Version:  2.0.40 2.2.26 2.4.37 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6

Linux/drivers/tty/tty_ldisc.c

  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/module.h>
 15 #include <linux/device.h>
 16 #include <linux/wait.h>
 17 #include <linux/bitops.h>
 18 #include <linux/seq_file.h>
 19 #include <linux/uaccess.h>
 20 #include <linux/ratelimit.h>
 21 
 22 #undef LDISC_DEBUG_HANGUP
 23 
 24 #ifdef LDISC_DEBUG_HANGUP
 25 #define tty_ldisc_debug(tty, f, args...)        tty_debug(tty, f, ##args)
 26 #else
 27 #define tty_ldisc_debug(tty, f, args...)
 28 #endif
 29 
 30 /* lockdep nested classes for tty->ldisc_sem */
 31 enum {
 32         LDISC_SEM_NORMAL,
 33         LDISC_SEM_OTHER,
 34 };
 35 
 36 
 37 /*
 38  *      This guards the refcounted line discipline lists. The lock
 39  *      must be taken with irqs off because there are hangup path
 40  *      callers who will do ldisc lookups and cannot sleep.
 41  */
 42 
 43 static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
 44 /* Line disc dispatch table */
 45 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
 46 
 47 /**
 48  *      tty_register_ldisc      -       install a line discipline
 49  *      @disc: ldisc number
 50  *      @new_ldisc: pointer to the ldisc object
 51  *
 52  *      Installs a new line discipline into the kernel. The discipline
 53  *      is set up as unreferenced and then made available to the kernel
 54  *      from this point onwards.
 55  *
 56  *      Locking:
 57  *              takes tty_ldiscs_lock to guard against ldisc races
 58  */
 59 
 60 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
 61 {
 62         unsigned long flags;
 63         int ret = 0;
 64 
 65         if (disc < N_TTY || disc >= NR_LDISCS)
 66                 return -EINVAL;
 67 
 68         raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
 69         tty_ldiscs[disc] = new_ldisc;
 70         new_ldisc->num = disc;
 71         new_ldisc->refcount = 0;
 72         raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
 73 
 74         return ret;
 75 }
 76 EXPORT_SYMBOL(tty_register_ldisc);
 77 
 78 /**
 79  *      tty_unregister_ldisc    -       unload a line discipline
 80  *      @disc: ldisc number
 81  *      @new_ldisc: pointer to the ldisc object
 82  *
 83  *      Remove a line discipline from the kernel providing it is not
 84  *      currently in use.
 85  *
 86  *      Locking:
 87  *              takes tty_ldiscs_lock to guard against ldisc races
 88  */
 89 
 90 int tty_unregister_ldisc(int disc)
 91 {
 92         unsigned long flags;
 93         int ret = 0;
 94 
 95         if (disc < N_TTY || disc >= NR_LDISCS)
 96                 return -EINVAL;
 97 
 98         raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
 99         if (tty_ldiscs[disc]->refcount)
100                 ret = -EBUSY;
101         else
102                 tty_ldiscs[disc] = NULL;
103         raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
104 
105         return ret;
106 }
107 EXPORT_SYMBOL(tty_unregister_ldisc);
108 
109 static struct tty_ldisc_ops *get_ldops(int disc)
110 {
111         unsigned long flags;
112         struct tty_ldisc_ops *ldops, *ret;
113 
114         raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115         ret = ERR_PTR(-EINVAL);
116         ldops = tty_ldiscs[disc];
117         if (ldops) {
118                 ret = ERR_PTR(-EAGAIN);
119                 if (try_module_get(ldops->owner)) {
120                         ldops->refcount++;
121                         ret = ldops;
122                 }
123         }
124         raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
125         return ret;
126 }
127 
128 static void put_ldops(struct tty_ldisc_ops *ldops)
129 {
130         unsigned long flags;
131 
132         raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
133         ldops->refcount--;
134         module_put(ldops->owner);
135         raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
136 }
137 
138 /**
139  *      tty_ldisc_get           -       take a reference to an ldisc
140  *      @disc: ldisc number
141  *
142  *      Takes a reference to a line discipline. Deals with refcounts and
143  *      module locking counts.
