset the termios data.
714 *
715 * Locking: We can take the ldisc mutex as the rest of the code is
716 * careful to allow for this.
717 *
718 * In the pty pair case this occurs in the close() path of the
719 * tty itself so we must be careful about locking rules.
720 */
721
722void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
723{
724 struct tty_ldisc *ld;
725
726 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
727
728 ld = tty_ldisc_ref(tty);
729 if (ld != NULL) {
730 if (ld->ops->flush_buffer)
731 ld->ops->flush_buffer(tty);
732 tty_driver_flush_buffer(tty);
733 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
734 ld->ops->write_wakeup)
735 ld->ops->write_wakeup(tty);
736 if (ld->ops->hangup)
737 ld->ops->hangup(tty);
738 tty_ldisc_deref(ld);
739 }
740
741 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
742 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
743
744 /*
745 * Shutdown the current line discipline, and reset it to
746 * N_TTY if need be.
747 *
748 * Avoid racing set_ldisc or tty_ldisc_release
749 */
750 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
751
752 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
753 tty_reset_termios(tty);
754
755 if (tty->ldisc) {
756 if (reinit) {
757 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
758 tty_ldisc_reinit(tty, N_TTY) < 0)
759 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
760 } else
761 tty_ldisc_kill(tty);
762 }
763 tty_ldisc_unlock(tty);
764}
765
766/**
767 * tty_ldisc_setup - open line discipline
768 * @tty: tty being shut down
769 * @o_tty: pair tty for pty/tty pairs
770 *
771 * Called during the initial open of a tty/pty pair in order to set up the
772 * line disciplines and bind them to the tty. This has no locking issues
773 * as the device isn't yet active.
774 */
775
776int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
777{
778 int retval = tty_ldisc_open(tty, tty->ldisc);
779 if (retval)
780 return retval;
781
782 if (o_tty) {
783 /*
784 * Called without o_tty->ldisc_sem held, as o_tty has been
785 * just allocated and no one has a reference to it.
786 */
787 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
788 if (retval) {
789 tty_ldisc_close(tty, tty->ldisc);
790 return retval;
791 }
792 }
793 return 0;
794}
795
796/**
797 * tty_ldisc_release - release line discipline
798 * @tty: tty being shut down (or one end of pty pair)
799 *
800 * Called during the final close of a tty or a pty pair in order to shut
801 * down the line discpline layer. On exit, each tty's ldisc is NULL.
802 */
803
804void tty_ldisc_release(struct tty_struct *tty)
805{
806 struct tty_struct *o_tty = tty->link;
807
808 /*
809 * Shutdown this line discipline. As this is the final close,
810 * it does not race with the set_ldisc code path.
811 */
812
813 tty_ldisc_lock_pair(tty, o_tty);
814 tty_ldisc_kill(tty);
815 if (o_tty)
816 tty_ldisc_kill(o_tty);
817 tty_ldisc_unlock_pair(tty, o_tty);
818
819 /* And the memory resources remaining (buffers, termios) will be
820 disposed of when the kref hits zero */
821
822 tty_ldisc_debug(tty, "released\n");
823}
824EXPORT_SYMBOL_GPL(tty_ldisc_release);
825
826/**
827 * tty_ldisc_init - ldisc setup for new tty
828 * @tty: tty being allocated
829 *
830 * Set up the line discipline objects for a newly allocated tty. Note that
831 * the tty structure is not completely set up when this call is made.
832 */
833
834int tty_ldisc_init(struct tty_struct *tty)
835{
836 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
837 if (IS_ERR(ld))
838 return PTR_ERR(ld);
839 tty->ldisc = ld;
840 return 0;
841}
842
843/**
844 * tty_ldisc_deinit - ldisc cleanup for new tty
845 * @tty: tty that was allocated recently
846 *
847 * The tty structure must not becompletely set up (tty_ldisc_setup) when
848 * this call is made.
