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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 | |
29 | static DEFINE_RAW_SPINLOCK(tty_ldisc_lock); |
30 | static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait); |
31 | /* Line disc dispatch table */ |
32 | static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS]; |
33 | |
34 | static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld) |
35 | { |
36 | if (ld) |
37 | atomic_inc(&ld->users); |
38 | return ld; |
39 | } |
40 | |
41 | static 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_raw_lock_irqsave()", |
53 | * but we don't have it, so this does it by hand. |
54 | */ |
55 | raw_spin_lock_irqsave(&tty_ldisc_lock, flags); |
56 | if (atomic_dec_and_test(&ld->users)) { |
57 | struct tty_ldisc_ops *ldo = ld->ops; |
58 | |
59 | ldo->refcount--; |
60 | module_put(ldo->owner); |
61 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
62 | |
63 | kfree(ld); |
64 | return; |
65 | } |
66 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
67 | |
68 | if (waitqueue_active(&ld->wq_idle)) |
69 | wake_up(&ld->wq_idle); |
70 | } |
71 | |
72 | /** |
73 | * tty_register_ldisc - install a line discipline |
74 | * @disc: ldisc number |
75 | * @new_ldisc: pointer to the ldisc object |
76 | * |
77 | * Installs a new line discipline into the kernel. The discipline |
78 | * is set up as unreferenced and then made available to the kernel |
79 | * from this point onwards. |
80 | * |
81 | * Locking: |
82 | * takes tty_ldisc_lock to guard against ldisc races |
83 | */ |
84 | |
85 | int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc) |
86 | { |
87 | unsigned long flags; |
88 | int ret = 0; |
89 | |
90 | if (disc < N_TTY || disc >= NR_LDISCS) |
91 | return -EINVAL; |
92 | |
93 | raw_spin_lock_irqsave(&tty_ldisc_lock, flags); |
94 | tty_ldiscs[disc] = new_ldisc; |
95 | new_ldisc->num = disc; |
96 | new_ldisc->refcount = 0; |
97 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
98 | |
99 | return ret; |
100 | } |
101 | EXPORT_SYMBOL(tty_register_ldisc); |
102 | |
103 | /** |
104 | * tty_unregister_ldisc - unload a line discipline |
105 | * @disc: ldisc number |
106 | * @new_ldisc: pointer to the ldisc object |
107 | * |
108 | * Remove a line discipline from the kernel providing it is not |
109 | * currently in use. |
110 | * |
111 | * Locking: |
112 | * takes tty_ldisc_lock to guard against ldisc races |
113 | */ |
114 | |
115 | int tty_unregister_ldisc(int disc) |
116 | { |
117 | unsigned long flags; |
118 | int ret = 0; |
119 | |
120 | if (disc < N_TTY || disc >= NR_LDISCS) |
121 | return -EINVAL; |
122 | |
123 | raw_spin_lock_irqsave(&tty_ldisc_lock, flags); |
124 | if (tty_ldiscs[disc]->refcount) |
125 | ret = -EBUSY; |
126 | else |
127 | tty_ldiscs[disc] = NULL; |
128 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
129 | |
130 | return ret; |
131 | } |
132 | EXPORT_SYMBOL(tty_unregister_ldisc); |
133 | |
134 | static struct tty_ldisc_ops *get_ldops(int disc) |
135 | { |
136 | unsigned long flags; |
137 | struct tty_ldisc_ops *ldops, *ret; |
138 | |
139 | raw_spin_lock_irqsave(&tty_ldisc_lock, flags); |
140 | ret = ERR_PTR(-EINVAL); |
141 | ldops = tty_ldiscs[disc]; |
142 | if (ldops) { |
143 | ret = ERR_PTR(-EAGAIN); |
144 | if (try_module_get(ldops->owner)) { |
145 | ldops->refcount++; |
146 | ret = ldops; |
147 | } |
148 | } |
149 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
150 | return ret; |
151 | } |
152 | |
153 | static void put_ldops(struct tty_ldisc_ops *ldops) |
154 | { |
155 | unsigned long flags; |
156 | |
157 | raw_spin_lock_irqsave(&tty_ldisc_lock, flags); |
158 | ldops->refcount--; |
159 | module_put(ldops->owner); |
160 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
161 | } |
162 | |
163 | /** |