144  *
145  *      Returns: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
146  *                       if the discipline is not registered
147  *               -EAGAIN if request_module() failed to load or register the
148  *                       the discipline
149  *               -ENOMEM if allocation failure
150  *
151  *               Otherwise, returns a pointer to the discipline and bumps the
152  *               ref count
153  *
154  *      Locking:
155  *              takes tty_ldiscs_lock to guard against ldisc races
156  */
157 
158 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
159 {
160         struct tty_ldisc *ld;
161         struct tty_ldisc_ops *ldops;
162 
163         if (disc < N_TTY || disc >= NR_LDISCS)
164                 return ERR_PTR(-EINVAL);
165 
166         /*
167          * Get the ldisc ops - we may need to request them to be loaded
168          * dynamically and try again.
169          */
170         ldops = get_ldops(disc);
171         if (IS_ERR(ldops)) {
172                 request_module("tty-ldisc-%d", disc);
173                 ldops = get_ldops(disc);
174                 if (IS_ERR(ldops))
175                         return ERR_CAST(ldops);
176         }
177 
178         ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
179         if (ld == NULL) {
180                 put_ldops(ldops);
181                 return ERR_PTR(-ENOMEM);
182         }
183 
184         ld->ops = ldops;
185         ld->tty = tty;
186 
187         return ld;
188 }
189 
190 /**
191  *      tty_ldisc_put           -       release the ldisc
192  *
193  *      Complement of tty_ldisc_get().
194  */
195 static void tty_ldisc_put(struct tty_ldisc *ld)
196 {
197         if (WARN_ON_ONCE(!ld))
198                 return;
199 
200         put_ldops(ld->ops);
201         kfree(ld);
202 }
203 
204 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
205 {
206         return (*pos < NR_LDISCS) ? pos : NULL;
207 }
208 
209 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
210 {
211         (*pos)++;
212         return (*pos < NR_LDISCS) ? pos : NULL;
213 }
214 
215 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
216 {
217 }
218 
219 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
220 {
221         int i = *(loff_t *)v;
222         struct tty_ldisc_ops *ldops;
223 
224         ldops = get_ldops(i);
225         if (IS_ERR(ldops))
226                 return 0;
227         seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
228         put_ldops(ldops);
229         return 0;
230 }
231 
232 static const struct seq_operations tty_ldiscs_seq_ops = {
233         .start  = tty_ldiscs_seq_start,
234         .next   = tty_ldiscs_seq_next,
235         .stop   = tty_ldiscs_seq_stop,
236         .show   = tty_ldiscs_seq_show,
237 };
238 
239 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
240 {
241         return seq_open(file, &tty_ldiscs_seq_ops);
242 }
243 
244 const struct file_operations tty_ldiscs_proc_fops = {
245         .owner          = THIS_MODULE,
246         .open           = proc_tty_ldiscs_open,
247         .read           = seq_read,
248         .llseek         = seq_lseek,
249         .release        = seq_release,
250 };
251 
252 /**
253  *      tty_ldisc_ref_wait      -       wait for the tty ldisc
254  *      @tty: tty device
255  *
256  *      Dereference the line discipline for the terminal and take a
257  *      reference to it. If the line discipline is in flux then
258  *      wait patiently until it changes.
259  *
260  *      Returns: NULL if the tty has been hungup and not re-opened with
261  *               a new file descriptor, otherwise valid ldisc reference
262  *
263  *      Note: Must not be called from an IRQ/timer context. The caller
264  *      must also be careful not to hold other locks that will deadlock
265  *      against a discipline change, such as an existing ldisc reference
266  *      (which we check for)
267  *
268  *      Note: a file_operations routine (read/poll/write) should use this
269  *      function to wait for any ldisc lifetime events to finish.
270  */
271 
272 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
273 {
274         ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
275         if (!tty->ldisc)
276                 ldsem_up_read(&tty->ldisc_sem);
277         return tty->ldisc;
278 }
279 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
280 
281 /**
282  *      tty_ldisc_ref           -       get the tty ldisc
283  *      @tty: tty device
284  *
285  *      Dereference the line discipline for the terminal and take a
286  *      reference to it. If the line discipline is in flux then
287  *      return NULL. Can be called from IRQ and timer functions.