849 */
850void tty_ldisc_deinit(struct tty_struct *tty)
851{
852 /* no ldisc_sem, tty is being destroyed */
853 if (tty->ldisc)
854 tty_ldisc_put(tty->ldisc);
855 tty->ldisc = NULL;
856}
857
858static struct ctl_table tty_table[] = {
859 {
860 .procname = "ldisc_autoload",
861 .data = &tty_ldisc_autoload,
862 .maxlen = sizeof(tty_ldisc_autoload),
863 .mode = 0644,
864 .proc_handler = proc_dointvec,
865 .extra1 = SYSCTL_ZERO,
866 .extra2 = SYSCTL_ONE,
867 },
868 { }
869};
870
871static struct ctl_table tty_dir_table[] = {
872 {
873 .procname = "tty",
874 .mode = 0555,
875 .child = tty_table,
876 },
877 { }
878};
879
880static struct ctl_table tty_root_table[] = {
881 {
882 .procname = "dev",
883 .mode = 0555,
884 .child = tty_dir_table,
885 },
886 { }
887};
888
889void tty_sysctl_init(void)
890{
891 register_sysctl_table(tty_root_table);
892}
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>
6#include <linux/tty.h>
7#include <linux/tty_driver.h>
8#include <linux/file.h>
9#include <linux/mm.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>
21
22#undef LDISC_DEBUG_HANGUP
23
24#ifdef LDISC_DEBUG_HANGUP
25#define tty_ldisc_debug(tty, f, args...) ({ \
26 char __b[64]; \
27 printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
28})
29#else
30#define tty_ldisc_debug(tty, f, args...)
31#endif
32
33/* lockdep nested classes for tty->ldisc_sem */
34enum {
35 LDISC_SEM_NORMAL,
36 LDISC_SEM_OTHER,
37};
38
39
40/*
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.
44 */
45
46static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
47/* Line disc dispatch table */
48static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
49
50/**
51 * tty_register_ldisc - install a line discipline
52 * @disc: ldisc number
53 * @new_ldisc: pointer to the ldisc object
54 *
55 * Installs a new line discipline into the kernel. The discipline
56 * is set up as unreferenced and then made available to the kernel
57 * from this point onwards.
58 *
59 * Locking:
60 * takes tty_ldiscs_lock to guard against ldisc races
61 */
62
63int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
64{
65 unsigned long flags;
66 int ret = 0;
67
68 if (disc < N_TTY || disc >= NR_LDISCS)
69 return -EINVAL;
70
71 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
72 tty_ldiscs[disc] = new_ldisc;
73 new_ldisc->num = disc;
74 new_ldisc->refcount = 0;
75 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
76
77 return ret;
78}
79EXPORT_SYMBOL(tty_register_ldisc);
80
81/**
82 * tty_unregister_ldisc - unload a line discipline
83 * @disc: ldisc number
84 * @new_ldisc: pointer to the ldisc object
85 *
86 * Remove a line discipline from the kernel providing it is not
87 * currently in use.
88 *
89 * Locking:
90 * takes tty_ldiscs_lock to guard against ldisc races
91 */
92
93int tty_unregister_ldisc(int disc)
94{
95 unsigned long flags;
96 int ret = 0;
97
98 if (disc < N_TTY || disc >= NR_LDISCS)
99 return -EINVAL;
100
101 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
102 if (tty_ldiscs[disc]->refcount)
103 ret = -EBUSY;
104 else
105 tty_ldiscs[disc] = NULL;
106 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107
108 return ret;
109}
110EXPORT_SYMBOL(tty_unregister_ldisc);
111
112static struct tty_ldisc_ops *get_ldops(int disc)
113{
114 unsigned long flags;
115 struct tty_ldisc_ops *ldops, *ret;
116
117 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
118 ret = ERR_PTR(-EINVAL);
119 ldops = tty_ldiscs[disc];
120 if (ldops) {
121 ret = ERR_PTR(-EAGAIN);
122 if (try_module_get(ldops->owner)) {
123 ldops->refcount++;
124 ret = ldops;
125 }
126 }
127 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
128 return ret;
129}
130
131static void put_ldops(struct tty_ldisc_ops *ldops)
132{
133 unsigned long flags;
134
135 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
136 ldops->refcount--;
137 module_put(ldops->owner);
138 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
139}
140
141/**
142 * tty_ldisc_get - take a reference to an ldisc
143 * @disc: ldisc number
144 *
145 * Takes a reference to a line discipline. Deals with refcounts and
146 * module locking counts. Returns NULL if the discipline is not available.
