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1// SPDX-License-Identifier: GPL-2.0
2#include <linux/types.h>
3#include <linux/errno.h>
4#include <linux/kmod.h>
5#include <linux/sched.h>
6#include <linux/interrupt.h>
7#include <linux/tty.h>
8#include <linux/tty_driver.h>
9#include <linux/file.h>
10#include <linux/mm.h>
11#include <linux/string.h>
12#include <linux/slab.h>
13#include <linux/poll.h>
14#include <linux/proc_fs.h>
15#include <linux/module.h>
16#include <linux/device.h>
17#include <linux/wait.h>
18#include <linux/bitops.h>
19#include <linux/seq_file.h>
20#include <linux/uaccess.h>
21#include <linux/ratelimit.h>
22#include "tty.h"
23
24#undef LDISC_DEBUG_HANGUP
25
26#ifdef LDISC_DEBUG_HANGUP
27#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
28#else
29#define tty_ldisc_debug(tty, f, args...)
30#endif
31
32/* lockdep nested classes for tty->ldisc_sem */
33enum {
34 LDISC_SEM_NORMAL,
35 LDISC_SEM_OTHER,
36};
37
38
39/*
40 * This guards the refcounted line discipline lists. The lock
41 * must be taken with irqs off because there are hangup path
42 * callers who will do ldisc lookups and cannot sleep.
43 */
44
45static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
46/* Line disc dispatch table */
47static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
48
49/**
50 * tty_register_ldisc - install a line discipline
51 * @new_ldisc: pointer to the ldisc object
52 *
53 * Installs a new line discipline into the kernel. The discipline is set up as
54 * unreferenced and then made available to the kernel from this point onwards.
55 *
56 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
57 */
58int tty_register_ldisc(struct tty_ldisc_ops *new_ldisc)
59{
60 unsigned long flags;
61
62 if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS)
63 return -EINVAL;
64
65 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
66 tty_ldiscs[new_ldisc->num] = new_ldisc;
67 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
68
69 return 0;
70}
71EXPORT_SYMBOL(tty_register_ldisc);
72
73/**
74 * tty_unregister_ldisc - unload a line discipline
75 * @ldisc: ldisc number
76 *
77 * Remove a line discipline from the kernel providing it is not currently in
78 * use.
79 *
80 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
81 */
82
83void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc)
84{
85 unsigned long flags;
86
87 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
88 tty_ldiscs[ldisc->num] = NULL;
89 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
90}
91EXPORT_SYMBOL(tty_unregister_ldisc);
92
93static struct tty_ldisc_ops *get_ldops(int disc)
94{
95 unsigned long flags;
96 struct tty_ldisc_ops *ldops, *ret;
97
98 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
99 ret = ERR_PTR(-EINVAL);
100 ldops = tty_ldiscs[disc];
101 if (ldops) {
102 ret = ERR_PTR(-EAGAIN);
103 if (try_module_get(ldops->owner))
104 ret = ldops;
105 }
106 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107 return ret;
108}
109
110static void put_ldops(struct tty_ldisc_ops *ldops)
111{
112 unsigned long flags;
113
114 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115 module_put(ldops->owner);
116 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
117}
118
119int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
120
121/**
122 * tty_ldisc_get - take a reference to an ldisc
123 * @tty: tty device
124 * @disc: ldisc number
125 *
126 * Takes a reference to a line discipline. Deals with refcounts and module
127 * locking counts. If the discipline is not available, its module loaded, if
128 * possible.
129 *
130 * Returns:
131 * * -%EINVAL if the discipline index is not [%N_TTY .. %NR_LDISCS] or if the
132 * discipline is not registered
133 * * -%EAGAIN if request_module() failed to load or register the discipline
134 * * -%ENOMEM if allocation failure
135 * * Otherwise, returns a pointer to the discipline and bumps the ref count
136 *
137 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
138 */
139static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
140{
141 struct tty_ldisc *ld;
142 struct tty_ldisc_ops *ldops;
143
144 if (disc < N_TTY || disc >= NR_LDISCS)
145 return ERR_PTR(-EINVAL);
146
147 /*
148 * Get the ldisc ops - we may need to request them to be loaded
149 * dynamically and try again.
150 */
151 ldops = get_ldops(disc);
152 if (IS_ERR(ldops)) {
153 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
154 return ERR_PTR(-EPERM);
155 request_module("tty-ldisc-%d", disc);
156 ldops = get_ldops(disc);
157 if (IS_ERR(ldops))
158 return ERR_CAST(ldops);
159 }
160
161 /*
162 * There is no way to handle allocation failure of only 16 bytes.
163 * Let's simplify error handling and save more memory.
164 */
165 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
166 ld->ops = ldops;
167 ld->tty = tty;
168
169 return ld;
170}
171
172/**
173 * tty_ldisc_put - release the ldisc
174 * @ld: lisdsc to release
175 *
176 * Complement of tty_ldisc_get().
177 */
178static void tty_ldisc_put(struct tty_ldisc *ld)
179{
180 if (WARN_ON_ONCE(!ld))
181 return;
182
183 put_ldops(ld->ops);
184 kfree(ld);
185}
186
187static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
188{
189 return (*pos < NR_LDISCS) ? pos : NULL;
190}
191
192static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
193{
194 (*pos)++;
195 return (*pos < NR_LDISCS) ? pos : NULL;
196}
197
198static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
199{
200}
201
202static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
203{
204 int i = *(loff_t *)v;
205 struct tty_ldisc_ops *ldops;
206
207 ldops = get_ldops(i);
208 if (IS_ERR(ldops))
209 return 0;
210 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
211 put_ldops(ldops);
212 return 0;
213}
214
215const struct seq_operations tty_ldiscs_seq_ops = {
216 .start = tty_ldiscs_seq_start,
217 .next = tty_ldiscs_seq_next,
218 .stop = tty_ldiscs_seq_stop,
219 .show = tty_ldiscs_seq_show,
220};
221
222/**
223 * tty_ldisc_ref_wait - wait for the tty ldisc
224 * @tty: tty device
225 *
226 * Dereference the line discipline for the terminal and take a reference to it.
227 * If the line discipline is in flux then wait patiently until it changes.
228 *
229 * Returns: %NULL if the tty has been hungup and not re-opened with a new file
230 * descriptor, otherwise valid ldisc reference
231 *
232 * Note 1: Must not be called from an IRQ/timer context. The caller must also
233 * be careful not to hold other locks that will deadlock against a discipline
234 * change, such as an existing ldisc reference (which we check for).
235 *
236 * Note 2: a file_operations routine (read/poll/write) should use this function
237 * to wait for any ldisc lifetime events to finish.