164 | * tty_ldisc_get - take a reference to an ldisc |
165 | * @disc: ldisc number |
166 | * |
167 | * Takes a reference to a line discipline. Deals with refcounts and |
168 | * module locking counts. Returns NULL if the discipline is not available. |
169 | * Returns a pointer to the discipline and bumps the ref count if it is |
170 | * available |
171 | * |
172 | * Locking: |
173 | * takes tty_ldisc_lock to guard against ldisc races |
174 | */ |
175 | |
176 | static struct tty_ldisc *tty_ldisc_get(int disc) |
177 | { |
178 | struct tty_ldisc *ld; |
179 | struct tty_ldisc_ops *ldops; |
180 | |
181 | if (disc < N_TTY || disc >= NR_LDISCS) |
182 | return ERR_PTR(-EINVAL); |
183 | |
184 | /* |
185 | * Get the ldisc ops - we may need to request them to be loaded |
186 | * dynamically and try again. |
187 | */ |
188 | ldops = get_ldops(disc); |
189 | if (IS_ERR(ldops)) { |
190 | request_module("tty-ldisc-%d", disc); |
191 | ldops = get_ldops(disc); |
192 | if (IS_ERR(ldops)) |
193 | return ERR_CAST(ldops); |
194 | } |
195 | |
196 | ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL); |
197 | if (ld == NULL) { |
198 | put_ldops(ldops); |
199 | return ERR_PTR(-ENOMEM); |
200 | } |
201 | |
202 | ld->ops = ldops; |
203 | atomic_set(&ld->users, 1); |
204 | init_waitqueue_head(&ld->wq_idle); |
205 | |
206 | return ld; |
207 | } |
208 | |
209 | static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos) |
210 | { |
211 | return (*pos < NR_LDISCS) ? pos : NULL; |
212 | } |
213 | |
214 | static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos) |
215 | { |
216 | (*pos)++; |
217 | return (*pos < NR_LDISCS) ? pos : NULL; |
218 | } |
219 | |
220 | static void tty_ldiscs_seq_stop(struct seq_file *m, void *v) |
221 | { |
222 | } |
223 | |
224 | static int tty_ldiscs_seq_show(struct seq_file *m, void *v) |
225 | { |
226 | int i = *(loff_t *)v; |
227 | struct tty_ldisc_ops *ldops; |
228 | |
229 | ldops = get_ldops(i); |
230 | if (IS_ERR(ldops)) |
231 | return 0; |
232 | seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i); |
233 | put_ldops(ldops); |
234 | return 0; |
235 | } |
236 | |
237 | static const struct seq_operations tty_ldiscs_seq_ops = { |
238 | .start = tty_ldiscs_seq_start, |
239 | .next = tty_ldiscs_seq_next, |
240 | .stop = tty_ldiscs_seq_stop, |
241 | .show = tty_ldiscs_seq_show, |
242 | }; |
243 | |
244 | static int proc_tty_ldiscs_open(struct inode *inode, struct file *file) |
245 | { |
246 | return seq_open(file, &tty_ldiscs_seq_ops); |
247 | } |
248 | |
249 | const struct file_operations tty_ldiscs_proc_fops = { |
250 | .owner = THIS_MODULE, |
251 | .open = proc_tty_ldiscs_open, |
252 | .read = seq_read, |
253 | .llseek = seq_lseek, |
254 | .release = seq_release, |
255 | }; |
256 | |
257 | /** |
258 | * tty_ldisc_assign - set ldisc on a tty |
259 | * @tty: tty to assign |
260 | * @ld: line discipline |
261 | * |
262 | * Install an instance of a line discipline into a tty structure. The |
263 | * ldisc must have a reference count above zero to ensure it remains. |
264 | * The tty instance refcount starts at zero. |
265 | * |
266 | * Locking: |
267 | * Caller must hold references |
268 | */ |
269 | |
270 | static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld) |
271 | { |
272 | tty->ldisc = ld; |
273 | } |
274 | |
275 | /** |
276 | * tty_ldisc_try - internal helper |
277 | * @tty: the tty |
278 | * |
279 | * Make a single attempt to grab and bump the refcount on |
280 | * the tty ldisc. Return 0 on failure or 1 on success. This is |
281 | * used to implement both the waiting and non waiting versions |
282 | * of tty_ldisc_ref |
283 | * |
284 | * Locking: takes tty_ldisc_lock |
285 | */ |
286 | |
287 | static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty) |
288 | { |
