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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
159static int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
160
161static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
162{
163 struct tty_ldisc *ld;
164 struct tty_ldisc_ops *ldops;
165
166 if (disc < N_TTY || disc >= NR_LDISCS)
167 return ERR_PTR(-EINVAL);
168
169 /*
170 * Get the ldisc ops - we may need to request them to be loaded
171 * dynamically and try again.
172 */
173 ldops = get_ldops(disc);
174 if (IS_ERR(ldops)) {
175 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
176 return ERR_PTR(-EPERM);
177 request_module("tty-ldisc-%d", disc);
178 ldops = get_ldops(disc);
179 if (IS_ERR(ldops))
180 return ERR_CAST(ldops);
181 }
182
183 /*
184 * There is no way to handle allocation failure of only 16 bytes.
185 * Let's simplify error handling and save more memory.
186 */
187 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
188 ld->ops = ldops;
189 ld->tty = tty;
190
191 return ld;
192}
193
194/**
195 * tty_ldisc_put - release the ldisc
196 *
197 * Complement of tty_ldisc_get().
198 */
199static void tty_ldisc_put(struct tty_ldisc *ld)
200{
201 if (WARN_ON_ONCE(!ld))
202 return;
203
204 put_ldops(ld->ops);
205 kfree(ld);
206}
207
208static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
209{
210 return (*pos < NR_LDISCS) ? pos : NULL;
211}
212
213static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
214{
215 (*pos)++;
216 return (*pos < NR_LDISCS) ? pos : NULL;
217}
218
219static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
220{
221}
222
223static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
224{
225 int i = *(loff_t *)v;
226 struct tty_ldisc_ops *ldops;
227
228 ldops = get_ldops(i);
229 if (IS_ERR(ldops))
230 return 0;
231 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
232 put_ldops(ldops);
233 return 0;
234}
235
236const struct seq_operations tty_ldiscs_seq_ops = {
237 .start = tty_ldiscs_seq_start,
238 .next = tty_ldiscs_seq_next,
239 .stop = tty_ldiscs_seq_stop,
240 .show = tty_ldiscs_seq_show,
241};
242
243/**
244 * tty_ldisc_ref_wait - wait for the tty ldisc
245 * @tty: tty device
246 *
247 * Dereference the line discipline for the terminal and take a
248 * reference to it. If the line discipline is in flux then
249 * wait patiently until it changes.
250 *
251 * Returns: NULL if the tty has been hungup and not re-opened with
252 * a new file descriptor, otherwise valid ldisc reference
253 *
254 * Note: Must not be called from an IRQ/timer context. The caller
255 * must also be careful not to hold other locks that will deadlock
256 * against a discipline change, such as an existing ldisc reference
257 * (which we check for)
258 *
259 * Note: a file_operations routine (read/poll/write) should use this
260 * function to wait for any ldisc lifetime events to finish.
261 */
262
263struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
264{
265 struct tty_ldisc *ld;
266
267 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
268 ld = tty->ldisc;
269 if (!ld)
270 ldsem_up_read(&tty->ldisc_sem);
271 return ld;
272}
273EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
274
275/**
276 * tty_ldisc_ref - get the tty ldisc
277 * @tty: tty device
278 *
279 * Dereference the line discipline for the terminal and take a
280 * reference to it. If the line discipline is in flux then
281 * return NULL. Can be called from IRQ and timer functions.
282 */
283
284struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
285{
286 struct tty_ldisc *ld = NULL;
287
288 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
289 ld = tty->ldisc;
290 if (!ld)
291 ldsem_up_read(&tty->ldisc_sem);
292 }
293 return ld;
294}
295EXPORT_SYMBOL_GPL(tty_ldisc_ref);
296
297/**
298 * tty_ldisc_deref - free a tty ldisc reference
299 * @ld: reference to free up
300 *
301 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
302 * be called in IRQ context.
303 */
304
305void tty_ldisc_deref(struct tty_ldisc *ld)
306{
307 ldsem_up_read(&ld->tty->ldisc_sem);
308}
309EXPORT_SYMBOL_GPL(tty_ldisc_deref);
310
311
312static inline int
313__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
314{
315 return ldsem_down_write(&tty->ldisc_sem, timeout);
316}
317
318static inline int
319__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
320{
321 return ldsem_down_write_nested(&tty->ldisc_sem,
322 LDISC_SEM_OTHER, timeout);
323}
324
325static inline void __tty_ldisc_unlock(struct tty_struct *tty)
326{
327 ldsem_up_write(&tty->ldisc_sem);
328}
329
330int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
331{
332 int ret;
333
334 /* Kindly asking blocked readers to release the read side */
335 set_bit(TTY_LDISC_CHANGING, &tty->flags);
336 wake_up_interruptible_all(&tty->read_wait);
337 wake_up_interruptible_all(&tty->write_wait);
338
339 ret = __tty_ldisc_lock(tty, timeout);
340 if (!ret)
341 return -EBUSY;
342 set_bit(TTY_LDISC_HALTED, &tty->flags);
343 return 0;
344}
345
346void tty_ldisc_unlock(struct tty_struct *tty)
347{
348 clear_bit(TTY_LDISC_HALTED, &tty->flags);
349 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
350 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
351 __tty_ldisc_unlock(tty);
352}
353
354static int
355tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
356 unsigned long timeout)
357{
358 int ret;
359
360 if (tty < tty2) {
361 ret = __tty_ldisc_lock(tty, timeout);
362 if (ret) {
363 ret = __tty_ldisc_lock_nested(tty2, timeout);
364 if (!ret)
365 __tty_ldisc_unlock(tty);
366 }
367 } else {
368 /* if this is possible, it has lots of implications */
369 WARN_ON_ONCE(tty == tty2);
370 if (tty2 && tty != tty2) {
371 ret = __tty_ldisc_lock(tty2, timeout);
372 if (ret) {
373 ret = __tty_ldisc_lock_nested(tty, timeout);
374 if (!ret)
375 __tty_ldisc_unlock(tty2);
376 }
377 } else
378 ret = __tty_ldisc_lock(tty, timeout);
379 }
380
381 if (!ret)
382 return -EBUSY;
383
384 set_bit(TTY_LDISC_HALTED, &tty->flags);
385 if (tty2)
386 set_bit(TTY_LDISC_HALTED, &tty2->flags);
387 return 0;
388}
389
390static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
391{
392 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
393}
394
395static void tty_ldisc_unlock_pair(struct tty_struct *tty,
396 struct tty_struct *tty2)
397{
398 __tty_ldisc_unlock(tty);
399 if (tty2)
400 __tty_ldisc_unlock(tty2);
401}
402
403/**
404 * tty_ldisc_flush - flush line discipline queue
405 * @tty: tty
406 *
407 * Flush the line discipline queue (if any) and the tty flip buffers
408 * for this tty.