238 */
239struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
240{
241 struct tty_ldisc *ld;
242
243 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
244 ld = tty->ldisc;
245 if (!ld)
246 ldsem_up_read(&tty->ldisc_sem);
247 return ld;
248}
249EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
250
251/**
252 * tty_ldisc_ref - get the tty ldisc
253 * @tty: tty device
254 *
255 * Dereference the line discipline for the terminal and take a reference to it.
256 * If the line discipline is in flux then return %NULL. Can be called from IRQ
257 * and timer functions.
258 */
259struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
260{
261 struct tty_ldisc *ld = NULL;
262
263 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
264 ld = tty->ldisc;
265 if (!ld)
266 ldsem_up_read(&tty->ldisc_sem);
267 }
268 return ld;
269}
270EXPORT_SYMBOL_GPL(tty_ldisc_ref);
271
272/**
273 * tty_ldisc_deref - free a tty ldisc reference
274 * @ld: reference to free up
275 *
276 * Undoes the effect of tty_ldisc_ref() or tty_ldisc_ref_wait(). May be called
277 * in IRQ context.
278 */
279void tty_ldisc_deref(struct tty_ldisc *ld)
280{
281 ldsem_up_read(&ld->tty->ldisc_sem);
282}
283EXPORT_SYMBOL_GPL(tty_ldisc_deref);
284
285
286static inline int
287__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
288{
289 return ldsem_down_write(&tty->ldisc_sem, timeout);
290}
291
292static inline int
293__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
294{
295 return ldsem_down_write_nested(&tty->ldisc_sem,
296 LDISC_SEM_OTHER, timeout);
297}
298
299static inline void __tty_ldisc_unlock(struct tty_struct *tty)
300{
301 ldsem_up_write(&tty->ldisc_sem);
302}
303
304int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
305{
306 int ret;
307
308 /* Kindly asking blocked readers to release the read side */
309 set_bit(TTY_LDISC_CHANGING, &tty->flags);
310 wake_up_interruptible_all(&tty->read_wait);
311 wake_up_interruptible_all(&tty->write_wait);
312
313 ret = __tty_ldisc_lock(tty, timeout);
314 if (!ret)
315 return -EBUSY;
316 set_bit(TTY_LDISC_HALTED, &tty->flags);
317 return 0;
318}
319
320void tty_ldisc_unlock(struct tty_struct *tty)
321{
322 clear_bit(TTY_LDISC_HALTED, &tty->flags);
323 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
324 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
325 __tty_ldisc_unlock(tty);
326}
327
328static int
329tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
330 unsigned long timeout)
331{
332 int ret;
333
334 if (tty < tty2) {
335 ret = __tty_ldisc_lock(tty, timeout);
336 if (ret) {
337 ret = __tty_ldisc_lock_nested(tty2, timeout);
338 if (!ret)
339 __tty_ldisc_unlock(tty);
340 }
341 } else {
342 /* if this is possible, it has lots of implications */
343 WARN_ON_ONCE(tty == tty2);
344 if (tty2 && tty != tty2) {
345 ret = __tty_ldisc_lock(tty2, timeout);
346 if (ret) {
347 ret = __tty_ldisc_lock_nested(tty, timeout);
348 if (!ret)
349 __tty_ldisc_unlock(tty2);
350 }
351 } else
352 ret = __tty_ldisc_lock(tty, timeout);
353 }
354
355 if (!ret)
356 return -EBUSY;
357
358 set_bit(TTY_LDISC_HALTED, &tty->flags);
359 if (tty2)
360 set_bit(TTY_LDISC_HALTED, &tty2->flags);
361 return 0;
362}
363
364static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
365{
366 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
367}
368
369static void tty_ldisc_unlock_pair(struct tty_struct *tty,
370 struct tty_struct *tty2)
371{
372 __tty_ldisc_unlock(tty);
373 if (tty2)
374 __tty_ldisc_unlock(tty2);
375}
376
377/**
378 * tty_ldisc_flush - flush line discipline queue
379 * @tty: tty to flush ldisc for
380 *
381 * Flush the line discipline queue (if any) and the tty flip buffers for this
382 * @tty.
383 */
384void tty_ldisc_flush(struct tty_struct *tty)
385{
386 struct tty_ldisc *ld = tty_ldisc_ref(tty);
387
388 tty_buffer_flush(tty, ld);
389 if (ld)
390 tty_ldisc_deref(ld);
391}
392EXPORT_SYMBOL_GPL(tty_ldisc_flush);
393
394/**
395 * tty_set_termios_ldisc - set ldisc field
396 * @tty: tty structure
397 * @disc: line discipline number
398 *
399 * This is probably overkill for real world processors but they are not on hot
400 * paths so a little discipline won't do any harm.
401 *
402 * The line discipline-related tty_struct fields are reset to prevent the ldisc
403 * driver from re-using stale information for the new ldisc instance.
404 *
405 * Locking: takes termios_rwsem
406 */
407static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
408{
409 down_write(&tty->termios_rwsem);
410 tty->termios.c_line = disc;
411 up_write(&tty->termios_rwsem);
412
413 tty->disc_data = NULL;
414 tty->receive_room = 0;
415}
416
417/**
418 * tty_ldisc_open - open a line discipline
419 * @tty: tty we are opening the ldisc on
420 * @ld: discipline to open
421 *
422 * A helper opening method. Also a convenient debugging and check point.
423 *
424 * Locking: always called with BTM already held.
425 */
426static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
427{
428 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
429 if (ld->ops->open) {
430 int ret;
431 /* BTM here locks versus a hangup event */
432 ret = ld->ops->open(tty);
433 if (ret)
434 clear_bit(TTY_LDISC_OPEN, &tty->flags);
435
436 tty_ldisc_debug(tty, "%p: opened\n", ld);
437 return ret;
438 }
439 return 0;
440}
441
442/**
443 * tty_ldisc_close - close a line discipline
444 * @tty: tty we are opening the ldisc on
445 * @ld: discipline to close
446 *
447 * A helper close method. Also a convenient debugging and check point.
448 */
449static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
450{
451 lockdep_assert_held_write(&tty->ldisc_sem);
452 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
453 clear_bit(TTY_LDISC_OPEN, &tty->flags);
454 if (ld->ops->close)
455 ld->ops->close(tty);
456 tty_ldisc_debug(tty, "%p: closed\n", ld);
457}
458
459/**
460 * tty_ldisc_failto - helper for ldisc failback
461 * @tty: tty to open the ldisc on
462 * @ld: ldisc we are trying to fail back to
463 *
464 * Helper to try and recover a tty when switching back to the old ldisc fails
465 * and we need something attached.