289 | unsigned long flags; |
290 | struct tty_ldisc *ld; |
291 | |
292 | raw_spin_lock_irqsave(&tty_ldisc_lock, flags); |
293 | ld = NULL; |
294 | if (test_bit(TTY_LDISC, &tty->flags)) |
295 | ld = get_ldisc(tty->ldisc); |
296 | raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); |
297 | return ld; |
298 | } |
299 | |
300 | /** |
301 | * tty_ldisc_ref_wait - wait for the tty ldisc |
302 | * @tty: tty device |
303 | * |
304 | * Dereference the line discipline for the terminal and take a |
305 | * reference to it. If the line discipline is in flux then |
306 | * wait patiently until it changes. |
307 | * |
308 | * Note: Must not be called from an IRQ/timer context. The caller |
309 | * must also be careful not to hold other locks that will deadlock |
310 | * against a discipline change, such as an existing ldisc reference |
311 | * (which we check for) |
312 | * |
313 | * Locking: call functions take tty_ldisc_lock |
314 | */ |
315 | |
316 | struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty) |
317 | { |
318 | struct tty_ldisc *ld; |
319 | |
320 | /* wait_event is a macro */ |
321 | wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL); |
322 | return ld; |
323 | } |
324 | EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait); |
325 | |
326 | /** |
327 | * tty_ldisc_ref - get the tty ldisc |
328 | * @tty: tty device |
329 | * |
330 | * Dereference the line discipline for the terminal and take a |
331 | * reference to it. If the line discipline is in flux then |
332 | * return NULL. Can be called from IRQ and timer functions. |
333 | * |
334 | * Locking: called functions take tty_ldisc_lock |
335 | */ |
336 | |
337 | struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty) |
338 | { |
339 | return tty_ldisc_try(tty); |
340 | } |
341 | EXPORT_SYMBOL_GPL(tty_ldisc_ref); |
342 | |
343 | /** |
344 | * tty_ldisc_deref - free a tty ldisc reference |
345 | * @ld: reference to free up |
346 | * |
347 | * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May |
348 | * be called in IRQ context. |
349 | * |
350 | * Locking: takes tty_ldisc_lock |
351 | */ |
352 | |
353 | void tty_ldisc_deref(struct tty_ldisc *ld) |
354 | { |
355 | put_ldisc(ld); |
356 | } |
357 | EXPORT_SYMBOL_GPL(tty_ldisc_deref); |
358 | |
359 | static inline void tty_ldisc_put(struct tty_ldisc *ld) |
360 | { |
361 | put_ldisc(ld); |
362 | } |
363 | |
364 | /** |
365 | * tty_ldisc_enable - allow ldisc use |
366 | * @tty: terminal to activate ldisc on |
367 | * |
368 | * Set the TTY_LDISC flag when the line discipline can be called |
369 | * again. Do necessary wakeups for existing sleepers. Clear the LDISC |
370 | * changing flag to indicate any ldisc change is now over. |
371 | * |
372 | * Note: nobody should set the TTY_LDISC bit except via this function. |
373 | * Clearing directly is allowed. |
374 | */ |
375 | |
376 | void tty_ldisc_enable(struct tty_struct *tty) |
377 | { |
378 | set_bit(TTY_LDISC, &tty->flags); |
379 | clear_bit(TTY_LDISC_CHANGING, &tty->flags); |
380 | wake_up(&tty_ldisc_wait); |
381 | } |
382 | |
383 | /** |
384 | * tty_ldisc_flush - flush line discipline queue |
385 | * @tty: tty |
386 | * |
387 | * Flush the line discipline queue (if any) for this tty. If there |
388 | * is no line discipline active this is a no-op. |
389 | */ |
390 | |
391 | void tty_ldisc_flush(struct tty_struct *tty) |
392 | { |
393 | struct tty_ldisc *ld = tty_ldisc_ref(tty); |
394 | if (ld) { |
395 | if (ld->ops->flush_buffer) |
396 | ld->ops->flush_buffer(tty); |
397 | tty_ldisc_deref(ld); |
398 | } |
399 | tty_buffer_flush(tty); |
400 | } |
401 | EXPORT_SYMBOL_GPL(tty_ldisc_flush); |
402 | |
403 | /** |
404 | * tty_set_termios_ldisc - set ldisc field |
405 | * @tty: tty structure |
406 | * @num: line discipline number |