409 */
410
411void tty_ldisc_flush(struct tty_struct *tty)
412{
413 struct tty_ldisc *ld = tty_ldisc_ref(tty);
414
415 tty_buffer_flush(tty, ld);
416 if (ld)
417 tty_ldisc_deref(ld);
418}
419EXPORT_SYMBOL_GPL(tty_ldisc_flush);
420
421/**
422 * tty_set_termios_ldisc - set ldisc field
423 * @tty: tty structure
424 * @disc: line discipline number
425 *
426 * This is probably overkill for real world processors but
427 * they are not on hot paths so a little discipline won't do
428 * any harm.
429 *
430 * The line discipline-related tty_struct fields are reset to
431 * prevent the ldisc driver from re-using stale information for
432 * the new ldisc instance.
433 *
434 * Locking: takes termios_rwsem
435 */
436
437static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
438{
439 down_write(&tty->termios_rwsem);
440 tty->termios.c_line = disc;
441 up_write(&tty->termios_rwsem);
442
443 tty->disc_data = NULL;
444 tty->receive_room = 0;
445}
446
447/**
448 * tty_ldisc_open - open a line discipline
449 * @tty: tty we are opening the ldisc on
450 * @ld: discipline to open
451 *
452 * A helper opening method. Also a convenient debugging and check
453 * point.
454 *
455 * Locking: always called with BTM already held.
456 */
457
458static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
459{
460 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
461 if (ld->ops->open) {
462 int ret;
463 /* BTM here locks versus a hangup event */
464 ret = ld->ops->open(tty);
465 if (ret)
466 clear_bit(TTY_LDISC_OPEN, &tty->flags);
467
468 tty_ldisc_debug(tty, "%p: opened\n", ld);
469 return ret;
470 }
471 return 0;
472}
473
474/**
475 * tty_ldisc_close - close a line discipline
476 * @tty: tty we are opening the ldisc on
477 * @ld: discipline to close
478 *
479 * A helper close method. Also a convenient debugging and check
480 * point.
481 */
482
483static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
484{
485 lockdep_assert_held_write(&tty->ldisc_sem);
486 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
487 clear_bit(TTY_LDISC_OPEN, &tty->flags);
488 if (ld->ops->close)
489 ld->ops->close(tty);
490 tty_ldisc_debug(tty, "%p: closed\n", ld);
491}
492
493/**
494 * tty_ldisc_failto - helper for ldisc failback
495 * @tty: tty to open the ldisc on
496 * @ld: ldisc we are trying to fail back to
497 *
498 * Helper to try and recover a tty when switching back to the old
499 * ldisc fails and we need something attached.
500 */
501
502static int tty_ldisc_failto(struct tty_struct *tty, int ld)
503{
504 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
505 int r;
506
507 lockdep_assert_held_write(&tty->ldisc_sem);
508 if (IS_ERR(disc))
509 return PTR_ERR(disc);
510 tty->ldisc = disc;
511 tty_set_termios_ldisc(tty, ld);
512 if ((r = tty_ldisc_open(tty, disc)) < 0)
513 tty_ldisc_put(disc);
514 return r;
515}
516
517/**
518 * tty_ldisc_restore - helper for tty ldisc change
519 * @tty: tty to recover
520 * @old: previous ldisc
521 *
522 * Restore the previous line discipline or N_TTY when a line discipline
523 * change fails due to an open error
524 */
525
526static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
527{
528 /* There is an outstanding reference here so this is safe */
529 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
530 const char *name = tty_name(tty);
531
532 pr_warn("Falling back ldisc for %s.\n", name);
533 /* The traditional behaviour is to fall back to N_TTY, we
534 want to avoid falling back to N_NULL unless we have no
535 choice to avoid the risk of breaking anything */
536 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
537 tty_ldisc_failto(tty, N_NULL) < 0)
538 panic("Couldn't open N_NULL ldisc for %s.", name);
539 }
540}
541
542/**
543 * tty_set_ldisc - set line discipline
544 * @tty: the terminal to set
545 * @ldisc: the line discipline
546 *
547 * Set the discipline of a tty line. Must be called from a process
548 * context. The ldisc change logic has to protect itself against any
549 * overlapping ldisc change (including on the other end of pty pairs),
550 * the close of one side of a tty/pty pair, and eventually hangup.
