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>
7 #include <linux/tty_driver.h>
8 #include <linux/file.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>
22 #undef LDISC_DEBUG_HANGUP
24 #ifdef LDISC_DEBUG_HANGUP
25 #define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
27 #define tty_ldisc_debug(tty, f, args...)
30 /* lockdep nested classes for tty->ldisc_sem */
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.
43 static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
44 /* Line disc dispatch table */
45 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
48 * tty_register_ldisc - install a line discipline
50 * @new_ldisc: pointer to the ldisc object
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.
57 * takes tty_ldiscs_lock to guard against ldisc races
60 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
65 if (disc < N_TTY || disc >= NR_LDISCS)
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);
76 EXPORT_SYMBOL(tty_register_ldisc);
79 * tty_unregister_ldisc - unload a line discipline
81 * @new_ldisc: pointer to the ldisc object
83 * Remove a line discipline from the kernel providing it is not
87 * takes tty_ldiscs_lock to guard against ldisc races
90 int tty_unregister_ldisc(int disc)
95 if (disc < N_TTY || disc >= NR_LDISCS)
98 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
99 if (tty_ldiscs[disc]->refcount)
102 tty_ldiscs[disc] = NULL;
103 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107 EXPORT_SYMBOL(tty_unregister_ldisc);
109 static struct tty_ldisc_ops *get_ldops(int disc)
112 struct tty_ldisc_ops *ldops, *ret;
114 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115 ret = ERR_PTR(-EINVAL);
116 ldops = tty_ldiscs[disc];
118 ret = ERR_PTR(-EAGAIN);
119 if (try_module_get(ldops->owner)) {
124 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
128 static void put_ldops(struct tty_ldisc_ops *ldops)
132 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
134 module_put(ldops->owner);
135 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
139 * tty_ldisc_get - take a reference to an ldisc
140 * @disc: ldisc number
142 * Takes a reference to a line discipline. Deals with refcounts and
143 * module locking counts.
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
149 * -ENOMEM if allocation failure
151 * Otherwise, returns a pointer to the discipline and bumps the
155 * takes tty_ldiscs_lock to guard against ldisc races
158 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
160 struct tty_ldisc *ld;
161 struct tty_ldisc_ops *ldops;
163 if (disc < N_TTY || disc >= NR_LDISCS)
164 return ERR_PTR(-EINVAL);
167 * Get the ldisc ops - we may need to request them to be loaded
168 * dynamically and try again.
170 ldops = get_ldops(disc);
172 request_module("tty-ldisc-%d", disc);
173 ldops = get_ldops(disc);
175 return ERR_CAST(ldops);
178 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
181 return ERR_PTR(-ENOMEM);
191 * tty_ldisc_put - release the ldisc
193 * Complement of tty_ldisc_get().
195 static void tty_ldisc_put(struct tty_ldisc *ld)
197 if (WARN_ON_ONCE(!ld))
204 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
206 return (*pos < NR_LDISCS) ? pos : NULL;
209 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
212 return (*pos < NR_LDISCS) ? pos : NULL;
215 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
219 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
221 int i = *(loff_t *)v;
222 struct tty_ldisc_ops *ldops;
224 ldops = get_ldops(i);
227 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
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,
239 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
241 return seq_open(file, &tty_ldiscs_seq_ops);
244 const struct file_operations tty_ldiscs_proc_fops = {
245 .owner = THIS_MODULE,
246 .open = proc_tty_ldiscs_open,
249 .release = seq_release,
253 * tty_ldisc_ref_wait - wait for the tty ldisc
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.
260 * Returns: NULL if the tty has been hungup and not re-opened with
261 * a new file descriptor, otherwise valid ldisc reference
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)
268 * Note: a file_operations routine (read/poll/write) should use this
269 * function to wait for any ldisc lifetime events to finish.
272 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
274 struct tty_ldisc *ld;
276 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
279 ldsem_up_read(&tty->ldisc_sem);
282 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
285 * tty_ldisc_ref - get the tty ldisc
288 * Dereference the line discipline for the terminal and take a
289 * reference to it. If the line discipline is in flux then
290 * return NULL. Can be called from IRQ and timer functions.
293 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
295 struct tty_ldisc *ld = NULL;
297 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
300 ldsem_up_read(&tty->ldisc_sem);
304 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
307 * tty_ldisc_deref - free a tty ldisc reference
308 * @ld: reference to free up
310 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
311 * be called in IRQ context.