147 * Returns a pointer to the discipline and bumps the ref count if it is
148 * available
149 *
150 * Locking:
151 * takes tty_ldiscs_lock to guard against ldisc races
152 */
153
154static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
155{
156 struct tty_ldisc *ld;
157 struct tty_ldisc_ops *ldops;
158
159 if (disc < N_TTY || disc >= NR_LDISCS)
160 return ERR_PTR(-EINVAL);
161
162 /*
163 * Get the ldisc ops - we may need to request them to be loaded
164 * dynamically and try again.
165 */
166 ldops = get_ldops(disc);
167 if (IS_ERR(ldops)) {
168 request_module("tty-ldisc-%d", disc);
169 ldops = get_ldops(disc);
170 if (IS_ERR(ldops))
171 return ERR_CAST(ldops);
172 }
173
174 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
175 if (ld == NULL) {
176 put_ldops(ldops);
177 return ERR_PTR(-ENOMEM);
178 }
179
180 ld->ops = ldops;
181 ld->tty = tty;
182
183 return ld;
184}
185
186/**
187 * tty_ldisc_put - release the ldisc
188 *
189 * Complement of tty_ldisc_get().
190 */
191static inline void tty_ldisc_put(struct tty_ldisc *ld)
192{
193 if (WARN_ON_ONCE(!ld))
194 return;
195
196 put_ldops(ld->ops);
197 kfree(ld);
198}
199
200static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
201{
202 return (*pos < NR_LDISCS) ? pos : NULL;
203}
204
205static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
206{
207 (*pos)++;
208 return (*pos < NR_LDISCS) ? pos : NULL;
209}
210
211static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
212{
213}
214
215static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
216{
217 int i = *(loff_t *)v;
218 struct tty_ldisc_ops *ldops;
219
220 ldops = get_ldops(i);
221 if (IS_ERR(ldops))
222 return 0;
223 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
224 put_ldops(ldops);
225 return 0;
226}
227
228static const struct seq_operations tty_ldiscs_seq_ops = {
229 .start = tty_ldiscs_seq_start,
230 .next = tty_ldiscs_seq_next,
231 .stop = tty_ldiscs_seq_stop,
232 .show = tty_ldiscs_seq_show,
233};
234
235static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
236{
237 return seq_open(file, &tty_ldiscs_seq_ops);
238}
239
240const struct file_operations tty_ldiscs_proc_fops = {
241 .owner = THIS_MODULE,
242 .open = proc_tty_ldiscs_open,
243 .read = seq_read,
244 .llseek = seq_lseek,
245 .release = seq_release,
246};
247
248/**
249 * tty_ldisc_ref_wait - wait for the tty ldisc
250 * @tty: tty device
251 *
252 * Dereference the line discipline for the terminal and take a
253 * reference to it. If the line discipline is in flux then
254 * wait patiently until it changes.
255 *
256 * Note: Must not be called from an IRQ/timer context. The caller
257 * must also be careful not to hold other locks that will deadlock
258 * against a discipline change, such as an existing ldisc reference
259 * (which we check for)
260 *
261 * Note: only callable from a file_operations routine (which
262 * guarantees tty->ldisc != NULL when the lock is acquired).
263 */
264
265struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
266{
267 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
268 WARN_ON(!tty->ldisc);
269 return tty->ldisc;
270}
271EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
272
273/**
274 * tty_ldisc_ref - get the tty ldisc
275 * @tty: tty device
276 *
277 * Dereference the line discipline for the terminal and take a
278 * reference to it. If the line discipline is in flux then
279 * return NULL. Can be called from IRQ and timer functions.