551 */
552
553int tty_set_ldisc(struct tty_struct *tty, int disc)
554{
555 int retval;
556 struct tty_ldisc *old_ldisc, *new_ldisc;
557
558 new_ldisc = tty_ldisc_get(tty, disc);
559 if (IS_ERR(new_ldisc))
560 return PTR_ERR(new_ldisc);
561
562 tty_lock(tty);
563 retval = tty_ldisc_lock(tty, 5 * HZ);
564 if (retval)
565 goto err;
566
567 if (!tty->ldisc) {
568 retval = -EIO;
569 goto out;
570 }
571
572 /* Check the no-op case */
573 if (tty->ldisc->ops->num == disc)
574 goto out;
575
576 if (test_bit(TTY_HUPPED, &tty->flags)) {
577 /* We were raced by hangup */
578 retval = -EIO;
579 goto out;
580 }
581
582 old_ldisc = tty->ldisc;
583
584 /* Shutdown the old discipline. */
585 tty_ldisc_close(tty, old_ldisc);
586
587 /* Now set up the new line discipline. */
588 tty->ldisc = new_ldisc;
589 tty_set_termios_ldisc(tty, disc);
590
591 retval = tty_ldisc_open(tty, new_ldisc);
592 if (retval < 0) {
593 /* Back to the old one or N_TTY if we can't */
594 tty_ldisc_put(new_ldisc);
595 tty_ldisc_restore(tty, old_ldisc);
596 }
597
598 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
599 down_read(&tty->termios_rwsem);
600 tty->ops->set_ldisc(tty);
601 up_read(&tty->termios_rwsem);
602 }
603
604 /* At this point we hold a reference to the new ldisc and a
605 reference to the old ldisc, or we hold two references to
606 the old ldisc (if it was restored as part of error cleanup
607 above). In either case, releasing a single reference from
608 the old ldisc is correct. */
609 new_ldisc = old_ldisc;
610out:
611 tty_ldisc_unlock(tty);
612
613 /* Restart the work queue in case no characters kick it off. Safe if
614 already running */
615 tty_buffer_restart_work(tty->port);
616err:
617 tty_ldisc_put(new_ldisc); /* drop the extra reference */
618 tty_unlock(tty);
619 return retval;
620}
621EXPORT_SYMBOL_GPL(tty_set_ldisc);
622
623/**
624 * tty_ldisc_kill - teardown ldisc
625 * @tty: tty being released
626 *
627 * Perform final close of the ldisc and reset tty->ldisc
628 */
629static void tty_ldisc_kill(struct tty_struct *tty)
630{
631 lockdep_assert_held_write(&tty->ldisc_sem);
632 if (!tty->ldisc)
633 return;
634 /*
635 * Now kill off the ldisc
636 */
637 tty_ldisc_close(tty, tty->ldisc);
638 tty_ldisc_put(tty->ldisc);
639 /* Force an oops if we mess this up */
640 tty->ldisc = NULL;
641}
642
643/**
644 * tty_reset_termios - reset terminal state
645 * @tty: tty to reset
646 *
647 * Restore a terminal to the driver default state.
648 */
649
650static void tty_reset_termios(struct tty_struct *tty)
651{
652 down_write(&tty->termios_rwsem);
653 tty->termios = tty->driver->init_termios;
654 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
655 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
656 up_write(&tty->termios_rwsem);
657}
658
659
660/**
661 * tty_ldisc_reinit - reinitialise the tty ldisc
662 * @tty: tty to reinit
663 * @disc: line discipline to reinitialize
664 *
665 * Completely reinitialize the line discipline state, by closing the
666 * current instance, if there is one, and opening a new instance. If
667 * an error occurs opening the new non-N_TTY instance, the instance
668 * is dropped and tty->ldisc reset to NULL. The caller can then retry
669 * with N_TTY instead.
670 *
671 * Returns 0 if successful, otherwise error code < 0
672 */
673
674int tty_ldisc_reinit(struct tty_struct *tty, int disc)
675{
676 struct tty_ldisc *ld;
677 int retval;
678
679 lockdep_assert_held_write(&tty->ldisc_sem);
680 ld = tty_ldisc_get(tty, disc);
681 if (IS_ERR(ld)) {
682 BUG_ON(disc == N_TTY);
683 return PTR_ERR(ld);
684 }
685
686 if (tty->ldisc) {
687 tty_ldisc_close(tty, tty->ldisc);
688 tty_ldisc_put(tty->ldisc);
689 }
690
691 /* switch the line discipline */
692 tty->ldisc = ld;
693 tty_set_termios_ldisc(tty, disc);
694 retval = tty_ldisc_open(tty, tty->ldisc);
695 if (retval) {
696 tty_ldisc_put(tty->ldisc);
697 tty->ldisc = NULL;
698 }
699 return retval;
700}
701
702/**
703 * tty_ldisc_hangup - hangup ldisc reset
704 * @tty: tty being hung up
705 *
706 * Some tty devices reset their termios when they receive a hangup
707 * event. In that situation we must also switch back to N_TTY properly
708 * before we reset the termios data.
709 *
710 * Locking: We can take the ldisc mutex as the rest of the code is
711 * careful to allow for this.
712 *
713 * In the pty pair case this occurs in the close() path of the
714 * tty itself so we must be careful about locking rules.
715 */
716
717void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
718{
719 struct tty_ldisc *ld;
720
721 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
722
723 ld = tty_ldisc_ref(tty);
724 if (ld != NULL) {
725 if (ld->ops->flush_buffer)
726 ld->ops->flush_buffer(tty);
727 tty_driver_flush_buffer(tty);
728 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
729 ld->ops->write_wakeup)
730 ld->ops->write_wakeup(tty);
731 if (ld->ops->hangup)
732 ld->ops->hangup(tty);
733 tty_ldisc_deref(ld);
734 }
735
736 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
737 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
738
739 /*
740 * Shutdown the current line discipline, and reset it to
741 * N_TTY if need be.
742 *
743 * Avoid racing set_ldisc or tty_ldisc_release
744 */
745 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
746
747 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
748 tty_reset_termios(tty);
749
750 if (tty->ldisc) {
751 if (reinit) {
752 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
753 tty_ldisc_reinit(tty, N_TTY) < 0)
754 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
755 } else
756 tty_ldisc_kill(tty);
757 }
758 tty_ldisc_unlock(tty);
759}
760
761/**
762 * tty_ldisc_setup - open line discipline
763 * @tty: tty being shut down
764 * @o_tty: pair tty for pty/tty pairs
765 *
766 * Called during the initial open of a tty/pty pair in order to set up the
767 * line disciplines and bind them to the tty. This has no locking issues
768 * as the device isn't yet active.
769 */
770
771int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
772{
773 int retval = tty_ldisc_open(tty, tty->ldisc);
774 if (retval)
775 return retval;
776
777 if (o_tty) {
778 /*
779 * Called without o_tty->ldisc_sem held, as o_tty has been
780 * just allocated and no one has a reference to it.