288  */
289 
290 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
291 {
292         struct tty_ldisc *ld = NULL;
293 
294         if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
295                 ld = tty->ldisc;
296                 if (!ld)
297                         ldsem_up_read(&tty->ldisc_sem);
298         }
299         return ld;
300 }
301 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
302 
303 /**
304  *      tty_ldisc_deref         -       free a tty ldisc reference
305  *      @ld: reference to free up
306  *
307  *      Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
308  *      be called in IRQ context.
309  */
310 
311 void tty_ldisc_deref(struct tty_ldisc *ld)
312 {
313         ldsem_up_read(&ld->tty->ldisc_sem);
314 }
315 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
316 
317 
318 static inline int
319 __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
320 {
321         return ldsem_down_write(&tty->ldisc_sem, timeout);
322 }
323 
324 static inline int
325 __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
326 {
327         return ldsem_down_write_nested(&tty->ldisc_sem,
328                                        LDISC_SEM_OTHER, timeout);
329 }
330 
331 static inline void __tty_ldisc_unlock(struct tty_struct *tty)
332 {
333         ldsem_up_write(&tty->ldisc_sem);
334 }
335 
336 static int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
337 {
338         int ret;
339 
340         ret = __tty_ldisc_lock(tty, timeout);
341         if (!ret)
342                 return -EBUSY;
343         set_bit(TTY_LDISC_HALTED, &tty->flags);
344         return 0;
345 }
346 
347 static void tty_ldisc_unlock(struct tty_struct *tty)
348 {
349         clear_bit(TTY_LDISC_HALTED, &tty->flags);
350         __tty_ldisc_unlock(tty);
351 }
352 
353 static int
354 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
355                             unsigned long timeout)
356 {
357         int ret;
358 
359         if (tty < tty2) {
360                 ret = __tty_ldisc_lock(tty, timeout);
361                 if (ret) {
362                         ret = __tty_ldisc_lock_nested(tty2, timeout);
363                         if (!ret)
364                                 __tty_ldisc_unlock(tty);
365                 }
366         } else {
367                 /* if this is possible, it has lots of implications */
368                 WARN_ON_ONCE(tty == tty2);
369                 if (tty2 && tty != tty2) {
370                         ret = __tty_ldisc_lock(tty2, timeout);
371                         if (ret) {
372                                 ret = __tty_ldisc_lock_nested(tty, timeout);
373                                 if (!ret)
374                                         __tty_ldisc_unlock(tty2);
375                         }
376                 } else
377                         ret = __tty_ldisc_lock(tty, timeout);
378         }
379 
380         if (!ret)
381                 return -EBUSY;
382 
383         set_bit(TTY_LDISC_HALTED, &tty->flags);
384         if (tty2)
385                 set_bit(TTY_LDISC_HALTED, &tty2->flags);
386         return 0;
387 }
388 
389 static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
390 {
391         tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
392 }
393 
394 static void tty_ldisc_unlock_pair(struct tty_struct *tty,
395                                   struct tty_struct *tty2)
396 {
397         __tty_ldisc_unlock(tty);
398         if (tty2)
399                 __tty_ldisc_unlock(tty2);
400 }
401 
402 /**
403  *      tty_ldisc_flush -       flush line discipline queue
404  *      @tty: tty
405  *
406  *      Flush the line discipline queue (if any) and the tty flip buffers
407  *      for this tty.
408  */
409 
410 void tty_ldisc_flush(struct tty_struct *tty)
411 {
412         struct tty_ldisc *ld = tty_ldisc_ref(tty);
413 
414         tty_buffer_flush(tty, ld);
415         if (ld)
416                 tty_ldisc_deref(ld);
417 }
418 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
419 
420 /**
421  *      tty_set_termios_ldisc           -       set ldisc field
422  *      @tty: tty structure
423  *      @disc: line discipline number
424  *
425  *      This is probably overkill for real world processors but
426  *      they are not on hot paths so a little discipline won't do
427  *      any harm.
428  *
429  *      The line discipline-related tty_struct fields are reset to
430  *      prevent the ldisc driver from re-using stale information for
431  *      the new ldisc instance.