466 */
467static int tty_ldisc_failto(struct tty_struct *tty, int ld)
468{
469 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
470 int r;
471
472 lockdep_assert_held_write(&tty->ldisc_sem);
473 if (IS_ERR(disc))
474 return PTR_ERR(disc);
475 tty->ldisc = disc;
476 tty_set_termios_ldisc(tty, ld);
477 r = tty_ldisc_open(tty, disc);
478 if (r < 0)
479 tty_ldisc_put(disc);
480 return r;
481}
482
483/**
484 * tty_ldisc_restore - helper for tty ldisc change
485 * @tty: tty to recover
486 * @old: previous ldisc
487 *
488 * Restore the previous line discipline or %N_TTY when a line discipline change
489 * fails due to an open error
490 */
491static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
492{
493 /* There is an outstanding reference here so this is safe */
494 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
495 const char *name = tty_name(tty);
496
497 pr_warn("Falling back ldisc for %s.\n", name);
498 /*
499 * The traditional behaviour is to fall back to N_TTY, we
500 * want to avoid falling back to N_NULL unless we have no
501 * choice to avoid the risk of breaking anything
502 */
503 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
504 tty_ldisc_failto(tty, N_NULL) < 0)
505 panic("Couldn't open N_NULL ldisc for %s.", name);
506 }
507}
508
509/**
510 * tty_set_ldisc - set line discipline
511 * @tty: the terminal to set
512 * @disc: the line discipline number
513 *
514 * Set the discipline of a tty line. Must be called from a process context. The
515 * ldisc change logic has to protect itself against any overlapping ldisc
516 * change (including on the other end of pty pairs), the close of one side of a
517 * tty/pty pair, and eventually hangup.
518 */
519int tty_set_ldisc(struct tty_struct *tty, int disc)
520{
521 int retval;
522 struct tty_ldisc *old_ldisc, *new_ldisc;
523
524 new_ldisc = tty_ldisc_get(tty, disc);
525 if (IS_ERR(new_ldisc))
526 return PTR_ERR(new_ldisc);
527
528 tty_lock(tty);
529 retval = tty_ldisc_lock(tty, 5 * HZ);
530 if (retval)
531 goto err;
532
533 if (!tty->ldisc) {
534 retval = -EIO;
535 goto out;
536 }
537
538 /* Check the no-op case */
539 if (tty->ldisc->ops->num == disc)
540 goto out;
541
542 if (test_bit(TTY_HUPPED, &tty->flags)) {
543 /* We were raced by hangup */
544 retval = -EIO;
545 goto out;
546 }
547
548 old_ldisc = tty->ldisc;
549
550 /* Shutdown the old discipline. */
551 tty_ldisc_close(tty, old_ldisc);
552
553 /* Now set up the new line discipline. */
554 tty->ldisc = new_ldisc;
555 tty_set_termios_ldisc(tty, disc);
556
557 retval = tty_ldisc_open(tty, new_ldisc);
558 if (retval < 0) {
559 /* Back to the old one or N_TTY if we can't */
560 tty_ldisc_put(new_ldisc);
561 tty_ldisc_restore(tty, old_ldisc);
562 }
563
564 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
565 down_read(&tty->termios_rwsem);
566 tty->ops->set_ldisc(tty);
567 up_read(&tty->termios_rwsem);
568 }
569
570 /*
571 * At this point we hold a reference to the new ldisc and a
572 * reference to the old ldisc, or we hold two references to
573 * the old ldisc (if it was restored as part of error cleanup
574 * above). In either case, releasing a single reference from
575 * the old ldisc is correct.
576 */
577 new_ldisc = old_ldisc;
578out:
579 tty_ldisc_unlock(tty);
580
581 /*
582 * Restart the work queue in case no characters kick it off. Safe if
583 * already running
584 */
585 tty_buffer_restart_work(tty->port);
586err:
587 tty_ldisc_put(new_ldisc); /* drop the extra reference */
588 tty_unlock(tty);
589 return retval;
590}
591EXPORT_SYMBOL_GPL(tty_set_ldisc);
592
593/**
594 * tty_ldisc_kill - teardown ldisc
595 * @tty: tty being released
596 *
597 * Perform final close of the ldisc and reset @tty->ldisc
598 */
599static void tty_ldisc_kill(struct tty_struct *tty)
600{
601 lockdep_assert_held_write(&tty->ldisc_sem);
602 if (!tty->ldisc)
603 return;
604 /*
605 * Now kill off the ldisc
606 */
607 tty_ldisc_close(tty, tty->ldisc);
608 tty_ldisc_put(tty->ldisc);
609 /* Force an oops if we mess this up */
610 tty->ldisc = NULL;
611}
612
613/**
614 * tty_reset_termios - reset terminal state
615 * @tty: tty to reset
616 *
617 * Restore a terminal to the driver default state.
618 */
619static void tty_reset_termios(struct tty_struct *tty)
620{
621 down_write(&tty->termios_rwsem);
622 tty->termios = tty->driver->init_termios;
623 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
624 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
625 up_write(&tty->termios_rwsem);
626}
627
628
629/**
630 * tty_ldisc_reinit - reinitialise the tty ldisc
631 * @tty: tty to reinit
632 * @disc: line discipline to reinitialize
633 *
634 * Completely reinitialize the line discipline state, by closing the current
635 * instance, if there is one, and opening a new instance. If an error occurs
636 * opening the new non-%N_TTY instance, the instance is dropped and @tty->ldisc
637 * reset to %NULL. The caller can then retry with %N_TTY instead.
638 *
639 * Returns: 0 if successful, otherwise error code < 0
640 */
641int tty_ldisc_reinit(struct tty_struct *tty, int disc)
642{
643 struct tty_ldisc *ld;
644 int retval;
645
646 lockdep_assert_held_write(&tty->ldisc_sem);
647 ld = tty_ldisc_get(tty, disc);
648 if (IS_ERR(ld)) {
649 BUG_ON(disc == N_TTY);
650 return PTR_ERR(ld);
651 }
652
653 if (tty->ldisc) {
654 tty_ldisc_close(tty, tty->ldisc);
655 tty_ldisc_put(tty->ldisc);
656 }
657
658 /* switch the line discipline */
659 tty->ldisc = ld;
660 tty_set_termios_ldisc(tty, disc);
661 retval = tty_ldisc_open(tty, tty->ldisc);
662 if (retval) {
663 tty_ldisc_put(tty->ldisc);
664 tty->ldisc = NULL;
665 }
666 return retval;
667}
668
669/**
670 * tty_ldisc_hangup - hangup ldisc reset
671 * @tty: tty being hung up
672 * @reinit: whether to re-initialise the tty
673 *
674 * Some tty devices reset their termios when they receive a hangup event. In
675 * that situation we must also switch back to %N_TTY properly before we reset
676 * the termios data.
