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