Line data Source code
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 */
33 : enum {
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 :
45 : static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
46 : /* Line disc dispatch table */
47 : static 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 : */
58 0 : int tty_register_ldisc(struct tty_ldisc_ops *new_ldisc)
59 : {
60 0 : unsigned long flags;
61 :
62 0 : if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS)
63 0 : return -EINVAL;
64 :
65 0 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
66 0 : tty_ldiscs[new_ldisc->num] = new_ldisc;
67 0 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
68 :
69 0 : return 0;
70 0 : }
71 : EXPORT_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 :
83 0 : void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc)
84 : {
85 0 : unsigned long flags;
86 :
87 0 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
88 0 : tty_ldiscs[ldisc->num] = NULL;
89 0 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
90 0 : }
91 : EXPORT_SYMBOL(tty_unregister_ldisc);
92 :
93 6 : static struct tty_ldisc_ops *get_ldops(int disc)
94 : {
95 6 : unsigned long flags;
96 6 : struct tty_ldisc_ops *ldops, *ret;
97 :
98 6 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
99 6 : ret = ERR_PTR(-EINVAL);
100 6 : ldops = tty_ldiscs[disc];
101 6 : if (ldops) {
102 6 : ret = ERR_PTR(-EAGAIN);
103 6 : if (try_module_get(ldops->owner))
104 6 : ret = ldops;
105 6 : }
106 6 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107 12 : return ret;
108 6 : }
109 :
110 6 : static void put_ldops(struct tty_ldisc_ops *ldops)
111 : {
112 6 : unsigned long flags;
113 :
114 6 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115 6 : module_put(ldops->owner);
116 6 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
117 6 : }
118 :
119 : int 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 : */
139 6 : static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
140 : {
141 6 : struct tty_ldisc *ld;
142 6 : struct tty_ldisc_ops *ldops;
143 :
144 6 : if (disc < N_TTY || disc >= NR_LDISCS)
145 0 : 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 6 : ldops = get_ldops(disc);
152 6 : if (IS_ERR(ldops)) {
153 0 : if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
154 0 : return ERR_PTR(-EPERM);
155 0 : request_module("tty-ldisc-%d", disc);
156 0 : ldops = get_ldops(disc);
157 0 : if (IS_ERR(ldops))
158 0 : return ERR_CAST(ldops);
159 0 : }
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 6 : ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
166 6 : ld->ops = ldops;
167 6 : ld->tty = tty;
168 :
169 6 : return ld;
170 6 : }
171 :
172 : /**
173 : * tty_ldisc_put - release the ldisc
174 : * @ld: lisdsc to release
175 : *
176 : * Complement of tty_ldisc_get().
177 : */
178 6 : static void tty_ldisc_put(struct tty_ldisc *ld)
179 : {
180 6 : if (WARN_ON_ONCE(!ld))
181 0 : return;
182 :
183 6 : put_ldops(ld->ops);
184 6 : kfree(ld);
185 6 : }
186 :
187 0 : static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
188 : {
189 0 : return (*pos < NR_LDISCS) ? pos : NULL;
190 : }
191 :
192 0 : static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
193 : {
194 0 : (*pos)++;
195 0 : return (*pos < NR_LDISCS) ? pos : NULL;
196 : }
197 :
198 0 : static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
199 : {
200 0 : }
201 :
202 0 : static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
203 : {
204 0 : int i = *(loff_t *)v;
205 0 : struct tty_ldisc_ops *ldops;
206 :
207 0 : ldops = get_ldops(i);
208 0 : if (IS_ERR(ldops))
209 0 : return 0;
210 0 : seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
211 0 : put_ldops(ldops);
212 0 : return 0;
213 0 : }
214 :
215 : const 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 : */
239 159 : struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
240 : {