781 */
782 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
783 if (retval) {
784 tty_ldisc_close(tty, tty->ldisc);
785 return retval;
786 }
787 }
788 return 0;
789}
790
791/**
792 * tty_ldisc_release - release line discipline
793 * @tty: tty being shut down (or one end of pty pair)
794 *
795 * Called during the final close of a tty or a pty pair in order to shut
796 * down the line discpline layer. On exit, each tty's ldisc is NULL.
797 */
798
799void tty_ldisc_release(struct tty_struct *tty)
800{
801 struct tty_struct *o_tty = tty->link;
802
803 /*
804 * Shutdown this line discipline. As this is the final close,
805 * it does not race with the set_ldisc code path.
806 */
807
808 tty_ldisc_lock_pair(tty, o_tty);
809 tty_ldisc_kill(tty);
810 if (o_tty)
811 tty_ldisc_kill(o_tty);
812 tty_ldisc_unlock_pair(tty, o_tty);
813
814 /* And the memory resources remaining (buffers, termios) will be
815 disposed of when the kref hits zero */
816
817 tty_ldisc_debug(tty, "released\n");
818}
819EXPORT_SYMBOL_GPL(tty_ldisc_release);
820
821/**
822 * tty_ldisc_init - ldisc setup for new tty
823 * @tty: tty being allocated
824 *
825 * Set up the line discipline objects for a newly allocated tty. Note that
826 * the tty structure is not completely set up when this call is made.
827 */
828
829int tty_ldisc_init(struct tty_struct *tty)
830{
831 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
832 if (IS_ERR(ld))
833 return PTR_ERR(ld);
834 tty->ldisc = ld;
835 return 0;
836}
837
838/**
839 * tty_ldisc_deinit - ldisc cleanup for new tty
840 * @tty: tty that was allocated recently
841 *
842 * The tty structure must not becompletely set up (tty_ldisc_setup) when
843 * this call is made.
844 */
845void tty_ldisc_deinit(struct tty_struct *tty)
846{
847 /* no ldisc_sem, tty is being destroyed */
848 if (tty->ldisc)
849 tty_ldisc_put(tty->ldisc);
850 tty->ldisc = NULL;
851}
852
853static struct ctl_table tty_table[] = {
854 {
855 .procname = "ldisc_autoload",
856 .data = &tty_ldisc_autoload,
857 .maxlen = sizeof(tty_ldisc_autoload),
858 .mode = 0644,
859 .proc_handler = proc_dointvec,
860 .extra1 = SYSCTL_ZERO,
861 .extra2 = SYSCTL_ONE,
862 },
863 { }
864};
865
866static struct ctl_table tty_dir_table[] = {
867 {
868 .procname = "tty",
869 .mode = 0555,
870 .child = tty_table,
871 },
872 { }
873};
874
875static struct ctl_table tty_root_table[] = {
876 {
877 .procname = "dev",
878 .mode = 0555,
879 .child = tty_dir_table,
880 },
881 { }
882};
883
884void tty_sysctl_init(void)
885{
886 register_sysctl_table(tty_root_table);
887}
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/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>
22
23/*
24 * This guards the refcounted line discipline lists. The lock
25 * must be taken with irqs off because there are hangup path
26 * callers who will do ldisc lookups and cannot sleep.
27 */
28
29static DEFINE_SPINLOCK(tty_ldisc_lock);
30static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
31/* Line disc dispatch table */
32static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
33
34static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
35{
36 if (ld)
37 atomic_inc(&ld->users);
38 return ld;
39}
40
41static void put_ldisc(struct tty_ldisc *ld)
42{
43 unsigned long flags;
44
45 if (WARN_ON_ONCE(!ld))
46 return;
47
48 /*
49 * If this is the last user, free the ldisc, and
50 * release the ldisc ops.
51 *
52 * We really want an "atomic_dec_and_lock_irqsave()",
53 * but we don't have it, so this does it by hand.
54 */
55 local_irq_save(flags);
56 if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
57 struct tty_ldisc_ops *ldo = ld->ops;
58
59 ldo->refcount--;
60 module_put(ldo->owner);
61 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
62
63 kfree(ld);
64 return;
65 }
66 local_irq_restore(flags);
67 wake_up(&ld->wq_idle);
68}
69
70/**
71 * tty_register_ldisc - install a line discipline
72 * @disc: ldisc number
73 * @new_ldisc: pointer to the ldisc object
74 *
75 * Installs a new line discipline into the kernel. The discipline
76 * is set up as unreferenced and then made available to the kernel
77 * from this point onwards.
78 *
79 * Locking:
80 * takes tty_ldisc_lock to guard against ldisc races
81 */
82
83int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
84{
85 unsigned long flags;
86 int ret = 0;
87
88 if (disc < N_TTY || disc >= NR_LDISCS)
89 return -EINVAL;
90
91 spin_lock_irqsave(&tty_ldisc_lock, flags);
92 tty_ldiscs[disc] = new_ldisc;
93 new_ldisc->num = disc;
94 new_ldisc->refcount = 0;
95 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
96
97 return ret;
98}
99EXPORT_SYMBOL(tty_register_ldisc);
100
101/**
102 * tty_unregister_ldisc - unload a line discipline
103 * @disc: ldisc number
104 * @new_ldisc: pointer to the ldisc object
105 *
106 * Remove a line discipline from the kernel providing it is not
107 * currently in use.
108 *
109 * Locking:
110 * takes tty_ldisc_lock to guard against ldisc races
111 */
112
113int tty_unregister_ldisc(int disc)
114{
115 unsigned long flags;
116 int ret = 0;
117
118 if (disc < N_TTY || disc >= NR_LDISCS)
119 return -EINVAL;
120
121 spin_lock_irqsave(&tty_ldisc_lock, flags);
122 if (tty_ldiscs[disc]->refcount)
123 ret = -EBUSY;
124 else
125 tty_ldiscs[disc] = NULL;
126 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
127
128 return ret;
129}
130EXPORT_SYMBOL(tty_unregister_ldisc);
131
132static struct tty_ldisc_ops *get_ldops(int disc)
133{
134 unsigned long flags;
135 struct tty_ldisc_ops *ldops, *ret;
136
137 spin_lock_irqsave(&tty_ldisc_lock, flags);
138 ret = ERR_PTR(-EINVAL);
139 ldops = tty_ldiscs[disc];
140 if (ldops) {
141 ret = ERR_PTR(-EAGAIN);
142 if (try_module_get(ldops->owner)) {
143 ldops->refcount++;
144 ret = ldops;
145 }
146 }
147 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
148 return ret;
149}
150
151static void put_ldops(struct tty_ldisc_ops *ldops)
152{
153 unsigned long flags;
154
155 spin_lock_irqsave(&tty_ldisc_lock, flags);
156 ldops->refcount--;
157 module_put(ldops->owner);
158 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
159}
160
161/**
162 * tty_ldisc_get - take a reference to an ldisc
163 * @disc: ldisc number
164 *
165 * Takes a reference to a line discipline. Deals with refcounts and
166 * module locking counts. Returns NULL if the discipline is not available.
