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