241 159 : struct tty_ldisc *ld;
242 :
243 159 : ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
244 159 : ld = tty->ldisc;
245 159 : if (!ld)
246 0 : ldsem_up_read(&tty->ldisc_sem);
247 318 : return ld;
248 159 : }
249 : EXPORT_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 : */
259 35 : struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
260 : {
261 35 : struct tty_ldisc *ld = NULL;
262 :
263 35 : if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
264 35 : ld = tty->ldisc;
265 35 : if (!ld)
266 0 : ldsem_up_read(&tty->ldisc_sem);
267 35 : }
268 70 : return ld;
269 35 : }
270 : EXPORT_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 : */
279 195 : void tty_ldisc_deref(struct tty_ldisc *ld)
280 : {
281 195 : ldsem_up_read(&ld->tty->ldisc_sem);
282 195 : }
283 : EXPORT_SYMBOL_GPL(tty_ldisc_deref);
284 :
285 :
286 : static inline int
287 12 : __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
288 : {
289 12 : return ldsem_down_write(&tty->ldisc_sem, timeout);
290 : }
291 :
292 : static inline int
293 0 : __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
294 : {
295 0 : return ldsem_down_write_nested(&tty->ldisc_sem,
296 0 : LDISC_SEM_OTHER, timeout);
297 : }
298 :
299 12 : static inline void __tty_ldisc_unlock(struct tty_struct *tty)
300 : {
301 12 : ldsem_up_write(&tty->ldisc_sem);
302 12 : }
303 :
304 6 : int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
305 : {
306 6 : int ret;
307 :
308 : /* Kindly asking blocked readers to release the read side */
309 6 : set_bit(TTY_LDISC_CHANGING, &tty->flags);
310 6 : wake_up_interruptible_all(&tty->read_wait);
311 6 : wake_up_interruptible_all(&tty->write_wait);
312 :
313 6 : ret = __tty_ldisc_lock(tty, timeout);
314 6 : if (!ret)
315 0 : return -EBUSY;
316 6 : set_bit(TTY_LDISC_HALTED, &tty->flags);
317 6 : return 0;
318 6 : }
319 :
320 6 : void tty_ldisc_unlock(struct tty_struct *tty)
321 : {
322 6 : clear_bit(TTY_LDISC_HALTED, &tty->flags);
323 : /* Can be cleared here - ldisc_unlock will wake up writers firstly */
324 6 : clear_bit(TTY_LDISC_CHANGING, &tty->flags);
325 6 : __tty_ldisc_unlock(tty);
326 6 : }
327 :
328 : static int
329 6 : tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
330 : unsigned long timeout)
331 : {
332 6 : int ret;
333 :
334 6 : if (tty < tty2) {
335 0 : ret = __tty_ldisc_lock(tty, timeout);
336 0 : if (ret) {
337 0 : ret = __tty_ldisc_lock_nested(tty2, timeout);
338 0 : if (!ret)
339 0 : __tty_ldisc_unlock(tty);
340 0 : }
341 0 : } else {
342 : /* if this is possible, it has lots of implications */
343 6 : WARN_ON_ONCE(tty == tty2);
344 6 : if (tty2 && tty != tty2) {
345 0 : ret = __tty_ldisc_lock(tty2, timeout);
346 0 : if (ret) {
347 0 : ret = __tty_ldisc_lock_nested(tty, timeout);
348 0 : if (!ret)
349 0 : __tty_ldisc_unlock(tty2);
350 0 : }
351 0 : } else
352 6 : ret = __tty_ldisc_lock(tty, timeout);
353 : }
354 :
355 6 : if (!ret)
356 0 : return -EBUSY;
357 :
358 6 : set_bit(TTY_LDISC_HALTED, &tty->flags);
359 6 : if (tty2)
360 0 : set_bit(TTY_LDISC_HALTED, &tty2->flags);
361 6 : return 0;
362 6 : }
363 :
364 6 : static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
365 : {
366 6 : tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
367 6 : }
368 :
369 6 : static void tty_ldisc_unlock_pair(struct tty_struct *tty,
370 : struct tty_struct *tty2)
371 : {
372 6 : __tty_ldisc_unlock(tty);
373 6 : if (tty2)
374 0 : __tty_ldisc_unlock(tty2);
375 6 : }
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 : */
384 12 : void tty_ldisc_flush(struct tty_struct *tty)
385 : {
386 12 : struct tty_ldisc *ld = tty_ldisc_ref(tty);
387 :
388 12 : tty_buffer_flush(tty, ld);
389 12 : if (ld)
390 12 : tty_ldisc_deref(ld);
391 12 : }
392 : EXPORT_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 : */
407 0 : static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
408 : {
409 0 : down_write(&tty->termios_rwsem);