280 */
281
282struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
283{
284 struct tty_ldisc *ld = NULL;
285
286 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
287 ld = tty->ldisc;
288 if (!ld)
289 ldsem_up_read(&tty->ldisc_sem);
290 }
291 return ld;
292}
293EXPORT_SYMBOL_GPL(tty_ldisc_ref);
294
295/**
296 * tty_ldisc_deref - free a tty ldisc reference
297 * @ld: reference to free up
298 *
299 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
300 * be called in IRQ context.
301 */
302
303void tty_ldisc_deref(struct tty_ldisc *ld)
304{
305 ldsem_up_read(&ld->tty->ldisc_sem);
306}
307EXPORT_SYMBOL_GPL(tty_ldisc_deref);
308
309
310static inline int __lockfunc
311tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
312{
313 return ldsem_down_write(&tty->ldisc_sem, timeout);
314}
315
316static inline int __lockfunc
317tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
318{
319 return ldsem_down_write_nested(&tty->ldisc_sem,
320 LDISC_SEM_OTHER, timeout);
321}
322
323static inline void tty_ldisc_unlock(struct tty_struct *tty)
324{
325 return ldsem_up_write(&tty->ldisc_sem);
326}
327
328static int __lockfunc
329tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
330 unsigned long timeout)
331{
332 int ret;
333
334 if (tty < tty2) {
335 ret = tty_ldisc_lock(tty, timeout);
336 if (ret) {
337 ret = tty_ldisc_lock_nested(tty2, timeout);
338 if (!ret)
339 tty_ldisc_unlock(tty);
340 }
341 } else {
342 /* if this is possible, it has lots of implications */
343 WARN_ON_ONCE(tty == tty2);
344 if (tty2 && tty != tty2) {
345 ret = tty_ldisc_lock(tty2, timeout);
346 if (ret) {
347 ret = tty_ldisc_lock_nested(tty, timeout);
348 if (!ret)
349 tty_ldisc_unlock(tty2);
350 }
351 } else
352 ret = tty_ldisc_lock(tty, timeout);
353 }
354
355 if (!ret)
356 return -EBUSY;
357
358 set_bit(TTY_LDISC_HALTED, &tty->flags);
359 if (tty2)
360 set_bit(TTY_LDISC_HALTED, &tty2->flags);
361 return 0;
362}
363
364static void __lockfunc
365tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
366{
367 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
368}
369
370static void __lockfunc tty_ldisc_unlock_pair(struct tty_struct *tty,
371 struct tty_struct *tty2)
372{
373 tty_ldisc_unlock(tty);
374 if (tty2)
375 tty_ldisc_unlock(tty2);
376}
377
378static void __lockfunc tty_ldisc_enable_pair(struct tty_struct *tty,
379 struct tty_struct *tty2)
380{
381 clear_bit(TTY_LDISC_HALTED, &tty->flags);
382 if (tty2)
383 clear_bit(TTY_LDISC_HALTED, &tty2->flags);
384
385 tty_ldisc_unlock_pair(tty, tty2);
386}
387
388/**
389 * tty_ldisc_flush - flush line discipline queue
390 * @tty: tty
391 *
392 * Flush the line discipline queue (if any) for this tty. If there
393 * is no line discipline active this is a no-op.
394 */
395
396void tty_ldisc_flush(struct tty_struct *tty)
397{
398 struct tty_ldisc *ld = tty_ldisc_ref(tty);
399 if (ld) {
400 if (ld->ops->flush_buffer)
401 ld->ops->flush_buffer(tty);
402 tty_ldisc_deref(ld);
403 }
404 tty_buffer_flush(tty);
405}
406EXPORT_SYMBOL_GPL(tty_ldisc_flush);
407
408/**
409 * tty_set_termios_ldisc - set ldisc field
410 * @tty: tty structure
411 * @num: line discipline number
412 *
413 * This is probably overkill for real world processors but
414 * they are not on hot paths so a little discipline won't do
415 * any harm.
