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 3 : int tty_register_ldisc(struct tty_ldisc_ops *new_ldisc)
59 : {
60 : unsigned long flags;
61 :
62 3 : if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS)
63 : return -EINVAL;
64 :
65 3 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
66 3 : tty_ldiscs[new_ldisc->num] = new_ldisc;
67 6 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
68 :
69 3 : return 0;
70 : }
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 : 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 0 : static struct tty_ldisc_ops *get_ldops(int disc)
94 : {
95 : unsigned long flags;
96 : struct tty_ldisc_ops *ldops, *ret;
97 :
98 0 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
99 0 : ret = ERR_PTR(-EINVAL);
100 0 : ldops = tty_ldiscs[disc];
101 0 : if (ldops) {
102 0 : ret = ERR_PTR(-EAGAIN);
103 0 : if (try_module_get(ldops->owner))
104 0 : ret = ldops;
105 : }
106 0 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107 0 : return ret;
108 : }
109 :
110 : static void put_ldops(struct tty_ldisc_ops *ldops)
111 : {
112 : unsigned long flags;
113 :
114 0 : raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115 0 : module_put(ldops->owner);
116 0 : raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
117 : }
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 0 : static 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 0 : 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 0 : ldops = get_ldops(disc);
152 0 : if (IS_ERR(ldops)) {
153 0 : if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
154 : 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 : 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 0 : ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
166 0 : ld->ops = ldops;
167 0 : ld->tty = tty;
168 :
169 0 : 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 : */
178 0 : static void tty_ldisc_put(struct tty_ldisc *ld)
179 : {
180 0 : if (WARN_ON_ONCE(!ld))
181 : return;
182 :
183 0 : put_ldops(ld->ops);
184 0 : kfree(ld);
185 : }
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 : struct tty_ldisc_ops *ldops;
206 :
207 0 : ldops = get_ldops(i);
208 0 : if (IS_ERR(ldops))
209 : 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 : }
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 0 : struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
240 : {
241 : struct tty_ldisc *ld;
242 :
243 0 : ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
244 0 : ld = tty->ldisc;
245 0 : if (!ld)
246 0 : ldsem_up_read(&tty->ldisc_sem);
247 0 : return ld;
248 : }
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 0 : struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
260 : {
261 0 : struct tty_ldisc *ld = NULL;
262 :
263 0 : if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
264 0 : ld = tty->ldisc;
265 0 : if (!ld)
266 0 : ldsem_up_read(&tty->ldisc_sem);
267 : }
268 0 : return ld;
269 : }
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 0 : void tty_ldisc_deref(struct tty_ldisc *ld)
280 : {
281 0 : ldsem_up_read(&ld->tty->ldisc_sem);
282 0 : }
283 : EXPORT_SYMBOL_GPL(tty_ldisc_deref);
284 :
285 :
286 : static inline int
287 : __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
288 : {
289 0 : return ldsem_down_write(&tty->ldisc_sem, timeout);
290 : }
291 :
292 : static inline int
293 : __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
294 : {
295 0 : return ldsem_down_write_nested(&tty->ldisc_sem,
296 : LDISC_SEM_OTHER, timeout);
297 : }
298 :
299 : static inline void __tty_ldisc_unlock(struct tty_struct *tty)
300 : {
301 0 : ldsem_up_write(&tty->ldisc_sem);
302 : }
303 :
304 0 : int 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 0 : set_bit(TTY_LDISC_CHANGING, &tty->flags);
310 0 : wake_up_interruptible_all(&tty->read_wait);
311 0 : wake_up_interruptible_all(&tty->write_wait);
312 :
313 0 : ret = __tty_ldisc_lock(tty, timeout);
314 0 : if (!ret)
315 : return -EBUSY;
316 0 : set_bit(TTY_LDISC_HALTED, &tty->flags);