432  *
433  *      Locking: takes termios_rwsem
434  */
435 
436 static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
437 {
438         down_write(&tty->termios_rwsem);
439         tty->termios.c_line = disc;
440         up_write(&tty->termios_rwsem);
441 
442         tty->disc_data = NULL;
443         tty->receive_room = 0;
444 }
445 
446 /**
447  *      tty_ldisc_open          -       open a line discipline
448  *      @tty: tty we are opening the ldisc on
449  *      @ld: discipline to open
450  *
451  *      A helper opening method. Also a convenient debugging and check
452  *      point.
453  *
454  *      Locking: always called with BTM already held.
455  */
456 
457 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
458 {
459         WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
460         if (ld->ops->open) {
461                 int ret;
462                 /* BTM here locks versus a hangup event */
463                 ret = ld->ops->open(tty);
464                 if (ret)
465                         clear_bit(TTY_LDISC_OPEN, &tty->flags);
466 
467                 tty_ldisc_debug(tty, "%p: opened\n", ld);
468                 return ret;
469         }
470         return 0;
471 }
472 
473 /**
474  *      tty_ldisc_close         -       close a line discipline
475  *      @tty: tty we are opening the ldisc on
476  *      @ld: discipline to close
477  *
478  *      A helper close method. Also a convenient debugging and check
479  *      point.
480  */
481 
482 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
483 {
484         WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
485         clear_bit(TTY_LDISC_OPEN, &tty->flags);
486         if (ld->ops->close)
487                 ld->ops->close(tty);
488         tty_ldisc_debug(tty, "%p: closed\n", ld);
489 }
490 
491 /**
492  *      tty_ldisc_restore       -       helper for tty ldisc change
493  *      @tty: tty to recover
494  *      @old: previous ldisc
495  *
496  *      Restore the previous line discipline or N_TTY when a line discipline
497  *      change fails due to an open error
498  */
499 
500 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
501 {
502         struct tty_ldisc *new_ldisc;
503         int r;
504 
505         /* There is an outstanding reference here so this is safe */
506         old = tty_ldisc_get(tty, old->ops->num);
507         WARN_ON(IS_ERR(old));
508         tty->ldisc = old;
509         tty_set_termios_ldisc(tty, old->ops->num);
510         if (tty_ldisc_open(tty, old) < 0) {
511                 tty_ldisc_put(old);
512                 /* This driver is always present */
513                 new_ldisc = tty_ldisc_get(tty, N_TTY);
514                 if (IS_ERR(new_ldisc))
515                         panic("n_tty: get");
516                 tty->ldisc = new_ldisc;
517                 tty_set_termios_ldisc(tty, N_TTY);
518                 r = tty_ldisc_open(tty, new_ldisc);
519                 if (r < 0)
520                         panic("Couldn't open N_TTY ldisc for "
521                               "%s --- error %d.",
522                               tty_name(tty), r);
523         }
524 }
525 
526 /**
527  *      tty_set_ldisc           -       set line discipline
528  *      @tty: the terminal to set
529  *      @ldisc: the line discipline
530  *
531  *      Set the discipline of a tty line. Must be called from a process
532  *      context. The ldisc change logic has to protect itself against any
533  *      overlapping ldisc change (including on the other end of pty pairs),
534  *      the close of one side of a tty/pty pair, and eventually hangup.