416 *
417 * Locking: takes termios_rwsem
418 */
419
420static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
421{
422 down_write(&tty->termios_rwsem);
423 tty->termios.c_line = num;
424 up_write(&tty->termios_rwsem);
425}
426
427/**
428 * tty_ldisc_open - open a line discipline
429 * @tty: tty we are opening the ldisc on
430 * @ld: discipline to open
431 *
432 * A helper opening method. Also a convenient debugging and check
433 * point.
434 *
435 * Locking: always called with BTM already held.
436 */
437
438static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
439{
440 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
441 if (ld->ops->open) {
442 int ret;
443 /* BTM here locks versus a hangup event */
444 ret = ld->ops->open(tty);
445 if (ret)
446 clear_bit(TTY_LDISC_OPEN, &tty->flags);
447 return ret;
448 }
449 return 0;
450}
451
452/**
453 * tty_ldisc_close - close a line discipline
454 * @tty: tty we are opening the ldisc on
455 * @ld: discipline to close
456 *
457 * A helper close method. Also a convenient debugging and check
458 * point.
459 */
460
461static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
462{
463 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
464 clear_bit(TTY_LDISC_OPEN, &tty->flags);
465 if (ld->ops->close)
466 ld->ops->close(tty);
467}
468
469/**
470 * tty_ldisc_restore - helper for tty ldisc change
471 * @tty: tty to recover
472 * @old: previous ldisc
473 *
474 * Restore the previous line discipline or N_TTY when a line discipline
475 * change fails due to an open error
476 */
477
478static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
479{
480 char buf[64];
481 struct tty_ldisc *new_ldisc;
482 int r;
483
484 /* There is an outstanding reference here so this is safe */
485 old = tty_ldisc_get(tty, old->ops->num);
486 WARN_ON(IS_ERR(old));
487 tty->ldisc = old;
488 tty_set_termios_ldisc(tty, old->ops->num);
489 if (tty_ldisc_open(tty, old) < 0) {
490 tty_ldisc_put(old);
491 /* This driver is always present */
492 new_ldisc = tty_ldisc_get(tty, N_TTY);
493 if (IS_ERR(new_ldisc))
494 panic("n_tty: get");
495 tty->ldisc = new_ldisc;
496 tty_set_termios_ldisc(tty, N_TTY);
497 r = tty_ldisc_open(tty, new_ldisc);
498 if (r < 0)
499 panic("Couldn't open N_TTY ldisc for "
500 "%s --- error %d.",
501 tty_name(tty, buf), r);
502 }
503}
504
505/**
506 * tty_set_ldisc - set line discipline
507 * @tty: the terminal to set
508 * @ldisc: the line discipline
509 *
510 * Set the discipline of a tty line. Must be called from a process
511 * context. The ldisc change logic has to protect itself against any
512 * overlapping ldisc change (including on the other end of pty pairs),
513 * the close of one side of a tty/pty pair, and eventually hangup.