407 | * |
408 | * This is probably overkill for real world processors but |
409 | * they are not on hot paths so a little discipline won't do |
410 | * any harm. |
411 | * |
412 | * Locking: takes termios_mutex |
413 | */ |
414 | |
415 | static void tty_set_termios_ldisc(struct tty_struct *tty, int num) |
416 | { |
417 | mutex_lock(&tty->termios_mutex); |
418 | tty->termios.c_line = num; |
419 | mutex_unlock(&tty->termios_mutex); |
420 | } |
421 | |
422 | /** |
423 | * tty_ldisc_open - open a line discipline |
424 | * @tty: tty we are opening the ldisc on |
425 | * @ld: discipline to open |
426 | * |
427 | * A helper opening method. Also a convenient debugging and check |
428 | * point. |
429 | * |
430 | * Locking: always called with BTM already held. |
431 | */ |
432 | |
433 | static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld) |
434 | { |
435 | WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags)); |
436 | if (ld->ops->open) { |
437 | int ret; |
438 | /* BTM here locks versus a hangup event */ |
439 | ret = ld->ops->open(tty); |
440 | if (ret) |
441 | clear_bit(TTY_LDISC_OPEN, &tty->flags); |
442 | return ret; |
443 | } |
444 | return 0; |
445 | } |
446 | |
447 | /** |
448 | * tty_ldisc_close - close a line discipline |
449 | * @tty: tty we are opening the ldisc on |
450 | * @ld: discipline to close |
451 | * |
452 | * A helper close method. Also a convenient debugging and check |
453 | * point. |
454 | */ |
455 | |
456 | static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld) |
457 | { |
458 | WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags)); |
459 | clear_bit(TTY_LDISC_OPEN, &tty->flags); |
460 | if (ld->ops->close) |
461 | ld->ops->close(tty); |
462 | } |
463 | |
464 | /** |
465 | * tty_ldisc_restore - helper for tty ldisc change |
466 | * @tty: tty to recover |
467 | * @old: previous ldisc |
468 | * |
469 | * Restore the previous line discipline or N_TTY when a line discipline |
470 | * change fails due to an open error |
471 | */ |
472 | |
473 | static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old) |
474 | { |
475 | char buf[64]; |
476 | struct tty_ldisc *new_ldisc; |
477 | int r; |
478 | |
479 | /* There is an outstanding reference here so this is safe */ |
480 | old = tty_ldisc_get(old->ops->num); |
481 | WARN_ON(IS_ERR(old)); |
482 | tty_ldisc_assign(tty, old); |
483 | tty_set_termios_ldisc(tty, old->ops->num); |
484 | if (tty_ldisc_open(tty, old) < 0) { |
485 | tty_ldisc_put(old); |
486 | /* This driver is always present */ |
487 | new_ldisc = tty_ldisc_get(N_TTY); |
488 | if (IS_ERR(new_ldisc)) |
489 | panic("n_tty: get"); |
490 | tty_ldisc_assign(tty, new_ldisc); |
491 | tty_set_termios_ldisc(tty, N_TTY); |
492 | r = tty_ldisc_open(tty, new_ldisc); |
493 | if (r < 0) |
494 | panic("Couldn't open N_TTY ldisc for " |
495 | "%s --- error %d.", |
496 | tty_name(tty, buf), r); |
497 | } |
498 | } |
499 | |
500 | /** |
501 | * tty_ldisc_halt - shut down the line discipline |
502 | * @tty: tty device |
503 | * |
504 | * Shut down the line discipline and work queue for this tty device. |
505 | * The TTY_LDISC flag being cleared ensures no further references can |
506 | * be obtained while the delayed work queue halt ensures that no more |
507 | * data is fed to the ldisc. |
508 | * |
509 | * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex) |
510 | * in order to make sure any currently executing ldisc work is also |
511 | * flushed. |
512 | */ |
513 | |
514 | static int tty_ldisc_halt(struct tty_struct *tty) |
515 | { |
516 | clear_bit(TTY_LDISC, &tty->flags); |
517 | return cancel_work_sync(&tty->port->buf.work); |
518 | } |
519 | |
520 | /** |
521 | * tty_ldisc_flush_works - flush all works of a tty |
522 | * @tty: tty device to flush works for |