535  */
536 
537 int tty_set_ldisc(struct tty_struct *tty, int disc)
538 {
539         int retval;
540         struct tty_ldisc *old_ldisc, *new_ldisc;
541 
542         new_ldisc = tty_ldisc_get(tty, disc);
543         if (IS_ERR(new_ldisc))
544                 return PTR_ERR(new_ldisc);
545 
546         tty_lock(tty);
547         retval = tty_ldisc_lock(tty, 5 * HZ);
548         if (retval)
549                 goto err;
550 
551         if (!tty->ldisc) {
552                 retval = -EIO;
553                 goto out;
554         }
555 
556         /* Check the no-op case */
557         if (tty->ldisc->ops->num == disc)
558                 goto out;
559 
560         if (test_bit(TTY_HUPPED, &tty->flags)) {
561                 /* We were raced by hangup */
562                 retval = -EIO;
563                 goto out;
564         }
565 
566         old_ldisc = tty->ldisc;
567 
568         /* Shutdown the old discipline. */
569         tty_ldisc_close(tty, old_ldisc);
570 
571         /* Now set up the new line discipline. */
572         tty->ldisc = new_ldisc;
573         tty_set_termios_ldisc(tty, disc);
574 
575         retval = tty_ldisc_open(tty, new_ldisc);
576         if (retval < 0) {
577                 /* Back to the old one or N_TTY if we can't */
578                 tty_ldisc_put(new_ldisc);
579                 tty_ldisc_restore(tty, old_ldisc);
580         }
581 
582         if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
583                 down_read(&tty->termios_rwsem);
584                 tty->ops->set_ldisc(tty);
585                 up_read(&tty->termios_rwsem);
586         }
587 
588         /* At this point we hold a reference to the new ldisc and a
589            reference to the old ldisc, or we hold two references to
590            the old ldisc (if it was restored as part of error cleanup
591            above). In either case, releasing a single reference from
592            the old ldisc is correct. */
593         new_ldisc = old_ldisc;
594 out:
595         tty_ldisc_unlock(tty);
596 
597         /* Restart the work queue in case no characters kick it off. Safe if
598            already running */
599         tty_buffer_restart_work(tty->port);
600 err:
601         tty_ldisc_put(new_ldisc);       /* drop the extra reference */
602         tty_unlock(tty);
603         return retval;
604 }
605 
606 /**
607  *      tty_ldisc_kill  -       teardown ldisc
608  *      @tty: tty being released
609  *
610  *      Perform final close of the ldisc and reset tty->ldisc
611  */
612 static void tty_ldisc_kill(struct tty_struct *tty)
613 {
614         if (!tty->ldisc)
615                 return;
616         /*
617          * Now kill off the ldisc
618          */
619         tty_ldisc_close(tty, tty->ldisc);
620         tty_ldisc_put(tty->ldisc);
621         /* Force an oops if we mess this up */
622         tty->ldisc = NULL;
623 }
624 
625 /**
626  *      tty_reset_termios       -       reset terminal state
627  *      @tty: tty to reset
628  *
629  *      Restore a terminal to the driver default state.
630  */
631 
632 static void tty_reset_termios(struct tty_struct *tty)
633 {
634         down_write(&tty->termios_rwsem);
635         tty->termios = tty->driver->init_termios;
636         tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
637         tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
638         up_write(&tty->termios_rwsem);
639 }
640 
641 
642 /**
643  *      tty_ldisc_reinit        -       reinitialise the tty ldisc
644  *      @tty: tty to reinit
645  *      @disc: line discipline to reinitialize
646  *
647  *      Completely reinitialize the line discipline state, by closing the
648  *      current instance, if there is one, and opening a new instance. If
649  *      an error occurs opening the new non-N_TTY instance, the instance
650  *      is dropped and tty->ldisc reset to NULL. The caller can then retry
651  *      with N_TTY instead.
652  *
653  *      Returns 0 if successful, otherwise error code < 0
654  */
655 
656 int tty_ldisc_reinit(struct tty_struct *tty, int disc)
657 {
658         struct tty_ldisc *ld;
659         int retval;
660 
661         ld = tty_ldisc_get(tty, disc);
662         if (IS_ERR(ld)) {
663                 BUG_ON(disc == N_TTY);
664                 return PTR_ERR(ld);
665         }
666 
667         if (tty->ldisc) {
668                 tty_ldisc_close(tty, tty->ldisc);
669                 tty_ldisc_put(tty->ldisc);
670         }
671 
672         /* switch the line discipline */
673         tty->ldisc = ld;
674         tty_set_termios_ldisc(tty, disc);
675         retval = tty_ldisc_open(tty, tty->ldisc);
676         if (retval) {
677                 if (!WARN_ON(disc == N_TTY)) {
678                         tty_ldisc_put(tty->ldisc);
679                         tty->ldisc = NULL;
680                 }
681         }
682         return retval;
683 }
684 
685 /**
686  *      tty_ldisc_hangup                -       hangup ldisc reset
687  *      @tty: tty being hung up
688  *
689  *      Some tty devices reset their termios when they receive a hangup
690  *      event. In that situation we must also switch back to N_TTY properly
691  *      before we reset the termios data.