410 0 : tty->termios.c_line = disc;
411 0 : up_write(&tty->termios_rwsem);
412 :
413 0 : tty->disc_data = NULL;
414 0 : tty->receive_room = 0;
415 0 : }
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 : */
426 6 : static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
427 : {
428 6 : WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
429 6 : if (ld->ops->open) {
430 6 : int ret;
431 : /* BTM here locks versus a hangup event */
432 6 : ret = ld->ops->open(tty);
433 6 : if (ret)
434 0 : clear_bit(TTY_LDISC_OPEN, &tty->flags);
435 :
436 : tty_ldisc_debug(tty, "%p: opened\n", ld);
437 6 : return ret;
438 6 : }
439 0 : return 0;
440 6 : }
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 : */
449 6 : static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
450 : {
451 6 : lockdep_assert_held_write(&tty->ldisc_sem);
452 6 : WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
453 6 : clear_bit(TTY_LDISC_OPEN, &tty->flags);
454 6 : if (ld->ops->close)
455 6 : ld->ops->close(tty);
456 : tty_ldisc_debug(tty, "%p: closed\n", ld);
457 6 : }
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 : */
467 0 : static int tty_ldisc_failto(struct tty_struct *tty, int ld)
468 : {
469 0 : struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
470 0 : int r;
471 :
472 0 : lockdep_assert_held_write(&tty->ldisc_sem);
473 0 : if (IS_ERR(disc))
474 0 : return PTR_ERR(disc);
475 0 : tty->ldisc = disc;
476 0 : tty_set_termios_ldisc(tty, ld);
477 0 : r = tty_ldisc_open(tty, disc);
478 0 : if (r < 0)
479 0 : tty_ldisc_put(disc);
480 0 : return r;
481 0 : }
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 : */
491 0 : static 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 0 : if (tty_ldisc_failto(tty, old->ops->num) < 0) {
495 0 : const char *name = tty_name(tty);
496 :
497 0 : 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 0 : if (tty_ldisc_failto(tty, N_TTY) < 0 &&
504 0 : tty_ldisc_failto(tty, N_NULL) < 0)
505 0 : panic("Couldn't open N_NULL ldisc for %s.", name);
506 0 : }
507 0 : }
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 : */
519 0 : int tty_set_ldisc(struct tty_struct *tty, int disc)
520 : {
521 0 : int retval;
522 0 : struct tty_ldisc *old_ldisc, *new_ldisc;
523 :
524 0 : new_ldisc = tty_ldisc_get(tty, disc);
525 0 : if (IS_ERR(new_ldisc))
526 0 : return PTR_ERR(new_ldisc);
527 :
528 0 : tty_lock(tty);
529 0 : retval = tty_ldisc_lock(tty, 5 * HZ);
530 0 : if (retval)
531 0 : goto err;
532 :
533 0 : if (!tty->ldisc) {
534 0 : retval = -EIO;
535 0 : goto out;
536 : }
537 :
538 : /* Check the no-op case */
539 0 : if (tty->ldisc->ops->num == disc)
540 0 : goto out;
541 :
542 0 : if (test_bit(TTY_HUPPED, &tty->flags)) {
543 : /* We were raced by hangup */
544 0 : retval = -EIO;
545 0 : goto out;
546 : }
547 :
548 0 : if (tty->ops->ldisc_ok) {
549 0 : retval = tty->ops->ldisc_ok(tty, disc);
550 0 : if (retval)
551 0 : goto out;
552 0 : }
553 :
554 0 : old_ldisc = tty->ldisc;
555 :
556 : /* Shutdown the old discipline. */
557 0 : tty_ldisc_close(tty, old_ldisc);
558 :
559 : /* Now set up the new line discipline. */
560 0 : tty->ldisc = new_ldisc;
561 0 : tty_set_termios_ldisc(tty, disc);
562 :
563 0 : retval = tty_ldisc_open(tty, new_ldisc);
564 0 : if (retval < 0) {
565 : /* Back to the old one or N_TTY if we can't */
566 0 : tty_ldisc_put(new_ldisc);
567 0 : tty_ldisc_restore(tty, old_ldisc);
568 0 : }
569 :
570 0 : if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
571 0 : down_read(&tty->termios_rwsem);
572 0 : tty->ops->set_ldisc(tty);
573 0 : up_read(&tty->termios_rwsem);
574 0 : }
575 :
576 : /*
577 : * At this point we hold a reference to the new ldisc and a
578 : * reference to the old ldisc, or we hold two references to
579 : * the old ldisc (if it was restored as part of error cleanup
580 : * above). In either case, releasing a single reference from
581 : * the old ldisc is correct.