514 */
515
516int tty_set_ldisc(struct tty_struct *tty, int ldisc)
517{
518 int retval;
519 struct tty_ldisc *old_ldisc, *new_ldisc;
520 struct tty_struct *o_tty = tty->link;
521
522 new_ldisc = tty_ldisc_get(tty, ldisc);
523 if (IS_ERR(new_ldisc))
524 return PTR_ERR(new_ldisc);
525
526 retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
527 if (retval) {
528 tty_ldisc_put(new_ldisc);
529 return retval;
530 }
531
532 /*
533 * Check the no-op case
534 */
535
536 if (tty->ldisc->ops->num == ldisc) {
537 tty_ldisc_enable_pair(tty, o_tty);
538 tty_ldisc_put(new_ldisc);
539 return 0;
540 }
541
542 old_ldisc = tty->ldisc;
543 tty_lock(tty);
544
545 if (test_bit(TTY_HUPPING, &tty->flags) ||
546 test_bit(TTY_HUPPED, &tty->flags)) {
547 /* We were raced by the hangup method. It will have stomped
548 the ldisc data and closed the ldisc down */
549 tty_ldisc_enable_pair(tty, o_tty);
550 tty_ldisc_put(new_ldisc);
551 tty_unlock(tty);
552 return -EIO;
553 }
554
555 /* Shutdown the old discipline. */
556 tty_ldisc_close(tty, old_ldisc);
557
558 /* Now set up the new line discipline. */
559 tty->ldisc = new_ldisc;
560 tty_set_termios_ldisc(tty, ldisc);
561
562 retval = tty_ldisc_open(tty, new_ldisc);
563 if (retval < 0) {
564 /* Back to the old one or N_TTY if we can't */
565 tty_ldisc_put(new_ldisc);
566 tty_ldisc_restore(tty, old_ldisc);
567 }
568
569 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc)
570 tty->ops->set_ldisc(tty);
571
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
578 tty_ldisc_put(old_ldisc);
579
580 /*
581 * Allow ldisc referencing to occur again
582 */
583 tty_ldisc_enable_pair(tty, o_tty);
584
585 /* Restart the work queue in case no characters kick it off. Safe if
586 already running */
587 schedule_work(&tty->port->buf.work);
588 if (o_tty)
589 schedule_work(&o_tty->port->buf.work);
590
591 tty_unlock(tty);
592 return retval;
593}
594
595/**
596 * tty_reset_termios - reset terminal state
597 * @tty: tty to reset
598 *
599 * Restore a terminal to the driver default state.
600 */
601
602static void tty_reset_termios(struct tty_struct *tty)
603{
604 down_write(&tty->termios_rwsem);
605 tty->termios = tty->driver->init_termios;
606 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
607 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
608 up_write(&tty->termios_rwsem);
609}
610
611
612/**
613 * tty_ldisc_reinit - reinitialise the tty ldisc
614 * @tty: tty to reinit
615 * @ldisc: line discipline to reinitialize
616 *
617 * Switch the tty to a line discipline and leave the ldisc
618 * state closed
619 */
620
621static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
622{
623 struct tty_ldisc *ld = tty_ldisc_get(tty, ldisc);
624
625 if (IS_ERR(ld))
626 return -1;
627
628 tty_ldisc_close(tty, tty->ldisc);
629 tty_ldisc_put(tty->ldisc);
630 /*
631 * Switch the line discipline back
632 */
633 tty->ldisc = ld;
634 tty_set_termios_ldisc(tty, ldisc);
635
636 return 0;
637}
638
639/**
640 * tty_ldisc_hangup - hangup ldisc reset
641 * @tty: tty being hung up
642 *
643 * Some tty devices reset their termios when they receive a hangup
644 * event. In that situation we must also switch back to N_TTY properly
645 * before we reset the termios data.
646 *
647 * Locking: We can take the ldisc mutex as the rest of the code is
648 * careful to allow for this.
649 *
650 * In the pty pair case this occurs in the close() path of the
651 * tty itself so we must be careful about locking rules.
652 */
653
654void tty_ldisc_hangup(struct tty_struct *tty)
655{
656 struct tty_ldisc *ld;
657 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
658 int err = 0;
659
660 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
661
662 ld = tty_ldisc_ref(tty);
663 if (ld != NULL) {
664 if (ld->ops->flush_buffer)
665 ld->ops->flush_buffer(tty);
666 tty_driver_flush_buffer(tty);
667 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
668 ld->ops->write_wakeup)
669 ld->ops->write_wakeup(tty);
670 if (ld->ops->hangup)
671 ld->ops->hangup(tty);
672 tty_ldisc_deref(ld);
673 }
674
675 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
676 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
677
678 tty_unlock(tty);
679
680 /*
681 * Shutdown the current line discipline, and reset it to
682 * N_TTY if need be.