677 *
678 * Locking: We can take the ldisc mutex as the rest of the code is careful to
679 * allow for this.
680 *
681 * In the pty pair case this occurs in the close() path of the tty itself so we
682 * must be careful about locking rules.
683 */
684void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
685{
686 struct tty_ldisc *ld;
687
688 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
689
690 ld = tty_ldisc_ref(tty);
691 if (ld != NULL) {
692 if (ld->ops->flush_buffer)
693 ld->ops->flush_buffer(tty);
694 tty_driver_flush_buffer(tty);
695 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
696 ld->ops->write_wakeup)
697 ld->ops->write_wakeup(tty);
698 if (ld->ops->hangup)
699 ld->ops->hangup(tty);
700 tty_ldisc_deref(ld);
701 }
702
703 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
704 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
705
706 /*
707 * Shutdown the current line discipline, and reset it to
708 * N_TTY if need be.
709 *
710 * Avoid racing set_ldisc or tty_ldisc_release
711 */
712 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
713
714 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
715 tty_reset_termios(tty);
716
717 if (tty->ldisc) {
718 if (reinit) {
719 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
720 tty_ldisc_reinit(tty, N_TTY) < 0)
721 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
722 } else
723 tty_ldisc_kill(tty);
724 }
725 tty_ldisc_unlock(tty);
726}
727
728/**
729 * tty_ldisc_setup - open line discipline
730 * @tty: tty being shut down
731 * @o_tty: pair tty for pty/tty pairs
732 *
733 * Called during the initial open of a tty/pty pair in order to set up the line
734 * disciplines and bind them to the @tty. This has no locking issues as the
735 * device isn't yet active.
736 */
737int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
738{
739 int retval = tty_ldisc_open(tty, tty->ldisc);
740
741 if (retval)
742 return retval;
743
744 if (o_tty) {
745 /*
746 * Called without o_tty->ldisc_sem held, as o_tty has been
747 * just allocated and no one has a reference to it.
748 */
749 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
750 if (retval) {
751 tty_ldisc_close(tty, tty->ldisc);
752 return retval;
753 }
754 }
755 return 0;
756}
757
758/**
759 * tty_ldisc_release - release line discipline
760 * @tty: tty being shut down (or one end of pty pair)
761 *
762 * Called during the final close of a tty or a pty pair in order to shut down
763 * the line discpline layer. On exit, each tty's ldisc is %NULL.
764 */
765void tty_ldisc_release(struct tty_struct *tty)
766{
767 struct tty_struct *o_tty = tty->link;
768
769 /*
770 * Shutdown this line discipline. As this is the final close,
771 * it does not race with the set_ldisc code path.
772 */
773
774 tty_ldisc_lock_pair(tty, o_tty);
775 tty_ldisc_kill(tty);
776 if (o_tty)
777 tty_ldisc_kill(o_tty);
778 tty_ldisc_unlock_pair(tty, o_tty);
779
780 /*
781 * And the memory resources remaining (buffers, termios) will be
782 * disposed of when the kref hits zero
783 */
784
785 tty_ldisc_debug(tty, "released\n");
786}
787
788/**
789 * tty_ldisc_init - ldisc setup for new tty
790 * @tty: tty being allocated
791 *
792 * Set up the line discipline objects for a newly allocated tty. Note that the
793 * tty structure is not completely set up when this call is made.
794 */
795int tty_ldisc_init(struct tty_struct *tty)
796{
797 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
798
799 if (IS_ERR(ld))
800 return PTR_ERR(ld);
801 tty->ldisc = ld;
802 return 0;
803}
804
805/**
806 * tty_ldisc_deinit - ldisc cleanup for new tty
807 * @tty: tty that was allocated recently
808 *
809 * The tty structure must not be completely set up (tty_ldisc_setup()) when
810 * this call is made.
811 */
812void tty_ldisc_deinit(struct tty_struct *tty)
813{
814 /* no ldisc_sem, tty is being destroyed */
815 if (tty->ldisc)
816 tty_ldisc_put(tty->ldisc);
817 tty->ldisc = NULL;
818}
1#include <linux/types.h>
2#include <linux/major.h>
3#include <linux/errno.h>
4#include <linux/signal.h>
5#include <linux/fcntl.h>
6#include <linux/sched.h>
7#include <linux/interrupt.h>
8#include <linux/tty.h>
9#include <linux/tty_driver.h>
10#include <linux/tty_flip.h>
11#include <linux/devpts_fs.h>
12#include <linux/file.h>
13#include <linux/console.h>
14#include <linux/timer.h>
15#include <linux/ctype.h>
16#include <linux/kd.h>
17#include <linux/mm.h>
18#include <linux/string.h>
19#include <linux/slab.h>
20#include <linux/poll.h>
21#include <linux/proc_fs.h>
22#include <linux/init.h>
23#include <linux/module.h>
24#include <linux/device.h>
25#include <linux/wait.h>
26#include <linux/bitops.h>
27#include <linux/delay.h>
28#include <linux/seq_file.h>
29
30#include <linux/uaccess.h>
31#include <asm/system.h>
32
33#include <linux/kbd_kern.h>
34#include <linux/vt_kern.h>
35#include <linux/selection.h>
36
37#include <linux/kmod.h>
38#include <linux/nsproxy.h>
39
40/*
41 * This guards the refcounted line discipline lists. The lock
42 * must be taken with irqs off because there are hangup path
43 * callers who will do ldisc lookups and cannot sleep.
44 */
45
46static DEFINE_SPINLOCK(tty_ldisc_lock);
47static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
48static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
49/* Line disc dispatch table */
50static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
51
52static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
53{
54 if (ld)
55 atomic_inc(&ld->users);
56 return ld;
57}
58
59static void put_ldisc(struct tty_ldisc *ld)
60{
61 unsigned long flags;
62
63 if (WARN_ON_ONCE(!ld))
64 return;
65
66 /*
67 * If this is the last user, free the ldisc, and
68 * release the ldisc ops.
69 *
70 * We really want an "atomic_dec_and_lock_irqsave()",
71 * but we don't have it, so this does it by hand.