317 0 : return 0;
318 : }
319 :
320 0 : void tty_ldisc_unlock(struct tty_struct *tty)
321 : {
322 0 : clear_bit(TTY_LDISC_HALTED, &tty->flags);
323 : /* Can be cleared here - ldisc_unlock will wake up writers firstly */
324 0 : clear_bit(TTY_LDISC_CHANGING, &tty->flags);
325 0 : __tty_ldisc_unlock(tty);
326 0 : }
327 :
328 : static int
329 0 : tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
330 : unsigned long timeout)
331 : {
332 : int ret;
333 :
334 0 : 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 : __tty_ldisc_unlock(tty);
340 : }
341 : } else {
342 : /* if this is possible, it has lots of implications */
343 0 : WARN_ON_ONCE(tty == tty2);
344 0 : 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 : __tty_ldisc_unlock(tty2);
350 : }
351 : } else
352 0 : ret = __tty_ldisc_lock(tty, timeout);
353 : }
354 :
355 0 : if (!ret)
356 : return -EBUSY;
357 :
358 0 : set_bit(TTY_LDISC_HALTED, &tty->flags);
359 0 : if (tty2)
360 0 : set_bit(TTY_LDISC_HALTED, &tty2->flags);
361 : return 0;
362 : }
363 :
364 : static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
365 : {
366 0 : tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
367 : }
368 :
369 : static void tty_ldisc_unlock_pair(struct tty_struct *tty,
370 : struct tty_struct *tty2)
371 : {
372 0 : __tty_ldisc_unlock(tty);
373 0 : 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 : */
384 0 : void tty_ldisc_flush(struct tty_struct *tty)
385 : {
386 0 : struct tty_ldisc *ld = tty_ldisc_ref(tty);
387 :
388 0 : tty_buffer_flush(tty, ld);
389 0 : if (ld)
390 : tty_ldisc_deref(ld);
391 0 : }
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 : 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 : }
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 0 : static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
427 : {
428 0 : WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
429 0 : if (ld->ops->open) {
430 : int ret;
431 : /* BTM here locks versus a hangup event */
432 0 : ret = ld->ops->open(tty);
433 0 : if (ret)
434 0 : 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 : */
449 0 : static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
450 : {
451 : lockdep_assert_held_write(&tty->ldisc_sem);
452 0 : WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
453 0 : clear_bit(TTY_LDISC_OPEN, &tty->flags);
454 0 : if (ld->ops->close)
455 0 : ld->ops->close(tty);
456 : tty_ldisc_debug(tty, "%p: closed\n", ld);
457 0 : }
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 : int r;
471 :
472 : 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 : 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 : */
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 : }
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 : int retval;
522 : 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 : goto err;
532 :
533 0 : if (!tty->ldisc) {
534 : retval = -EIO;
535 : goto out;
536 : }
537 :
538 : /* Check the no-op case */
539 0 : if (tty->ldisc->ops->num == disc)
540 : goto out;
541 :
542 0 : if (test_bit(TTY_HUPPED, &tty->flags)) {
543 : /* We were raced by hangup */
544 : retval = -EIO;
545 : goto out;
546 : }
547 :
548 0 : old_ldisc = tty->ldisc;
549 :
550 : /* Shutdown the old discipline. */
551 0 : tty_ldisc_close(tty, old_ldisc);
552 :
553 : /* Now set up the new line discipline. */
554 0 : tty->ldisc = new_ldisc;
555 0 : tty_set_termios_ldisc(tty, disc);
556 :
557 0 : retval = tty_ldisc_open(tty, new_ldisc);
558 0 : if (retval < 0) {
559 : /* Back to the old one or N_TTY if we can't */
560 0 : tty_ldisc_put(new_ldisc);
561 0 : tty_ldisc_restore(tty, old_ldisc);
562 : }
563 :
564 0 : if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
565 0 : down_read(&tty->termios_rwsem);
566 0 : tty->ops->set_ldisc(tty);
567 0 : 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;
578 : out:
579 0 : 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 0 : tty_buffer_restart_work(tty->port);
586 : err:
587 0 : tty_ldisc_put(new_ldisc); /* drop the extra reference */
588 0 : tty_unlock(tty);
589 0 : return retval;
590 : }
591 : EXPORT_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 : */
599 0 : static void tty_ldisc_kill(struct tty_struct *tty)
600 : {
601 : lockdep_assert_held_write(&tty->ldisc_sem);
602 0 : if (!tty->ldisc)
603 : return;
604 : /*
605 : * Now kill off the ldisc
606 : */
607 0 : tty_ldisc_close(tty, tty->ldisc);
608 0 : tty_ldisc_put(tty->ldisc);
609 : /* Force an oops if we mess this up */
610 0 : 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 : */
619 0 : static void tty_reset_termios(struct tty_struct *tty)
620 : {
621 0 : down_write(&tty->termios_rwsem);
622 0 : tty->termios = tty->driver->init_termios;
623 0 : tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
624 0 : tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
625 0 : up_write(&tty->termios_rwsem);
626 0 : }
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 : */
641 0 : int 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 0 : ld = tty_ldisc_get(tty, disc);
648 0 : if (IS_ERR(ld)) {
649 0 : BUG_ON(disc == N_TTY);
650 0 : return PTR_ERR(ld);
651 : }
652 :
653 0 : if (tty->ldisc) {
654 0 : tty_ldisc_close(tty, tty->ldisc);
655 0 : tty_ldisc_put(tty->ldisc);
656 : }
657 :
658 : /* switch the line discipline */
659 0 : tty->ldisc = ld;
660 0 : tty_set_termios_ldisc(tty, disc);
661 0 : retval = tty_ldisc_open(tty, tty->ldisc);
662 0 : if (retval) {
663 0 : tty_ldisc_put(tty->ldisc);
664 0 : 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 : */
684 0 : void 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 0 : ld = tty_ldisc_ref(tty);
691 0 : if (ld != NULL) {
692 0 : if (ld->ops->flush_buffer)
693 0 : ld->ops->flush_buffer(tty);
694 0 : tty_driver_flush_buffer(tty);
695 0 : if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
696 0 : ld->ops->write_wakeup)
697 0 : ld->ops->write_wakeup(tty);
698 0 : if (ld->ops->hangup)
699 0 : ld->ops->hangup(tty);
700 : tty_ldisc_deref(ld);
701 : }
702 :
703 0 : wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
704 0 : 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 0 : tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
713 :
714 0 : if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
715 0 : tty_reset_termios(tty);
716 :
717 0 : if (tty->ldisc) {
718 0 : if (reinit) {
719 0 : if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
720 0 : tty_ldisc_reinit(tty, N_TTY) < 0)
721 0 : WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
722 : } else
723 0 : tty_ldisc_kill(tty);
724 : }
725 0 : tty_ldisc_unlock(tty);
726 0 : }
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 : */
737 0 : int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
738 : {
739 0 : int retval = tty_ldisc_open(tty, tty->ldisc);
740 :
741 0 : if (retval)
742 : return retval;
743 :
744 0 : 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 0 : retval = tty_ldisc_open(o_tty, o_tty->ldisc);
750 0 : if (retval) {
751 0 : tty_ldisc_close(tty, tty->ldisc);
752 0 : 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 : */
765 0 : void tty_ldisc_release(struct tty_struct *tty)
766 : {
767 0 : 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 0 : tty_ldisc_lock_pair(tty, o_tty);
775 0 : tty_ldisc_kill(tty);
776 0 : if (o_tty)
777 0 : tty_ldisc_kill(o_tty);
778 0 : 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 0 : }
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 : */
795 0 : int tty_ldisc_init(struct tty_struct *tty)
796 : {
797 0 : struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
798 :
799 0 : if (IS_ERR(ld))
800 0 : return PTR_ERR(ld);
801 0 : tty->ldisc = ld;
802 0 : 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 : */
812 0 : void tty_ldisc_deinit(struct tty_struct *tty)
813 : {
814 : /* no ldisc_sem, tty is being destroyed */
815 0 : if (tty->ldisc)
816 0 : tty_ldisc_put(tty->ldisc);
817 0 : tty->ldisc = NULL;
818 0 : }
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