167 * Returns a pointer to the discipline and bumps the ref count if it is
168 * available
169 *
170 * Locking:
171 * takes tty_ldisc_lock to guard against ldisc races
172 */
173
174static struct tty_ldisc *tty_ldisc_get(int disc)
175{
176 struct tty_ldisc *ld;
177 struct tty_ldisc_ops *ldops;
178
179 if (disc < N_TTY || disc >= NR_LDISCS)
180 return ERR_PTR(-EINVAL);
181
182 /*
183 * Get the ldisc ops - we may need to request them to be loaded
184 * dynamically and try again.
185 */
186 ldops = get_ldops(disc);
187 if (IS_ERR(ldops)) {
188 request_module("tty-ldisc-%d", disc);
189 ldops = get_ldops(disc);
190 if (IS_ERR(ldops))
191 return ERR_CAST(ldops);
192 }
193
194 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
195 if (ld == NULL) {
196 put_ldops(ldops);
197 return ERR_PTR(-ENOMEM);
198 }
199
200 ld->ops = ldops;
201 atomic_set(&ld->users, 1);
202 init_waitqueue_head(&ld->wq_idle);
203
204 return ld;
205}
206
207static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
208{
209 return (*pos < NR_LDISCS) ? pos : NULL;
210}
211
212static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
213{
214 (*pos)++;
215 return (*pos < NR_LDISCS) ? pos : NULL;
216}
217
218static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
219{
220}
221
222static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
223{
224 int i = *(loff_t *)v;
225 struct tty_ldisc_ops *ldops;
226
227 ldops = get_ldops(i);
228 if (IS_ERR(ldops))
229 return 0;
230 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
231 put_ldops(ldops);
232 return 0;
233}
234
235static const struct seq_operations tty_ldiscs_seq_ops = {
236 .start = tty_ldiscs_seq_start,
237 .next = tty_ldiscs_seq_next,
238 .stop = tty_ldiscs_seq_stop,
239 .show = tty_ldiscs_seq_show,
240};
241
242static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
243{
244 return seq_open(file, &tty_ldiscs_seq_ops);
245}
246
247const struct file_operations tty_ldiscs_proc_fops = {
248 .owner = THIS_MODULE,
249 .open = proc_tty_ldiscs_open,
250 .read = seq_read,
251 .llseek = seq_lseek,
252 .release = seq_release,
253};
254
255/**
256 * tty_ldisc_assign - set ldisc on a tty
257 * @tty: tty to assign
258 * @ld: line discipline
259 *
260 * Install an instance of a line discipline into a tty structure. The
261 * ldisc must have a reference count above zero to ensure it remains.
262 * The tty instance refcount starts at zero.
263 *
264 * Locking:
265 * Caller must hold references
266 */
267
268static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
269{
270 tty->ldisc = ld;
271}
272
273/**
274 * tty_ldisc_try - internal helper
275 * @tty: the tty
276 *
277 * Make a single attempt to grab and bump the refcount on
278 * the tty ldisc. Return 0 on failure or 1 on success. This is
279 * used to implement both the waiting and non waiting versions
280 * of tty_ldisc_ref
281 *
282 * Locking: takes tty_ldisc_lock
283 */
284
285static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
286{
287 unsigned long flags;
288 struct tty_ldisc *ld;
289
290 spin_lock_irqsave(&tty_ldisc_lock, flags);
291 ld = NULL;
292 if (test_bit(TTY_LDISC, &tty->flags))
293 ld = get_ldisc(tty->ldisc);
294 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
295 return ld;
296}
297
298/**
299 * tty_ldisc_ref_wait - wait for the tty ldisc
300 * @tty: tty device
301 *
302 * Dereference the line discipline for the terminal and take a
303 * reference to it. If the line discipline is in flux then
304 * wait patiently until it changes.
305 *
306 * Note: Must not be called from an IRQ/timer context. The caller
307 * must also be careful not to hold other locks that will deadlock
308 * against a discipline change, such as an existing ldisc reference
309 * (which we check for)
310 *
311 * Locking: call functions take tty_ldisc_lock
312 */
313
314struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
315{
316 struct tty_ldisc *ld;
317
318 /* wait_event is a macro */
319 wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
320 return ld;
321}
322EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
323
324/**
325 * tty_ldisc_ref - get the tty ldisc
326 * @tty: tty device
327 *
328 * Dereference the line discipline for the terminal and take a
329 * reference to it. If the line discipline is in flux then
330 * return NULL. Can be called from IRQ and timer functions.
331 *
332 * Locking: called functions take tty_ldisc_lock
333 */
334
335struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
336{
337 return tty_ldisc_try(tty);
338}
339EXPORT_SYMBOL_GPL(tty_ldisc_ref);
340
341/**
342 * tty_ldisc_deref - free a tty ldisc reference
343 * @ld: reference to free up
344 *
345 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
346 * be called in IRQ context.
347 *
348 * Locking: takes tty_ldisc_lock
349 */
350
351void tty_ldisc_deref(struct tty_ldisc *ld)
352{
353 put_ldisc(ld);
354}
355EXPORT_SYMBOL_GPL(tty_ldisc_deref);
356
357static inline void tty_ldisc_put(struct tty_ldisc *ld)
358{
359 put_ldisc(ld);
360}
361
362/**
363 * tty_ldisc_enable - allow ldisc use
364 * @tty: terminal to activate ldisc on
365 *
366 * Set the TTY_LDISC flag when the line discipline can be called
367 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
368 * changing flag to indicate any ldisc change is now over.