72 */
73 local_irq_save(flags);
74 if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
75 struct tty_ldisc_ops *ldo = ld->ops;
76
77 ldo->refcount--;
78 module_put(ldo->owner);
79 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
80
81 kfree(ld);
82 return;
83 }
84 local_irq_restore(flags);
85 wake_up(&tty_ldisc_idle);
86}
87
88/**
89 * tty_register_ldisc - install a line discipline
90 * @disc: ldisc number
91 * @new_ldisc: pointer to the ldisc object
92 *
93 * Installs a new line discipline into the kernel. The discipline
94 * is set up as unreferenced and then made available to the kernel
95 * from this point onwards.
96 *
97 * Locking:
98 * takes tty_ldisc_lock to guard against ldisc races
99 */
100
101int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
102{
103 unsigned long flags;
104 int ret = 0;
105
106 if (disc < N_TTY || disc >= NR_LDISCS)
107 return -EINVAL;
108
109 spin_lock_irqsave(&tty_ldisc_lock, flags);
110 tty_ldiscs[disc] = new_ldisc;
111 new_ldisc->num = disc;
112 new_ldisc->refcount = 0;
113 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
114
115 return ret;
116}
117EXPORT_SYMBOL(tty_register_ldisc);
118
119/**
120 * tty_unregister_ldisc - unload a line discipline
121 * @disc: ldisc number
122 * @new_ldisc: pointer to the ldisc object
123 *
124 * Remove a line discipline from the kernel providing it is not
125 * currently in use.
126 *
127 * Locking:
128 * takes tty_ldisc_lock to guard against ldisc races
129 */
130
131int tty_unregister_ldisc(int disc)
132{
133 unsigned long flags;
134 int ret = 0;
135
136 if (disc < N_TTY || disc >= NR_LDISCS)
137 return -EINVAL;
138
139 spin_lock_irqsave(&tty_ldisc_lock, flags);
140 if (tty_ldiscs[disc]->refcount)
141 ret = -EBUSY;
142 else
143 tty_ldiscs[disc] = NULL;
144 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
145
146 return ret;
147}
148EXPORT_SYMBOL(tty_unregister_ldisc);
149
150static struct tty_ldisc_ops *get_ldops(int disc)
151{
152 unsigned long flags;
153 struct tty_ldisc_ops *ldops, *ret;
154
155 spin_lock_irqsave(&tty_ldisc_lock, flags);
156 ret = ERR_PTR(-EINVAL);
157 ldops = tty_ldiscs[disc];
158 if (ldops) {
159 ret = ERR_PTR(-EAGAIN);
160 if (try_module_get(ldops->owner)) {
161 ldops->refcount++;
162 ret = ldops;
163 }
164 }
165 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
166 return ret;
167}
168
169static void put_ldops(struct tty_ldisc_ops *ldops)
170{
171 unsigned long flags;
172
173 spin_lock_irqsave(&tty_ldisc_lock, flags);
174 ldops->refcount--;
175 module_put(ldops->owner);
176 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
177}
178
179/**
180 * tty_ldisc_get - take a reference to an ldisc
181 * @disc: ldisc number
182 *
183 * Takes a reference to a line discipline. Deals with refcounts and
184 * module locking counts. Returns NULL if the discipline is not available.
185 * Returns a pointer to the discipline and bumps the ref count if it is
186 * available
187 *
188 * Locking:
189 * takes tty_ldisc_lock to guard against ldisc races
190 */
191
192static struct tty_ldisc *tty_ldisc_get(int disc)
193{
194 struct tty_ldisc *ld;
195 struct tty_ldisc_ops *ldops;
196
197 if (disc < N_TTY || disc >= NR_LDISCS)
198 return ERR_PTR(-EINVAL);
199
200 /*
201 * Get the ldisc ops - we may need to request them to be loaded
202 * dynamically and try again.
203 */
204 ldops = get_ldops(disc);
205 if (IS_ERR(ldops)) {
206 request_module("tty-ldisc-%d", disc);
207 ldops = get_ldops(disc);
208 if (IS_ERR(ldops))
209 return ERR_CAST(ldops);
210 }
211
212 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
213 if (ld == NULL) {
214 put_ldops(ldops);
215 return ERR_PTR(-ENOMEM);
216 }
217
218 ld->ops = ldops;
219 atomic_set(&ld->users, 1);
220 return ld;
221}
222
223static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
224{
225 return (*pos < NR_LDISCS) ? pos : NULL;
226}
227
228static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
229{
230 (*pos)++;
231 return (*pos < NR_LDISCS) ? pos : NULL;
232}
233
234static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
235{
236}
237
238static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
239{
240 int i = *(loff_t *)v;
241 struct tty_ldisc_ops *ldops;
242
243 ldops = get_ldops(i);
244 if (IS_ERR(ldops))
245 return 0;
246 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
247 put_ldops(ldops);
248 return 0;
249}
250
251static const struct seq_operations tty_ldiscs_seq_ops = {
252 .start = tty_ldiscs_seq_start,
253 .next = tty_ldiscs_seq_next,
254 .stop = tty_ldiscs_seq_stop,
255 .show = tty_ldiscs_seq_show,
256};
257
258static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
259{
260 return seq_open(file, &tty_ldiscs_seq_ops);
261}
262
263const struct file_operations tty_ldiscs_proc_fops = {
264 .owner = THIS_MODULE,
265 .open = proc_tty_ldiscs_open,
266 .read = seq_read,
267 .llseek = seq_lseek,
268 .release = seq_release,
269};
270
271/**
272 * tty_ldisc_assign - set ldisc on a tty
273 * @tty: tty to assign
274 * @ld: line discipline
275 *
276 * Install an instance of a line discipline into a tty structure. The
277 * ldisc must have a reference count above zero to ensure it remains.
278 * The tty instance refcount starts at zero.
279 *
280 * Locking:
281 * Caller must hold references
282 */
283
284static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
285{
286 tty->ldisc = ld;
287}
288
289/**
290 * tty_ldisc_try - internal helper
291 * @tty: the tty
292 *
293 * Make a single attempt to grab and bump the refcount on
294 * the tty ldisc. Return 0 on failure or 1 on success. This is
295 * used to implement both the waiting and non waiting versions
296 * of tty_ldisc_ref
297 *
298 * Locking: takes tty_ldisc_lock
299 */
300
301static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
302{
303 unsigned long flags;
304 struct tty_ldisc *ld;
305
306 spin_lock_irqsave(&tty_ldisc_lock, flags);
307 ld = NULL;
308 if (test_bit(TTY_LDISC, &tty->flags))
309 ld = get_ldisc(tty->ldisc);
310 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
311 return ld;
312}
313
314/**
315 * tty_ldisc_ref_wait - wait for the tty ldisc
316 * @tty: tty device
317 *
318 * Dereference the line discipline for the terminal and take a
319 * reference to it. If the line discipline is in flux then
320 * wait patiently until it changes.