683 *
684 * Avoid racing set_ldisc or tty_ldisc_release
685 */
686 tty_ldisc_lock_pair(tty, tty->link);
687 tty_lock(tty);
688
689 if (tty->ldisc) {
690
691 /* At this point we have a halted ldisc; we want to close it and
692 reopen a new ldisc. We could defer the reopen to the next
693 open but it means auditing a lot of other paths so this is
694 a FIXME */
695 if (reset == 0) {
696
697 if (!tty_ldisc_reinit(tty, tty->termios.c_line))
698 err = tty_ldisc_open(tty, tty->ldisc);
699 else
700 err = 1;
701 }
702 /* If the re-open fails or we reset then go to N_TTY. The
703 N_TTY open cannot fail */
704 if (reset || err) {
705 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
706 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
707 }
708 }
709 tty_ldisc_enable_pair(tty, tty->link);
710 if (reset)
711 tty_reset_termios(tty);
712
713 tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc);
714}
715
716/**
717 * tty_ldisc_setup - open line discipline
718 * @tty: tty being shut down
719 * @o_tty: pair tty for pty/tty pairs
720 *
721 * Called during the initial open of a tty/pty pair in order to set up the
722 * line disciplines and bind them to the tty. This has no locking issues
723 * as the device isn't yet active.
724 */
725
726int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
727{
728 struct tty_ldisc *ld = tty->ldisc;
729 int retval;
730
731 retval = tty_ldisc_open(tty, ld);
732 if (retval)
733 return retval;
734
735 if (o_tty) {
736 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
737 if (retval) {
738 tty_ldisc_close(tty, ld);
739 return retval;
740 }
741 }
742 return 0;
743}
744
745static void tty_ldisc_kill(struct tty_struct *tty)
746{
747 /*
748 * Now kill off the ldisc
749 */
750 tty_ldisc_close(tty, tty->ldisc);
751 tty_ldisc_put(tty->ldisc);
752 /* Force an oops if we mess this up */
753 tty->ldisc = NULL;
754
755 /* Ensure the next open requests the N_TTY ldisc */
756 tty_set_termios_ldisc(tty, N_TTY);
757}
758
759/**
760 * tty_ldisc_release - release line discipline
761 * @tty: tty being shut down
762 * @o_tty: pair tty for pty/tty pairs
763 *
764 * Called during the final close of a tty/pty pair in order to shut down
765 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
766 * ldisc has not been opened.
767 */
768
769void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
770{
771 /*
772 * Shutdown this line discipline. As this is the final close,
773 * it does not race with the set_ldisc code path.
774 */
775
776 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
777
778 tty_ldisc_lock_pair(tty, o_tty);
779 tty_lock_pair(tty, o_tty);
780
781 tty_ldisc_kill(tty);
782 if (o_tty)
783 tty_ldisc_kill(o_tty);
784
785 tty_unlock_pair(tty, o_tty);
786 tty_ldisc_unlock_pair(tty, o_tty);
787
788 /* And the memory resources remaining (buffers, termios) will be
789 disposed of when the kref hits zero */
790
791 tty_ldisc_debug(tty, "ldisc closed\n");
792}
793
794/**
795 * tty_ldisc_init - ldisc setup for new tty
796 * @tty: tty being allocated
797 *
798 * Set up the line discipline objects for a newly allocated tty. Note that
799 * the tty structure is not completely set up when this call is made.
800 */
801
802void tty_ldisc_init(struct tty_struct *tty)
803{
804 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
805 if (IS_ERR(ld))
806 panic("n_tty: init_tty");
807 tty->ldisc = ld;
808}
809
810/**
811 * tty_ldisc_init - ldisc cleanup for new tty
812 * @tty: tty that was allocated recently
813 *
814 * The tty structure must not becompletely set up (tty_ldisc_setup) when
815 * this call is made.
816 */
817void tty_ldisc_deinit(struct tty_struct *tty)
818{
819 tty_ldisc_put(tty->ldisc);
820 tty->ldisc = NULL;
821}
822
823void tty_ldisc_begin(void)
824{
825 /* Setup the default TTY line discipline. */
826 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
827}