369 *
370 * Note: nobody should set the TTY_LDISC bit except via this function.
371 * Clearing directly is allowed.
372 */
373
374void tty_ldisc_enable(struct tty_struct *tty)
375{
376 set_bit(TTY_LDISC, &tty->flags);
377 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
378 wake_up(&tty_ldisc_wait);
379}
380
381/**
382 * tty_ldisc_flush - flush line discipline queue
383 * @tty: tty
384 *
385 * Flush the line discipline queue (if any) for this tty. If there
386 * is no line discipline active this is a no-op.
387 */
388
389void tty_ldisc_flush(struct tty_struct *tty)
390{
391 struct tty_ldisc *ld = tty_ldisc_ref(tty);
392 if (ld) {
393 if (ld->ops->flush_buffer)
394 ld->ops->flush_buffer(tty);
395 tty_ldisc_deref(ld);
396 }
397 tty_buffer_flush(tty);
398}
399EXPORT_SYMBOL_GPL(tty_ldisc_flush);
400
401/**
402 * tty_set_termios_ldisc - set ldisc field
403 * @tty: tty structure
404 * @num: line discipline number
405 *
406 * This is probably overkill for real world processors but
407 * they are not on hot paths so a little discipline won't do
408 * any harm.
409 *
410 * Locking: takes termios_mutex
411 */
412
413static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
414{
415 mutex_lock(&tty->termios_mutex);
416 tty->termios->c_line = num;
417 mutex_unlock(&tty->termios_mutex);
418}
419
420/**
421 * tty_ldisc_open - open a line discipline
422 * @tty: tty we are opening the ldisc on
423 * @ld: discipline to open
424 *
425 * A helper opening method. Also a convenient debugging and check
426 * point.
427 *
428 * Locking: always called with BTM already held.
429 */
430
431static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
432{
433 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
434 if (ld->ops->open) {
435 int ret;
436 /* BTM here locks versus a hangup event */
437 ret = ld->ops->open(tty);
438 if (ret)
439 clear_bit(TTY_LDISC_OPEN, &tty->flags);
440 return ret;
441 }
442 return 0;
443}
444
445/**
446 * tty_ldisc_close - close a line discipline
447 * @tty: tty we are opening the ldisc on
448 * @ld: discipline to close
449 *
450 * A helper close method. Also a convenient debugging and check
451 * point.
452 */
453
454static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
455{
456 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
457 clear_bit(TTY_LDISC_OPEN, &tty->flags);
458 if (ld->ops->close)
459 ld->ops->close(tty);
460}
461
462/**
463 * tty_ldisc_restore - helper for tty ldisc change
464 * @tty: tty to recover
465 * @old: previous ldisc
466 *
467 * Restore the previous line discipline or N_TTY when a line discipline
468 * change fails due to an open error
469 */
470
471static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
472{
473 char buf[64];
474 struct tty_ldisc *new_ldisc;
475 int r;
476
477 /* There is an outstanding reference here so this is safe */
478 old = tty_ldisc_get(old->ops->num);
479 WARN_ON(IS_ERR(old));
480 tty_ldisc_assign(tty, old);
481 tty_set_termios_ldisc(tty, old->ops->num);
482 if (tty_ldisc_open(tty, old) < 0) {
483 tty_ldisc_put(old);
484 /* This driver is always present */
485 new_ldisc = tty_ldisc_get(N_TTY);
486 if (IS_ERR(new_ldisc))
487 panic("n_tty: get");
488 tty_ldisc_assign(tty, new_ldisc);
489 tty_set_termios_ldisc(tty, N_TTY);
490 r = tty_ldisc_open(tty, new_ldisc);
491 if (r < 0)
492 panic("Couldn't open N_TTY ldisc for "
493 "%s --- error %d.",
494 tty_name(tty, buf), r);
495 }
496}
497
498/**
499 * tty_ldisc_halt - shut down the line discipline
500 * @tty: tty device
501 *
502 * Shut down the line discipline and work queue for this tty device.
503 * The TTY_LDISC flag being cleared ensures no further references can
504 * be obtained while the delayed work queue halt ensures that no more
505 * data is fed to the ldisc.
506 *
507 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
508 * in order to make sure any currently executing ldisc work is also
509 * flushed.
510 */
511
512static int tty_ldisc_halt(struct tty_struct *tty)
513{
514 clear_bit(TTY_LDISC, &tty->flags);
515 return cancel_work_sync(&tty->buf.work);
516}
517
518/**
519 * tty_ldisc_flush_works - flush all works of a tty
520 * @tty: tty device to flush works for
521 *
522 * Sync flush all works belonging to @tty.
523 */
524static void tty_ldisc_flush_works(struct tty_struct *tty)
525{
526 flush_work_sync(&tty->hangup_work);
527 flush_work_sync(&tty->SAK_work);
528 flush_work_sync(&tty->buf.work);
529}
530
531/**
532 * tty_ldisc_wait_idle - wait for the ldisc to become idle
533 * @tty: tty to wait for
534 * @timeout: for how long to wait at most
535 *
536 * Wait for the line discipline to become idle. The discipline must
537 * have been halted for this to guarantee it remains idle.
538 */
539static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
540{
541 long ret;
542 ret = wait_event_timeout(tty->ldisc->wq_idle,
543 atomic_read(&tty->ldisc->users) == 1, timeout);
544 return ret > 0 ? 0 : -EBUSY;
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 * Locking: takes tty_ldisc_lock, termios_mutex
558 */
559
560int tty_set_ldisc(struct tty_struct *tty, int ldisc)
561{
562 int retval;
563 struct tty_ldisc *o_ldisc, *new_ldisc;
564 int work, o_work = 0;
565 struct tty_struct *o_tty;
566
567 new_ldisc = tty_ldisc_get(ldisc);
568 if (IS_ERR(new_ldisc))
569 return PTR_ERR(new_ldisc);
570
571 tty_lock();
572 /*
573 * We need to look at the tty locking here for pty/tty pairs
574 * when both sides try to change in parallel.