321 *
322 * Note: Must not be called from an IRQ/timer context. The caller
323 * must also be careful not to hold other locks that will deadlock
324 * against a discipline change, such as an existing ldisc reference
325 * (which we check for)
326 *
327 * Locking: call functions take tty_ldisc_lock
328 */
329
330struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
331{
332 struct tty_ldisc *ld;
333
334 /* wait_event is a macro */
335 wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
336 return ld;
337}
338EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
339
340/**
341 * tty_ldisc_ref - get the tty ldisc
342 * @tty: tty device
343 *
344 * Dereference the line discipline for the terminal and take a
345 * reference to it. If the line discipline is in flux then
346 * return NULL. Can be called from IRQ and timer functions.
347 *
348 * Locking: called functions take tty_ldisc_lock
349 */
350
351struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
352{
353 return tty_ldisc_try(tty);
354}
355EXPORT_SYMBOL_GPL(tty_ldisc_ref);
356
357/**
358 * tty_ldisc_deref - free a tty ldisc reference
359 * @ld: reference to free up
360 *
361 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
362 * be called in IRQ context.
363 *
364 * Locking: takes tty_ldisc_lock
365 */
366
367void tty_ldisc_deref(struct tty_ldisc *ld)
368{
369 put_ldisc(ld);
370}
371EXPORT_SYMBOL_GPL(tty_ldisc_deref);
372
373static inline void tty_ldisc_put(struct tty_ldisc *ld)
374{
375 put_ldisc(ld);
376}
377
378/**
379 * tty_ldisc_enable - allow ldisc use
380 * @tty: terminal to activate ldisc on
381 *
382 * Set the TTY_LDISC flag when the line discipline can be called
383 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
384 * changing flag to indicate any ldisc change is now over.
385 *
386 * Note: nobody should set the TTY_LDISC bit except via this function.
387 * Clearing directly is allowed.
388 */
389
390void tty_ldisc_enable(struct tty_struct *tty)
391{
392 set_bit(TTY_LDISC, &tty->flags);
393 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
394 wake_up(&tty_ldisc_wait);
395}
396
397/**
398 * tty_ldisc_flush - flush line discipline queue
399 * @tty: tty
400 *
401 * Flush the line discipline queue (if any) for this tty. If there
402 * is no line discipline active this is a no-op.
403 */
404
405void tty_ldisc_flush(struct tty_struct *tty)
406{
407 struct tty_ldisc *ld = tty_ldisc_ref(tty);
408 if (ld) {
409 if (ld->ops->flush_buffer)
410 ld->ops->flush_buffer(tty);
411 tty_ldisc_deref(ld);
412 }
413 tty_buffer_flush(tty);
414}
415EXPORT_SYMBOL_GPL(tty_ldisc_flush);
416
417/**
418 * tty_set_termios_ldisc - set ldisc field
419 * @tty: tty structure
420 * @num: line discipline number
421 *
422 * This is probably overkill for real world processors but
423 * they are not on hot paths so a little discipline won't do
424 * any harm.
425 *
426 * Locking: takes termios_mutex
427 */
428
429static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
430{
431 mutex_lock(&tty->termios_mutex);
432 tty->termios->c_line = num;
433 mutex_unlock(&tty->termios_mutex);
434}
435
436/**
437 * tty_ldisc_open - open a line discipline
438 * @tty: tty we are opening the ldisc on
439 * @ld: discipline to open
440 *
441 * A helper opening method. Also a convenient debugging and check
442 * point.
443 *
444 * Locking: always called with BTM already held.
445 */
446
447static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
448{
449 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
450 if (ld->ops->open) {
451 int ret;
452 /* BTM here locks versus a hangup event */
453 WARN_ON(!tty_locked());
454 ret = ld->ops->open(tty);
455 if (ret)
456 clear_bit(TTY_LDISC_OPEN, &tty->flags);
457 return ret;
458 }
459 return 0;
460}
461
462/**
463 * tty_ldisc_close - close a line discipline
464 * @tty: tty we are opening the ldisc on
465 * @ld: discipline to close
466 *
467 * A helper close method. Also a convenient debugging and check
468 * point.
469 */
470
471static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
472{
473 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
474 clear_bit(TTY_LDISC_OPEN, &tty->flags);
475 if (ld->ops->close)
476 ld->ops->close(tty);
477}
478
479/**
480 * tty_ldisc_restore - helper for tty ldisc change
481 * @tty: tty to recover
482 * @old: previous ldisc
483 *
484 * Restore the previous line discipline or N_TTY when a line discipline
485 * change fails due to an open error
486 */
487
488static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
489{
490 char buf[64];
491 struct tty_ldisc *new_ldisc;
492 int r;
493
494 /* There is an outstanding reference here so this is safe */
495 old = tty_ldisc_get(old->ops->num);
496 WARN_ON(IS_ERR(old));
497 tty_ldisc_assign(tty, old);
498 tty_set_termios_ldisc(tty, old->ops->num);
499 if (tty_ldisc_open(tty, old) < 0) {
500 tty_ldisc_put(old);
501 /* This driver is always present */
502 new_ldisc = tty_ldisc_get(N_TTY);
503 if (IS_ERR(new_ldisc))
504 panic("n_tty: get");
505 tty_ldisc_assign(tty, new_ldisc);
506 tty_set_termios_ldisc(tty, N_TTY);
507 r = tty_ldisc_open(tty, new_ldisc);
508 if (r < 0)
509 panic("Couldn't open N_TTY ldisc for "
510 "%s --- error %d.",
511 tty_name(tty, buf), r);
512 }
513}
514
515/**
516 * tty_ldisc_halt - shut down the line discipline
517 * @tty: tty device
518 *
519 * Shut down the line discipline and work queue for this tty device.
520 * The TTY_LDISC flag being cleared ensures no further references can
521 * be obtained while the delayed work queue halt ensures that no more
522 * data is fed to the ldisc.
523 *
524 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
525 * in order to make sure any currently executing ldisc work is also
526 * flushed.
527 */
528
529static int tty_ldisc_halt(struct tty_struct *tty)
530{
531 clear_bit(TTY_LDISC, &tty->flags);
532 return cancel_work_sync(&tty->buf.work);
533}
534
535/**
536 * tty_ldisc_flush_works - flush all works of a tty
537 * @tty: tty device to flush works for
538 *
539 * Sync flush all works belonging to @tty.