523 | * |
524 | * Sync flush all works belonging to @tty. |
525 | */ |
526 | static void tty_ldisc_flush_works(struct tty_struct *tty) |
527 | { |
528 | flush_work(&tty->hangup_work); |
529 | flush_work(&tty->SAK_work); |
530 | flush_work(&tty->port->buf.work); |
531 | } |
532 | |
533 | /** |
534 | * tty_ldisc_wait_idle - wait for the ldisc to become idle |
535 | * @tty: tty to wait for |
536 | * @timeout: for how long to wait at most |
537 | * |
538 | * Wait for the line discipline to become idle. The discipline must |
539 | * have been halted for this to guarantee it remains idle. |
540 | */ |
541 | static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) |
542 | { |
543 | long ret; |
544 | ret = wait_event_timeout(tty->ldisc->wq_idle, |
545 | atomic_read(&tty->ldisc->users) == 1, timeout); |
546 | return ret > 0 ? 0 : -EBUSY; |
547 | } |
548 | |
549 | /** |
550 | * tty_set_ldisc - set line discipline |
551 | * @tty: the terminal to set |
552 | * @ldisc: the line discipline |
553 | * |
554 | * Set the discipline of a tty line. Must be called from a process |
555 | * context. The ldisc change logic has to protect itself against any |
556 | * overlapping ldisc change (including on the other end of pty pairs), |
557 | * the close of one side of a tty/pty pair, and eventually hangup. |
558 | * |
559 | * Locking: takes tty_ldisc_lock, termios_mutex |
560 | */ |
561 | |
562 | int tty_set_ldisc(struct tty_struct *tty, int ldisc) |
563 | { |
564 | int retval; |
565 | struct tty_ldisc *o_ldisc, *new_ldisc; |
566 | int work, o_work = 0; |
567 | struct tty_struct *o_tty; |
568 | |
569 | new_ldisc = tty_ldisc_get(ldisc); |
570 | if (IS_ERR(new_ldisc)) |
571 | return PTR_ERR(new_ldisc); |
572 | |
573 | tty_lock(tty); |
574 | /* |
575 | * We need to look at the tty locking here for pty/tty pairs |
576 | * when both sides try to change in parallel. |
577 | */ |
578 | |
579 | o_tty = tty->link; /* o_tty is the pty side or NULL */ |
580 | |
581 | |
582 | /* |
583 | * Check the no-op case |
584 | */ |
585 | |
586 | if (tty->ldisc->ops->num == ldisc) { |
587 | tty_unlock(tty); |
588 | tty_ldisc_put(new_ldisc); |
589 | return 0; |
590 | } |
591 | |
592 | tty_unlock(tty); |
593 | /* |
594 | * Problem: What do we do if this blocks ? |
595 | * We could deadlock here |
596 | */ |
597 | |
598 | tty_wait_until_sent(tty, 0); |
599 | |
600 | tty_lock(tty); |
601 | mutex_lock(&tty->ldisc_mutex); |
602 | |
603 | /* |
604 | * We could be midstream of another ldisc change which has |
605 | * dropped the lock during processing. If so we need to wait. |
606 | */ |
607 | |
608 | while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) { |
609 | mutex_unlock(&tty->ldisc_mutex); |
610 | tty_unlock(tty); |
611 | wait_event(tty_ldisc_wait, |
612 | test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0); |
613 | tty_lock(tty); |
614 | mutex_lock(&tty->ldisc_mutex); |
615 | } |
616 | |
617 | set_bit(TTY_LDISC_CHANGING, &tty->flags); |
618 | |
619 | /* |
620 | * No more input please, we are switching. The new ldisc |
621 | * will update this value in the ldisc open function |
622 | */ |
623 | |
624 | tty->receive_room = 0; |
625 | |
626 | o_ldisc = tty->ldisc; |
627 | |
628 | tty_unlock(tty); |
629 | /* |
630 | * Make sure we don't change while someone holds a |
631 | * reference to the line discipline. The TTY_LDISC bit |
632 | * prevents anyone taking a reference once it is clear. |
633 | * We need the lock to avoid racing reference takers. |
634 | * |
635 | * We must clear the TTY_LDISC bit here to avoid a livelock |
636 | * with a userspace app continually trying to use the tty in |
637 | * parallel to the change and re-referencing the tty. |
638 | */ |
639 | |
640 | work = tty_ldisc_halt(tty); |
641 | if (o_tty) |
