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