582 : */
583 0 : new_ldisc = old_ldisc;
584 : out:
585 0 : tty_ldisc_unlock(tty);
586 :
587 : /*
588 : * Restart the work queue in case no characters kick it off. Safe if
589 : * already running
590 : */
591 0 : tty_buffer_restart_work(tty->port);
592 : err:
593 0 : tty_ldisc_put(new_ldisc); /* drop the extra reference */
594 0 : tty_unlock(tty);
595 0 : return retval;
596 0 : }
597 : EXPORT_SYMBOL_GPL(tty_set_ldisc);
598 :
599 : /**
600 : * tty_ldisc_kill - teardown ldisc
601 : * @tty: tty being released
602 : *
603 : * Perform final close of the ldisc and reset @tty->ldisc
604 : */
605 6 : static void tty_ldisc_kill(struct tty_struct *tty)
606 : {
607 6 : lockdep_assert_held_write(&tty->ldisc_sem);
608 6 : if (!tty->ldisc)
609 0 : return;
610 : /*
611 : * Now kill off the ldisc
612 : */
613 6 : tty_ldisc_close(tty, tty->ldisc);
614 6 : tty_ldisc_put(tty->ldisc);
615 : /* Force an oops if we mess this up */
616 6 : tty->ldisc = NULL;
617 6 : }
618 :
619 : /**
620 : * tty_reset_termios - reset terminal state
621 : * @tty: tty to reset
622 : *
623 : * Restore a terminal to the driver default state.
624 : */
625 0 : static void tty_reset_termios(struct tty_struct *tty)
626 : {
627 0 : down_write(&tty->termios_rwsem);
628 0 : tty->termios = tty->driver->init_termios;
629 0 : tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
630 0 : tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
631 0 : up_write(&tty->termios_rwsem);
632 0 : }
633 :
634 :
635 : /**
636 : * tty_ldisc_reinit - reinitialise the tty ldisc
637 : * @tty: tty to reinit
638 : * @disc: line discipline to reinitialize
639 : *
640 : * Completely reinitialize the line discipline state, by closing the current
641 : * instance, if there is one, and opening a new instance. If an error occurs
642 : * opening the new non-%N_TTY instance, the instance is dropped and @tty->ldisc
643 : * reset to %NULL. The caller can then retry with %N_TTY instead.
644 : *
645 : * Returns: 0 if successful, otherwise error code < 0
646 : */
647 0 : int tty_ldisc_reinit(struct tty_struct *tty, int disc)
648 : {
649 0 : struct tty_ldisc *ld;
650 0 : int retval;
651 :
652 0 : lockdep_assert_held_write(&tty->ldisc_sem);
653 0 : ld = tty_ldisc_get(tty, disc);
654 0 : if (IS_ERR(ld)) {
655 0 : BUG_ON(disc == N_TTY);
656 0 : return PTR_ERR(ld);
657 : }
658 :
659 0 : if (tty->ldisc) {
660 0 : tty_ldisc_close(tty, tty->ldisc);
661 0 : tty_ldisc_put(tty->ldisc);
662 0 : }
663 :
664 : /* switch the line discipline */
665 0 : tty->ldisc = ld;
666 0 : tty_set_termios_ldisc(tty, disc);
667 0 : retval = tty_ldisc_open(tty, tty->ldisc);
668 0 : if (retval) {
669 0 : tty_ldisc_put(tty->ldisc);
670 0 : tty->ldisc = NULL;
671 0 : }
672 0 : return retval;
673 0 : }
674 :
675 : /**
676 : * tty_ldisc_hangup - hangup ldisc reset
677 : * @tty: tty being hung up
678 : * @reinit: whether to re-initialise the tty
679 : *
680 : * Some tty devices reset their termios when they receive a hangup event. In
681 : * that situation we must also switch back to %N_TTY properly before we reset
682 : * the termios data.
683 : *
684 : * Locking: We can take the ldisc mutex as the rest of the code is careful to
685 : * allow for this.
686 : *
687 : * In the pty pair case this occurs in the close() path of the tty itself so we
688 : * must be careful about locking rules.