575 */
576
577 o_tty = tty->link; /* o_tty is the pty side or NULL */
578
579
580 /*
581 * Check the no-op case
582 */
583
584 if (tty->ldisc->ops->num == ldisc) {
585 tty_unlock();
586 tty_ldisc_put(new_ldisc);
587 return 0;
588 }
589
590 tty_unlock();
591 /*
592 * Problem: What do we do if this blocks ?
593 * We could deadlock here
594 */
595
596 tty_wait_until_sent(tty, 0);
597
598 tty_lock();
599 mutex_lock(&tty->ldisc_mutex);
600
601 /*
602 * We could be midstream of another ldisc change which has
603 * dropped the lock during processing. If so we need to wait.
604 */
605
606 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
607 mutex_unlock(&tty->ldisc_mutex);
608 tty_unlock();
609 wait_event(tty_ldisc_wait,
610 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
611 tty_lock();
612 mutex_lock(&tty->ldisc_mutex);
613 }
614
615 set_bit(TTY_LDISC_CHANGING, &tty->flags);
616
617 /*
618 * No more input please, we are switching. The new ldisc
619 * will update this value in the ldisc open function
620 */
621
622 tty->receive_room = 0;
623
624 o_ldisc = tty->ldisc;
625
626 tty_unlock();
627 /*
628 * Make sure we don't change while someone holds a
629 * reference to the line discipline. The TTY_LDISC bit
630 * prevents anyone taking a reference once it is clear.
631 * We need the lock to avoid racing reference takers.
632 *
633 * We must clear the TTY_LDISC bit here to avoid a livelock
634 * with a userspace app continually trying to use the tty in
635 * parallel to the change and re-referencing the tty.
636 */
637
638 work = tty_ldisc_halt(tty);
639 if (o_tty)
640 o_work = tty_ldisc_halt(o_tty);
641
642 /*
643 * Wait for ->hangup_work and ->buf.work handlers to terminate.
644 * We must drop the mutex here in case a hangup is also in process.
645 */
646
647 mutex_unlock(&tty->ldisc_mutex);
648
649 tty_ldisc_flush_works(tty);
650
651 retval = tty_ldisc_wait_idle(tty, 5 * HZ);
652
653 tty_lock();
654 mutex_lock(&tty->ldisc_mutex);
655
656 /* handle wait idle failure locked */
657 if (retval) {
658 tty_ldisc_put(new_ldisc);
659 goto enable;
660 }
661
662 if (test_bit(TTY_HUPPED, &tty->flags)) {
663 /* We were raced by the hangup method. It will have stomped
664 the ldisc data and closed the ldisc down */
665 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
666 mutex_unlock(&tty->ldisc_mutex);
667 tty_ldisc_put(new_ldisc);
668 tty_unlock();
669 return -EIO;
670 }
671
672 /* Shutdown the current discipline. */
673 tty_ldisc_close(tty, o_ldisc);
674
675 /* Now set up the new line discipline. */
676 tty_ldisc_assign(tty, new_ldisc);
677 tty_set_termios_ldisc(tty, ldisc);
678
679 retval = tty_ldisc_open(tty, new_ldisc);
680 if (retval < 0) {
681 /* Back to the old one or N_TTY if we can't */
682 tty_ldisc_put(new_ldisc);
683 tty_ldisc_restore(tty, o_ldisc);
684 }
685
686 /* At this point we hold a reference to the new ldisc and a
687 a reference to the old ldisc. If we ended up flipping back
688 to the existing ldisc we have two references to it */
689
690 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
691 tty->ops->set_ldisc(tty);
692
693 tty_ldisc_put(o_ldisc);
694
695enable:
696 /*
697 * Allow ldisc referencing to occur again
698 */
699
700 tty_ldisc_enable(tty);
701 if (o_tty)
702 tty_ldisc_enable(o_tty);
703
704 /* Restart the work queue in case no characters kick it off. Safe if
705 already running */
706 if (work)
707 schedule_work(&tty->buf.work);
708 if (o_work)
709 schedule_work(&o_tty->buf.work);
710 mutex_unlock(&tty->ldisc_mutex);
711 tty_unlock();
712 return retval;
713}
714
715/**
716 * tty_reset_termios - reset terminal state
717 * @tty: tty to reset
718 *
719 * Restore a terminal to the driver default state.
720 */
721
722static void tty_reset_termios(struct tty_struct *tty)
723{
724 mutex_lock(&tty->termios_mutex);
725 *tty->termios = tty->driver->init_termios;
726 tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
727 tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
728 mutex_unlock(&tty->termios_mutex);
729}
730
731
732/**
733 * tty_ldisc_reinit - reinitialise the tty ldisc
734 * @tty: tty to reinit
735 * @ldisc: line discipline to reinitialize
736 *
737 * Switch the tty to a line discipline and leave the ldisc
738 * state closed
739 */
740
741static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
742{
743 struct tty_ldisc *ld = tty_ldisc_get(ldisc);
744
745 if (IS_ERR(ld))
746 return -1;
747
748 tty_ldisc_close(tty, tty->ldisc);
749 tty_ldisc_put(tty->ldisc);
750 tty->ldisc = NULL;
751 /*
752 * Switch the line discipline back
753 */
754 tty_ldisc_assign(tty, ld);
755 tty_set_termios_ldisc(tty, ldisc);
756
757 return 0;
758}
759
760/**
761 * tty_ldisc_hangup - hangup ldisc reset
762 * @tty: tty being hung up
763 *
764 * Some tty devices reset their termios when they receive a hangup
765 * event. In that situation we must also switch back to N_TTY properly
766 * before we reset the termios data.
767 *
768 * Locking: We can take the ldisc mutex as the rest of the code is
769 * careful to allow for this.
770 *
771 * In the pty pair case this occurs in the close() path of the
772 * tty itself so we must be careful about locking rules.