540 */
541static void tty_ldisc_flush_works(struct tty_struct *tty)
542{
543 flush_work_sync(&tty->hangup_work);
544 flush_work_sync(&tty->SAK_work);
545 flush_work_sync(&tty->buf.work);
546}
547
548/**
549 * tty_ldisc_wait_idle - wait for the ldisc to become idle
550 * @tty: tty to wait for
551 *
552 * Wait for the line discipline to become idle. The discipline must
553 * have been halted for this to guarantee it remains idle.
554 */
555static int tty_ldisc_wait_idle(struct tty_struct *tty)
556{
557 int ret;
558 ret = wait_event_timeout(tty_ldisc_idle,
559 atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
560 if (ret < 0)
561 return ret;
562 return ret > 0 ? 0 : -EBUSY;
563}
564
565/**
566 * tty_set_ldisc - set line discipline
567 * @tty: the terminal to set
568 * @ldisc: the line discipline
569 *
570 * Set the discipline of a tty line. Must be called from a process
571 * context. The ldisc change logic has to protect itself against any
572 * overlapping ldisc change (including on the other end of pty pairs),
573 * the close of one side of a tty/pty pair, and eventually hangup.
574 *
575 * Locking: takes tty_ldisc_lock, termios_mutex
576 */
577
578int tty_set_ldisc(struct tty_struct *tty, int ldisc)
579{
580 int retval;
581 struct tty_ldisc *o_ldisc, *new_ldisc;
582 int work, o_work = 0;
583 struct tty_struct *o_tty;
584
585 new_ldisc = tty_ldisc_get(ldisc);
586 if (IS_ERR(new_ldisc))
587 return PTR_ERR(new_ldisc);
588
589 tty_lock();
590 /*
591 * We need to look at the tty locking here for pty/tty pairs
592 * when both sides try to change in parallel.
593 */
594
595 o_tty = tty->link; /* o_tty is the pty side or NULL */
596
597
598 /*
599 * Check the no-op case
600 */
601
602 if (tty->ldisc->ops->num == ldisc) {
603 tty_unlock();
604 tty_ldisc_put(new_ldisc);
605 return 0;
606 }
607
608 tty_unlock();
609 /*
610 * Problem: What do we do if this blocks ?
611 * We could deadlock here
612 */
613
614 tty_wait_until_sent(tty, 0);
615
616 tty_lock();
617 mutex_lock(&tty->ldisc_mutex);
618
619 /*
620 * We could be midstream of another ldisc change which has
621 * dropped the lock during processing. If so we need to wait.
622 */
623
624 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
625 mutex_unlock(&tty->ldisc_mutex);
626 tty_unlock();
627 wait_event(tty_ldisc_wait,
628 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
629 tty_lock();
630 mutex_lock(&tty->ldisc_mutex);
631 }
632
633 set_bit(TTY_LDISC_CHANGING, &tty->flags);
634
635 /*
636 * No more input please, we are switching. The new ldisc
637 * will update this value in the ldisc open function
638 */
639
640 tty->receive_room = 0;
641
642 o_ldisc = tty->ldisc;
643
644 tty_unlock();
645 /*
646 * Make sure we don't change while someone holds a
647 * reference to the line discipline. The TTY_LDISC bit
648 * prevents anyone taking a reference once it is clear.
649 * We need the lock to avoid racing reference takers.
650 *
651 * We must clear the TTY_LDISC bit here to avoid a livelock
652 * with a userspace app continually trying to use the tty in
653 * parallel to the change and re-referencing the tty.
654 */
655
656 work = tty_ldisc_halt(tty);
657 if (o_tty)
658 o_work = tty_ldisc_halt(o_tty);
659
660 /*
661 * Wait for ->hangup_work and ->buf.work handlers to terminate.
662 * We must drop the mutex here in case a hangup is also in process.
663 */
664
665 mutex_unlock(&tty->ldisc_mutex);
666
667 tty_ldisc_flush_works(tty);
668
669 retval = tty_ldisc_wait_idle(tty);
670
671 tty_lock();
672 mutex_lock(&tty->ldisc_mutex);
673
674 /* handle wait idle failure locked */
675 if (retval) {
676 tty_ldisc_put(new_ldisc);
677 goto enable;
678 }
679
680 if (test_bit(TTY_HUPPED, &tty->flags)) {
681 /* We were raced by the hangup method. It will have stomped
682 the ldisc data and closed the ldisc down */
683 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
684 mutex_unlock(&tty->ldisc_mutex);
685 tty_ldisc_put(new_ldisc);
686 tty_unlock();
687 return -EIO;
688 }
689
690 /* Shutdown the current discipline. */
691 tty_ldisc_close(tty, o_ldisc);
692
693 /* Now set up the new line discipline. */
694 tty_ldisc_assign(tty, new_ldisc);
695 tty_set_termios_ldisc(tty, ldisc);
696
697 retval = tty_ldisc_open(tty, new_ldisc);
698 if (retval < 0) {
699 /* Back to the old one or N_TTY if we can't */
700 tty_ldisc_put(new_ldisc);
701 tty_ldisc_restore(tty, o_ldisc);
702 }
703
704 /* At this point we hold a reference to the new ldisc and a
705 a reference to the old ldisc. If we ended up flipping back
706 to the existing ldisc we have two references to it */
707
708 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
709 tty->ops->set_ldisc(tty);
710
711 tty_ldisc_put(o_ldisc);
712
713enable:
714 /*
715 * Allow ldisc referencing to occur again
716 */
717
718 tty_ldisc_enable(tty);
719 if (o_tty)
720 tty_ldisc_enable(o_tty);
721
722 /* Restart the work queue in case no characters kick it off. Safe if
723 already running */
724 if (work)
725 schedule_work(&tty->buf.work);
726 if (o_work)
727 schedule_work(&o_tty->buf.work);
728 mutex_unlock(&tty->ldisc_mutex);
729 tty_unlock();
730 return retval;
731}
732
733/**
734 * tty_reset_termios - reset terminal state
735 * @tty: tty to reset
736 *
737 * Restore a terminal to the driver default state.
