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