689 : */
690 0 : void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
691 : {
692 0 : struct tty_ldisc *ld;
693 :
694 : tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
695 :
696 0 : ld = tty_ldisc_ref(tty);
697 0 : if (ld != NULL) {
698 0 : if (ld->ops->flush_buffer)
699 0 : ld->ops->flush_buffer(tty);
700 0 : tty_driver_flush_buffer(tty);
701 0 : if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
702 0 : ld->ops->write_wakeup)
703 0 : ld->ops->write_wakeup(tty);
704 0 : if (ld->ops->hangup)
705 0 : ld->ops->hangup(tty);
706 0 : tty_ldisc_deref(ld);
707 0 : }
708 :
709 0 : wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
710 0 : wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
711 :
712 : /*
713 : * Shutdown the current line discipline, and reset it to
714 : * N_TTY if need be.
715 : *
716 : * Avoid racing set_ldisc or tty_ldisc_release
717 : */
718 0 : tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
719 :
720 0 : if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
721 0 : tty_reset_termios(tty);
722 :
723 0 : if (tty->ldisc) {
724 0 : if (reinit) {
725 0 : if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
726 0 : tty_ldisc_reinit(tty, N_TTY) < 0)
727 0 : WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
728 0 : } else
729 0 : tty_ldisc_kill(tty);
730 0 : }
731 0 : tty_ldisc_unlock(tty);
732 0 : }
733 :
734 : /**
735 : * tty_ldisc_setup - open line discipline
736 : * @tty: tty being shut down
737 : * @o_tty: pair tty for pty/tty pairs
738 : *
739 : * Called during the initial open of a tty/pty pair in order to set up the line
740 : * disciplines and bind them to the @tty. This has no locking issues as the
741 : * device isn't yet active.
742 : */
743 6 : int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
744 : {
745 6 : int retval = tty_ldisc_open(tty, tty->ldisc);
746 :
747 6 : if (retval)
748 0 : return retval;
749 :
750 6 : if (o_tty) {
751 : /*
752 : * Called without o_tty->ldisc_sem held, as o_tty has been
753 : * just allocated and no one has a reference to it.
754 : */
755 0 : retval = tty_ldisc_open(o_tty, o_tty->ldisc);
756 0 : if (retval) {
757 0 : tty_ldisc_close(tty, tty->ldisc);
758 0 : return retval;
759 : }
760 0 : }
761 6 : return 0;
762 6 : }
763 :
764 : /**
765 : * tty_ldisc_release - release line discipline
766 : * @tty: tty being shut down (or one end of pty pair)
767 : *
768 : * Called during the final close of a tty or a pty pair in order to shut down
769 : * the line discpline layer. On exit, each tty's ldisc is %NULL.
770 : */
771 6 : void tty_ldisc_release(struct tty_struct *tty)
772 : {
773 6 : struct tty_struct *o_tty = tty->link;
774 :
775 : /*
776 : * Shutdown this line discipline. As this is the final close,
777 : * it does not race with the set_ldisc code path.
778 : */
779 :
780 6 : tty_ldisc_lock_pair(tty, o_tty);
781 6 : tty_ldisc_kill(tty);
782 6 : if (o_tty)
783 0 : tty_ldisc_kill(o_tty);
784 6 : tty_ldisc_unlock_pair(tty, o_tty);
785 :
786 : /*
787 : * And the memory resources remaining (buffers, termios) will be
788 : * disposed of when the kref hits zero
789 : */
790 :
791 : tty_ldisc_debug(tty, "released\n");
792 6 : }
793 :
794 : /**
795 : * tty_ldisc_init - ldisc setup for new tty
796 : * @tty: tty being allocated
797 : *
798 : * Set up the line discipline objects for a newly allocated tty. Note that the
799 : * tty structure is not completely set up when this call is made.
800 : */
801 6 : int tty_ldisc_init(struct tty_struct *tty)
802 : {
803 6 : struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
804 :
805 6 : if (IS_ERR(ld))
806 0 : return PTR_ERR(ld);
807 6 : tty->ldisc = ld;
808 6 : return 0;
809 6 : }
810 :
811 : /**
812 : * tty_ldisc_deinit - ldisc cleanup for new tty
813 : * @tty: tty that was allocated recently
814 : *
815 : * The tty structure must not be completely set up (tty_ldisc_setup()) when
816 : * this call is made.
817 : */
818 6 : void tty_ldisc_deinit(struct tty_struct *tty)
819 : {
820 : /* no ldisc_sem, tty is being destroyed */
821 6 : if (tty->ldisc)
822 0 : tty_ldisc_put(tty->ldisc);
823 6 : tty->ldisc = NULL;
824 6 : }
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