692  *
693  *      Locking: We can take the ldisc mutex as the rest of the code is
694  *      careful to allow for this.
695  *
696  *      In the pty pair case this occurs in the close() path of the
697  *      tty itself so we must be careful about locking rules.
698  */
699 
700 void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
701 {
702         struct tty_ldisc *ld;
703 
704         tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
705 
706         ld = tty_ldisc_ref(tty);
707         if (ld != NULL) {
708                 if (ld->ops->flush_buffer)
709                         ld->ops->flush_buffer(tty);
710                 tty_driver_flush_buffer(tty);
711                 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
712                     ld->ops->write_wakeup)
713                         ld->ops->write_wakeup(tty);
714                 if (ld->ops->hangup)
715                         ld->ops->hangup(tty);
716                 tty_ldisc_deref(ld);
717         }
718 
719         wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
720         wake_up_interruptible_poll(&tty->read_wait, POLLIN);
721 
722         /*
723          * Shutdown the current line discipline, and reset it to
724          * N_TTY if need be.
725          *
726          * Avoid racing set_ldisc or tty_ldisc_release
727          */
728         tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
729 
730         if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
731                 tty_reset_termios(tty);
732 
733         if (tty->ldisc) {
734                 if (reinit) {
735                         if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0)
736                                 tty_ldisc_reinit(tty, N_TTY);
737                 } else
738                         tty_ldisc_kill(tty);
739         }
740         tty_ldisc_unlock(tty);
741 }
742 
743 /**
744  *      tty_ldisc_setup                 -       open line discipline
745  *      @tty: tty being shut down
746  *      @o_tty: pair tty for pty/tty pairs
747  *
748  *      Called during the initial open of a tty/pty pair in order to set up the
749  *      line disciplines and bind them to the tty. This has no locking issues
750  *      as the device isn't yet active.
751  */
752 
753 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
754 {
755         int retval = tty_ldisc_open(tty, tty->ldisc);
756         if (retval)
757                 return retval;
758 
759         if (o_tty) {
760                 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
761                 if (retval) {
762                         tty_ldisc_close(tty, tty->ldisc);
763                         return retval;
764                 }
765         }
766         return 0;
767 }
768 
769 /**
770  *      tty_ldisc_release               -       release line discipline
771  *      @tty: tty being shut down (or one end of pty pair)
772  *
773  *      Called during the final close of a tty or a pty pair in order to shut
774  *      down the line discpline layer. On exit, each tty's ldisc is NULL.
775  */
776 
777 void tty_ldisc_release(struct tty_struct *tty)
778 {
779         struct tty_struct *o_tty = tty->link;
780 
781         /*
782          * Shutdown this line discipline. As this is the final close,
783          * it does not race with the set_ldisc code path.
784          */
785 
786         tty_ldisc_lock_pair(tty, o_tty);
787         tty_ldisc_kill(tty);
788         if (o_tty)
789                 tty_ldisc_kill(o_tty);
790         tty_ldisc_unlock_pair(tty, o_tty);
791 
792         /* And the memory resources remaining (buffers, termios) will be
793            disposed of when the kref hits zero */
794 
795         tty_ldisc_debug(tty, "released\n");
796 }
797 
798 /**
799  *      tty_ldisc_init          -       ldisc setup for new tty
800  *      @tty: tty being allocated
801  *
802  *      Set up the line discipline objects for a newly allocated tty. Note that
803  *      the tty structure is not completely set up when this call is made.
804  */
805 
806 void tty_ldisc_init(struct tty_struct *tty)
807 {
808         struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
809         if (IS_ERR(ld))
810                 panic("n_tty: init_tty");
811         tty->ldisc = ld;
812 }
813 
814 /**
815  *      tty_ldisc_deinit        -       ldisc cleanup for new tty
816  *      @tty: tty that was allocated recently
817  *
818  *      The tty structure must not becompletely set up (tty_ldisc_setup) when
819  *      this call is made.
820  */
821 void tty_ldisc_deinit(struct tty_struct *tty)
822 {
823         if (tty->ldisc)
824                 tty_ldisc_put(tty->ldisc);
825         tty->ldisc = NULL;
826 }
827 

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