642 | o_work = tty_ldisc_halt(o_tty); |
643 | |
644 | /* |
645 | * Wait for ->hangup_work and ->buf.work handlers to terminate. |
646 | * We must drop the mutex here in case a hangup is also in process. |
647 | */ |
648 | |
649 | mutex_unlock(&tty->ldisc_mutex); |
650 | |
651 | tty_ldisc_flush_works(tty); |
652 | |
653 | retval = tty_ldisc_wait_idle(tty, 5 * HZ); |
654 | |
655 | tty_lock(tty); |
656 | mutex_lock(&tty->ldisc_mutex); |
657 | |
658 | /* handle wait idle failure locked */ |
659 | if (retval) { |
660 | tty_ldisc_put(new_ldisc); |
661 | goto enable; |
662 | } |
663 | |
664 | if (test_bit(TTY_HUPPING, &tty->flags)) { |
665 | /* We were raced by the hangup method. It will have stomped |
666 | the ldisc data and closed the ldisc down */ |
667 | clear_bit(TTY_LDISC_CHANGING, &tty->flags); |
668 | mutex_unlock(&tty->ldisc_mutex); |
669 | tty_ldisc_put(new_ldisc); |
670 | tty_unlock(tty); |
671 | return -EIO; |
672 | } |
673 | |
674 | /* Shutdown the current discipline. */ |
675 | tty_ldisc_close(tty, o_ldisc); |
676 | |
677 | /* Now set up the new line discipline. */ |
678 | tty_ldisc_assign(tty, new_ldisc); |
679 | tty_set_termios_ldisc(tty, ldisc); |
680 | |
681 | retval = tty_ldisc_open(tty, new_ldisc); |
682 | if (retval < 0) { |
683 | /* Back to the old one or N_TTY if we can't */ |
684 | tty_ldisc_put(new_ldisc); |
685 | tty_ldisc_restore(tty, o_ldisc); |
686 | } |
687 | |
688 | /* At this point we hold a reference to the new ldisc and a |
689 | a reference to the old ldisc. If we ended up flipping back |
690 | to the existing ldisc we have two references to it */ |
691 | |
692 | if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc) |
693 | tty->ops->set_ldisc(tty); |
694 | |
695 | tty_ldisc_put(o_ldisc); |
696 | |
697 | enable: |
698 | /* |
699 | * Allow ldisc referencing to occur again |
700 | */ |
701 | |
702 | tty_ldisc_enable(tty); |
703 | if (o_tty) |
704 | tty_ldisc_enable(o_tty); |
705 | |
706 | /* Restart the work queue in case no characters kick it off. Safe if |
707 | already running */ |
708 | if (work) |
709 | schedule_work(&tty->port->buf.work); |
710 | if (o_work) |
711 | schedule_work(&o_tty->port->buf.work); |
712 | mutex_unlock(&tty->ldisc_mutex); |
713 | tty_unlock(tty); |
714 | return retval; |
715 | } |
716 | |
717 | /** |
718 | * tty_reset_termios - reset terminal state |
719 | * @tty: tty to reset |
720 | * |
721 | * Restore a terminal to the driver default state. |
722 | */ |
723 | |
724 | static void tty_reset_termios(struct tty_struct *tty) |
725 | { |
726 | mutex_lock(&tty->termios_mutex); |
727 | tty->termios = tty->driver->init_termios; |
728 | tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios); |
729 | tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios); |
730 | mutex_unlock(&tty->termios_mutex); |
731 | } |
732 | |
733 | |
734 | /** |
735 | * tty_ldisc_reinit - reinitialise the tty ldisc |
736 | * @tty: tty to reinit |
737 | * @ldisc: line discipline to reinitialize |
738 | * |
739 | * Switch the tty to a line discipline and leave the ldisc |
740 | * state closed |
741 | */ |
742 | |
743 | static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc) |
744 | { |
745 | struct tty_ldisc *ld = tty_ldisc_get(ldisc); |
746 | |
747 | if (IS_ERR(ld)) |
748 | return -1; |
749 | |
750 | tty_ldisc_close(tty, tty->ldisc); |
751 | tty_ldisc_put(tty->ldisc); |
752 | tty->ldisc = NULL; |
753 | /* |
754 | * Switch the line discipline back |
755 | */ |
756 | tty_ldisc_assign(tty, ld); |
757 | tty_set_termios_ldisc(tty, ldisc); |
758 | |
759 | return 0; |
760 | } |
761 | |
762 | /** |
763 | * tty_ldisc_hangup - hangup ldisc reset |
764 | * @tty: tty being hung up |
765 | * |
766 | * Some tty devices reset their termios when they receive a hangup |