738 */
739
740static void tty_reset_termios(struct tty_struct *tty)
741{
742 mutex_lock(&tty->termios_mutex);
743 *tty->termios = tty->driver->init_termios;
744 tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
745 tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
746 mutex_unlock(&tty->termios_mutex);
747}
748
749
750/**
751 * tty_ldisc_reinit - reinitialise the tty ldisc
752 * @tty: tty to reinit
753 * @ldisc: line discipline to reinitialize
754 *
755 * Switch the tty to a line discipline and leave the ldisc
756 * state closed
757 */
758
759static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
760{
761 struct tty_ldisc *ld = tty_ldisc_get(ldisc);
762
763 if (IS_ERR(ld))
764 return -1;
765
766 WARN_ON_ONCE(tty_ldisc_wait_idle(tty));
767
768 tty_ldisc_close(tty, tty->ldisc);
769 tty_ldisc_put(tty->ldisc);
770 tty->ldisc = NULL;
771 /*
772 * Switch the line discipline back
773 */
774 tty_ldisc_assign(tty, ld);
775 tty_set_termios_ldisc(tty, ldisc);
776
777 return 0;
778}
779
780/**
781 * tty_ldisc_hangup - hangup ldisc reset
782 * @tty: tty being hung up
783 *
784 * Some tty devices reset their termios when they receive a hangup
785 * event. In that situation we must also switch back to N_TTY properly
786 * before we reset the termios data.
787 *
788 * Locking: We can take the ldisc mutex as the rest of the code is
789 * careful to allow for this.
790 *
791 * In the pty pair case this occurs in the close() path of the
792 * tty itself so we must be careful about locking rules.
793 */
794
795void tty_ldisc_hangup(struct tty_struct *tty)
796{
797 struct tty_ldisc *ld;
798 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
799 int err = 0;
800
801 /*
802 * FIXME! What are the locking issues here? This may me overdoing
803 * things... This question is especially important now that we've
804 * removed the irqlock.
805 */
806 ld = tty_ldisc_ref(tty);
807 if (ld != NULL) {
808 /* We may have no line discipline at this point */
809 if (ld->ops->flush_buffer)
810 ld->ops->flush_buffer(tty);
811 tty_driver_flush_buffer(tty);
812 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
813 ld->ops->write_wakeup)
814 ld->ops->write_wakeup(tty);
815 if (ld->ops->hangup)
816 ld->ops->hangup(tty);
817 tty_ldisc_deref(ld);
818 }
819 /*
820 * FIXME: Once we trust the LDISC code better we can wait here for
821 * ldisc completion and fix the driver call race
822 */
823 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
824 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
825 /*
826 * Shutdown the current line discipline, and reset it to
827 * N_TTY if need be.
828 *
829 * Avoid racing set_ldisc or tty_ldisc_release
830 */
831 mutex_lock(&tty->ldisc_mutex);
832
833 /*
834 * this is like tty_ldisc_halt, but we need to give up
835 * the BTM before calling cancel_work_sync, which may
836 * need to wait for another function taking the BTM
837 */
838 clear_bit(TTY_LDISC, &tty->flags);
839 tty_unlock();
840 cancel_work_sync(&tty->buf.work);
841 mutex_unlock(&tty->ldisc_mutex);
842
843 tty_lock();
844 mutex_lock(&tty->ldisc_mutex);
845
846 /* At this point we have a closed ldisc and we want to
847 reopen it. We could defer this to the next open but
848 it means auditing a lot of other paths so this is
849 a FIXME */
850 if (tty->ldisc) { /* Not yet closed */
851 if (reset == 0) {
852
853 if (!tty_ldisc_reinit(tty, tty->termios->c_line))
854 err = tty_ldisc_open(tty, tty->ldisc);
855 else
856 err = 1;
857 }
858 /* If the re-open fails or we reset then go to N_TTY. The
859 N_TTY open cannot fail */
860 if (reset || err) {
861 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
862 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
863 }
864 tty_ldisc_enable(tty);
865 }
866 mutex_unlock(&tty->ldisc_mutex);
867 if (reset)
868 tty_reset_termios(tty);
869}
870
871/**
872 * tty_ldisc_setup - open line discipline
873 * @tty: tty being shut down
874 * @o_tty: pair tty for pty/tty pairs
875 *
876 * Called during the initial open of a tty/pty pair in order to set up the
877 * line disciplines and bind them to the tty. This has no locking issues
878 * as the device isn't yet active.
879 */
880
881int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
882{
883 struct tty_ldisc *ld = tty->ldisc;
884 int retval;
885
886 retval = tty_ldisc_open(tty, ld);
887 if (retval)
888 return retval;
889
890 if (o_tty) {
891 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
892 if (retval) {
893 tty_ldisc_close(tty, ld);
894 return retval;
895 }
896 tty_ldisc_enable(o_tty);
897 }
898 tty_ldisc_enable(tty);
899 return 0;
900}
901/**
902 * tty_ldisc_release - release line discipline
903 * @tty: tty being shut down
904 * @o_tty: pair tty for pty/tty pairs
905 *
906 * Called during the final close of a tty/pty pair in order to shut down
907 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
908 * ldisc has not been opened.
909 */
910
911void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
912{
913 /*
914 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
915 * kill any delayed work. As this is the final close it does not
916 * race with the set_ldisc code path.
917 */
918
919 tty_unlock();
920 tty_ldisc_halt(tty);
921 tty_ldisc_flush_works(tty);
922 tty_lock();
923
924 mutex_lock(&tty->ldisc_mutex);
925 /*
926 * Now kill off the ldisc
927 */
928 tty_ldisc_close(tty, tty->ldisc);
929 tty_ldisc_put(tty->ldisc);
930 /* Force an oops if we mess this up */
931 tty->ldisc = NULL;
932
933 /* Ensure the next open requests the N_TTY ldisc */
934 tty_set_termios_ldisc(tty, N_TTY);
935 mutex_unlock(&tty->ldisc_mutex);
936
937 /* This will need doing differently if we need to lock */
938 if (o_tty)
939 tty_ldisc_release(o_tty, NULL);
940
941 /* And the memory resources remaining (buffers, termios) will be
942 disposed of when the kref hits zero */
943}
944
945/**
946 * tty_ldisc_init - ldisc setup for new tty
947 * @tty: tty being allocated
948 *
949 * Set up the line discipline objects for a newly allocated tty. Note that
950 * the tty structure is not completely set up when this call is made.
951 */
952
953void tty_ldisc_init(struct tty_struct *tty)
954{
955 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
956 if (IS_ERR(ld))
957 panic("n_tty: init_tty");
958 tty_ldisc_assign(tty, ld);
959}
960
961/**
962 * tty_ldisc_init - ldisc cleanup for new tty
963 * @tty: tty that was allocated recently
964 *
965 * The tty structure must not becompletely set up (tty_ldisc_setup) when
966 * this call is made.
967 */
968void tty_ldisc_deinit(struct tty_struct *tty)
969{
970 put_ldisc(tty->ldisc);
971 tty_ldisc_assign(tty, NULL);
972}
973
974void tty_ldisc_begin(void)
975{
976 /* Setup the default TTY line discipline. */
977 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
978}