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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}
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}