767 | * event. In that situation we must also switch back to N_TTY properly |
768 | * before we reset the termios data. |
769 | * |
770 | * Locking: We can take the ldisc mutex as the rest of the code is |
771 | * careful to allow for this. |
772 | * |
773 | * In the pty pair case this occurs in the close() path of the |
774 | * tty itself so we must be careful about locking rules. |
775 | */ |
776 | |
777 | void tty_ldisc_hangup(struct tty_struct *tty) |
778 | { |
779 | struct tty_ldisc *ld; |
780 | int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS; |
781 | int err = 0; |
782 | |
783 | /* |
784 | * FIXME! What are the locking issues here? This may me overdoing |
785 | * things... This question is especially important now that we've |
786 | * removed the irqlock. |
787 | */ |
788 | ld = tty_ldisc_ref(tty); |
789 | if (ld != NULL) { |
790 | /* We may have no line discipline at this point */ |
791 | if (ld->ops->flush_buffer) |
792 | ld->ops->flush_buffer(tty); |
793 | tty_driver_flush_buffer(tty); |
794 | if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) && |
795 | ld->ops->write_wakeup) |
796 | ld->ops->write_wakeup(tty); |
797 | if (ld->ops->hangup) |
798 | ld->ops->hangup(tty); |
799 | tty_ldisc_deref(ld); |
800 | } |
801 | /* |
802 | * FIXME: Once we trust the LDISC code better we can wait here for |
803 | * ldisc completion and fix the driver call race |
804 | */ |
805 | wake_up_interruptible_poll(&tty->write_wait, POLLOUT); |
806 | wake_up_interruptible_poll(&tty->read_wait, POLLIN); |
807 | /* |
808 | * Shutdown the current line discipline, and reset it to |
809 | * N_TTY if need be. |
810 | * |
811 | * Avoid racing set_ldisc or tty_ldisc_release |
812 | */ |
813 | mutex_lock(&tty->ldisc_mutex); |
814 | |
815 | /* |
816 | * this is like tty_ldisc_halt, but we need to give up |
817 | * the BTM before calling cancel_work_sync, which may |
818 | * need to wait for another function taking the BTM |
819 | */ |
820 | clear_bit(TTY_LDISC, &tty->flags); |
821 | tty_unlock(tty); |
822 | cancel_work_sync(&tty->port->buf.work); |
823 | mutex_unlock(&tty->ldisc_mutex); |
824 | retry: |
825 | tty_lock(tty); |
826 | mutex_lock(&tty->ldisc_mutex); |
827 | |
828 | /* At this point we have a closed ldisc and we want to |
829 | reopen it. We could defer this to the next open but |
830 | it means auditing a lot of other paths so this is |
831 | a FIXME */ |
832 | if (tty->ldisc) { /* Not yet closed */ |
833 | if (atomic_read(&tty->ldisc->users) != 1) { |
834 | char cur_n[TASK_COMM_LEN], tty_n[64]; |
835 | long timeout = 3 * HZ; |
836 | tty_unlock(tty); |
837 | |
838 | while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) { |
839 | timeout = MAX_SCHEDULE_TIMEOUT; |
840 | printk_ratelimited(KERN_WARNING |
841 | "%s: waiting (%s) for %s took too long, but we keep waiting...\n", |
842 | __func__, get_task_comm(cur_n, current), |
843 | tty_name(tty, tty_n)); |
844 | } |
845 | mutex_unlock(&tty->ldisc_mutex); |
846 | goto retry; |
847 | } |
848 | |
849 | if (reset == 0) { |
850 | |
851 | if (!tty_ldisc_reinit(tty, tty->termios.c_line)) |
852 | err = tty_ldisc_open(tty, tty->ldisc); |
853 | else |
854 | err = 1; |
855 | } |
856 | /* If the re-open fails or we reset then go to N_TTY. The |
857 | N_TTY open cannot fail */ |
858 | if (reset || err) { |
859 | BUG_ON(tty_ldisc_reinit(tty, N_TTY)); |
860 | WARN_ON(tty_ldisc_open(tty, tty->ldisc)); |
861 | } |
862 | tty_ldisc_enable(tty); |
863 | } |
864 | mutex_unlock(&tty->ldisc_mutex); |
865 | if (reset) |
866 | tty_reset_termios(tty); |
867 | } |
868 | |
869 | /** |
870 | * tty_ldisc_setup - open line discipline |
871 | * @tty: tty being shut down |
872 | * @o_tty: pair tty for pty/tty pairs |
873 | * |
874 | * Called during the initial open of a tty/pty pair in order to set up the |