773 */
774
775void tty_ldisc_hangup(struct tty_struct *tty)
776{
777 struct tty_ldisc *ld;
778 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
779 int err = 0;
780
781 /*
782 * FIXME! What are the locking issues here? This may me overdoing
783 * things... This question is especially important now that we've
784 * removed the irqlock.
785 */
786 ld = tty_ldisc_ref(tty);
787 if (ld != NULL) {
788 /* We may have no line discipline at this point */
789 if (ld->ops->flush_buffer)
790 ld->ops->flush_buffer(tty);
791 tty_driver_flush_buffer(tty);
792 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
793 ld->ops->write_wakeup)
794 ld->ops->write_wakeup(tty);
795 if (ld->ops->hangup)
796 ld->ops->hangup(tty);
797 tty_ldisc_deref(ld);
798 }
799 /*
800 * FIXME: Once we trust the LDISC code better we can wait here for
801 * ldisc completion and fix the driver call race
802 */
803 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
804 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
805 /*
806 * Shutdown the current line discipline, and reset it to
807 * N_TTY if need be.
808 *
809 * Avoid racing set_ldisc or tty_ldisc_release
810 */
811 mutex_lock(&tty->ldisc_mutex);
812
813 /*
814 * this is like tty_ldisc_halt, but we need to give up
815 * the BTM before calling cancel_work_sync, which may
816 * need to wait for another function taking the BTM
817 */
818 clear_bit(TTY_LDISC, &tty->flags);
819 tty_unlock();
820 cancel_work_sync(&tty->buf.work);
821 mutex_unlock(&tty->ldisc_mutex);
822retry:
823 tty_lock();
824 mutex_lock(&tty->ldisc_mutex);
825
826 /* At this point we have a closed ldisc and we want to
827 reopen it. We could defer this to the next open but
828 it means auditing a lot of other paths so this is
829 a FIXME */
830 if (tty->ldisc) { /* Not yet closed */
831 if (atomic_read(&tty->ldisc->users) != 1) {
832 char cur_n[TASK_COMM_LEN], tty_n[64];
833 long timeout = 3 * HZ;
834 tty_unlock();
835
836 while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
837 timeout = MAX_SCHEDULE_TIMEOUT;
838 printk_ratelimited(KERN_WARNING
839 "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
840 __func__, get_task_comm(cur_n, current),
841 tty_name(tty, tty_n));
842 }
843 mutex_unlock(&tty->ldisc_mutex);
844 goto retry;
845 }
846
847 if (reset == 0) {
848
849 if (!tty_ldisc_reinit(tty, tty->termios->c_line))
850 err = tty_ldisc_open(tty, tty->ldisc);
851 else
852 err = 1;
853 }
854 /* If the re-open fails or we reset then go to N_TTY. The
855 N_TTY open cannot fail */
856 if (reset || err) {
857 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
858 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
859 }
860 tty_ldisc_enable(tty);
861 }
862 mutex_unlock(&tty->ldisc_mutex);
863 if (reset)
864 tty_reset_termios(tty);
865}
866
867/**
868 * tty_ldisc_setup - open line discipline
869 * @tty: tty being shut down
870 * @o_tty: pair tty for pty/tty pairs
871 *
872 * Called during the initial open of a tty/pty pair in order to set up the
873 * line disciplines and bind them to the tty. This has no locking issues
874 * as the device isn't yet active.
875 */
876
877int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
878{
879 struct tty_ldisc *ld = tty->ldisc;
880 int retval;
881
882 retval = tty_ldisc_open(tty, ld);
883 if (retval)
884 return retval;
885
886 if (o_tty) {
887 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
888 if (retval) {
889 tty_ldisc_close(tty, ld);
890 return retval;
891 }
892 tty_ldisc_enable(o_tty);
893 }
894 tty_ldisc_enable(tty);
895 return 0;
896}
897/**
898 * tty_ldisc_release - release line discipline
899 * @tty: tty being shut down
900 * @o_tty: pair tty for pty/tty pairs
901 *
902 * Called during the final close of a tty/pty pair in order to shut down
903 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
904 * ldisc has not been opened.
905 */
906
907void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
908{
909 /*
910 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
911 * kill any delayed work. As this is the final close it does not
912 * race with the set_ldisc code path.
913 */
914
915 tty_unlock();
916 tty_ldisc_halt(tty);
917 tty_ldisc_flush_works(tty);
918 tty_lock();
919
920 mutex_lock(&tty->ldisc_mutex);
921 /*
922 * Now kill off the ldisc
923 */
924 tty_ldisc_close(tty, tty->ldisc);
925 tty_ldisc_put(tty->ldisc);
926 /* Force an oops if we mess this up */
927 tty->ldisc = NULL;
928
929 /* Ensure the next open requests the N_TTY ldisc */
930 tty_set_termios_ldisc(tty, N_TTY);
931 mutex_unlock(&tty->ldisc_mutex);
932
933 /* This will need doing differently if we need to lock */
934 if (o_tty)
935 tty_ldisc_release(o_tty, NULL);
936
937 /* And the memory resources remaining (buffers, termios) will be
938 disposed of when the kref hits zero */
939}
940
941/**
942 * tty_ldisc_init - ldisc setup for new tty
943 * @tty: tty being allocated
944 *
945 * Set up the line discipline objects for a newly allocated tty. Note that
946 * the tty structure is not completely set up when this call is made.
947 */
948
949void tty_ldisc_init(struct tty_struct *tty)
950{
951 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
952 if (IS_ERR(ld))
953 panic("n_tty: init_tty");
954 tty_ldisc_assign(tty, ld);
955}
956
957/**
958 * tty_ldisc_init - ldisc cleanup for new tty
959 * @tty: tty that was allocated recently
960 *
961 * The tty structure must not becompletely set up (tty_ldisc_setup) when
962 * this call is made.
963 */
964void tty_ldisc_deinit(struct tty_struct *tty)
965{
966 put_ldisc(tty->ldisc);
967 tty_ldisc_assign(tty, NULL);
968}
969
970void tty_ldisc_begin(void)
971{
972 /* Setup the default TTY line discipline. */
973 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
974}