875 | * line disciplines and bind them to the tty. This has no locking issues |
876 | * as the device isn't yet active. |
877 | */ |
878 | |
879 | int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty) |
880 | { |
881 | struct tty_ldisc *ld = tty->ldisc; |
882 | int retval; |
883 | |
884 | retval = tty_ldisc_open(tty, ld); |
885 | if (retval) |
886 | return retval; |
887 | |
888 | if (o_tty) { |
889 | retval = tty_ldisc_open(o_tty, o_tty->ldisc); |
890 | if (retval) { |
891 | tty_ldisc_close(tty, ld); |
892 | return retval; |
893 | } |
894 | tty_ldisc_enable(o_tty); |
895 | } |
896 | tty_ldisc_enable(tty); |
897 | return 0; |
898 | } |
899 | |
900 | static void tty_ldisc_kill(struct tty_struct *tty) |
901 | { |
902 | /* There cannot be users from userspace now. But there still might be |
903 | * drivers holding a reference via tty_ldisc_ref. Do not steal them the |
904 | * ldisc until they are done. */ |
905 | tty_ldisc_wait_idle(tty, MAX_SCHEDULE_TIMEOUT); |
906 | |
907 | mutex_lock(&tty->ldisc_mutex); |
908 | /* |
909 | * Now kill off the ldisc |
910 | */ |
911 | tty_ldisc_close(tty, tty->ldisc); |
912 | tty_ldisc_put(tty->ldisc); |
913 | /* Force an oops if we mess this up */ |
914 | tty->ldisc = NULL; |
915 | |
916 | /* Ensure the next open requests the N_TTY ldisc */ |
917 | tty_set_termios_ldisc(tty, N_TTY); |
918 | mutex_unlock(&tty->ldisc_mutex); |
919 | } |
920 | |
921 | /** |
922 | * tty_ldisc_release - release line discipline |
923 | * @tty: tty being shut down |
924 | * @o_tty: pair tty for pty/tty pairs |
925 | * |
926 | * Called during the final close of a tty/pty pair in order to shut down |
927 | * the line discpline layer. On exit the ldisc assigned is N_TTY and the |
928 | * ldisc has not been opened. |
929 | */ |
930 | |
931 | void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty) |
932 | { |
933 | /* |
934 | * Prevent flush_to_ldisc() from rescheduling the work for later. Then |
935 | * kill any delayed work. As this is the final close it does not |
936 | * race with the set_ldisc code path. |
937 | */ |
938 | |
939 | tty_ldisc_halt(tty); |
940 | if (o_tty) |
941 | tty_ldisc_halt(o_tty); |
942 | |
943 | tty_ldisc_flush_works(tty); |
944 | if (o_tty) |
945 | tty_ldisc_flush_works(o_tty); |
946 | |
947 | tty_lock_pair(tty, o_tty); |
948 | /* This will need doing differently if we need to lock */ |
949 | tty_ldisc_kill(tty); |
950 | if (o_tty) |
951 | tty_ldisc_kill(o_tty); |
952 | |
953 | tty_unlock_pair(tty, o_tty); |
954 | /* And the memory resources remaining (buffers, termios) will be |
955 | disposed of when the kref hits zero */ |
956 | } |
957 | |
958 | /** |
959 | * tty_ldisc_init - ldisc setup for new tty |
960 | * @tty: tty being allocated |
961 | * |
962 | * Set up the line discipline objects for a newly allocated tty. Note that |
963 | * the tty structure is not completely set up when this call is made. |
964 | */ |
965 | |
966 | void tty_ldisc_init(struct tty_struct *tty) |
967 | { |
968 | struct tty_ldisc *ld = tty_ldisc_get(N_TTY); |
969 | if (IS_ERR(ld)) |
970 | panic("n_tty: init_tty"); |
971 | tty_ldisc_assign(tty, ld); |
972 | } |
973 | |
974 | /** |
975 | * tty_ldisc_init - ldisc cleanup for new tty |
976 | * @tty: tty that was allocated recently |
977 | * |
978 | * The tty structure must not becompletely set up (tty_ldisc_setup) when |
979 | * this call is made. |
980 | */ |
981 | void tty_ldisc_deinit(struct tty_struct *tty) |
982 | { |
983 | put_ldisc(tty->ldisc); |
984 | tty_ldisc_assign(tty, NULL); |
985 | } |
986 | |
987 | void tty_ldisc_begin(void) |
988 | { |
989 | /* Setup the default TTY line discipline. */ |
990 | (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY); |
991 | } |
992 |
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