314 void tty_ldisc_deref(struct tty_ldisc *ld)
316 ldsem_up_read(&ld->tty->ldisc_sem);
318 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
322 __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
324 return ldsem_down_write(&tty->ldisc_sem, timeout);
328 __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
330 return ldsem_down_write_nested(&tty->ldisc_sem,
331 LDISC_SEM_OTHER, timeout);
334 static inline void __tty_ldisc_unlock(struct tty_struct *tty)
336 ldsem_up_write(&tty->ldisc_sem);
339 static int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
343 ret = __tty_ldisc_lock(tty, timeout);
346 set_bit(TTY_LDISC_HALTED, &tty->flags);
350 static void tty_ldisc_unlock(struct tty_struct *tty)
352 clear_bit(TTY_LDISC_HALTED, &tty->flags);
353 __tty_ldisc_unlock(tty);
357 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
358 unsigned long timeout)
363 ret = __tty_ldisc_lock(tty, timeout);
365 ret = __tty_ldisc_lock_nested(tty2, timeout);
367 __tty_ldisc_unlock(tty);
370 /* if this is possible, it has lots of implications */
371 WARN_ON_ONCE(tty == tty2);
372 if (tty2 && tty != tty2) {
373 ret = __tty_ldisc_lock(tty2, timeout);
375 ret = __tty_ldisc_lock_nested(tty, timeout);
377 __tty_ldisc_unlock(tty2);
380 ret = __tty_ldisc_lock(tty, timeout);
386 set_bit(TTY_LDISC_HALTED, &tty->flags);
388 set_bit(TTY_LDISC_HALTED, &tty2->flags);
392 static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
394 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
397 static void tty_ldisc_unlock_pair(struct tty_struct *tty,
398 struct tty_struct *tty2)
400 __tty_ldisc_unlock(tty);
402 __tty_ldisc_unlock(tty2);
406 * tty_ldisc_flush - flush line discipline queue
409 * Flush the line discipline queue (if any) and the tty flip buffers
413 void tty_ldisc_flush(struct tty_struct *tty)
415 struct tty_ldisc *ld = tty_ldisc_ref(tty);
417 tty_buffer_flush(tty, ld);
421 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
424 * tty_set_termios_ldisc - set ldisc field
425 * @tty: tty structure
426 * @disc: line discipline number
428 * This is probably overkill for real world processors but
429 * they are not on hot paths so a little discipline won't do
432 * The line discipline-related tty_struct fields are reset to
433 * prevent the ldisc driver from re-using stale information for
434 * the new ldisc instance.
436 * Locking: takes termios_rwsem
439 static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
441 down_write(&tty->termios_rwsem);
442 tty->termios.c_line = disc;
443 up_write(&tty->termios_rwsem);
445 tty->disc_data = NULL;
446 tty->receive_room = 0;
450 * tty_ldisc_open - open a line discipline
451 * @tty: tty we are opening the ldisc on
452 * @ld: discipline to open
454 * A helper opening method. Also a convenient debugging and check
457 * Locking: always called with BTM already held.
460 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
462 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
465 /* BTM here locks versus a hangup event */
466 ret = ld->ops->open(tty);
468 clear_bit(TTY_LDISC_OPEN, &tty->flags);
470 tty_ldisc_debug(tty, "%p: opened\n", ld);
477 * tty_ldisc_close - close a line discipline
478 * @tty: tty we are opening the ldisc on
479 * @ld: discipline to close
481 * A helper close method. Also a convenient debugging and check
485 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
487 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
488 clear_bit(TTY_LDISC_OPEN, &tty->flags);
491 tty_ldisc_debug(tty, "%p: closed\n", ld);
495 * tty_set_ldisc - set line discipline
496 * @tty: the terminal to set
497 * @ldisc: the line discipline
499 * Set the discipline of a tty line. Must be called from a process
500 * context. The ldisc change logic has to protect itself against any
501 * overlapping ldisc change (including on the other end of pty pairs),
502 * the close of one side of a tty/pty pair, and eventually hangup.
505 int tty_set_ldisc(struct tty_struct *tty, int disc)
507 int retval, old_disc;
510 retval = tty_ldisc_lock(tty, 5 * HZ);
519 /* Check the no-op case */
520 old_disc = tty->ldisc->ops->num;
521 if (old_disc == disc)
524 if (test_bit(TTY_HUPPED, &tty->flags)) {
525 /* We were raced by hangup */
530 retval = tty_ldisc_reinit(tty, disc);
532 /* Back to the old one or N_TTY if we can't */
533 if (tty_ldisc_reinit(tty, old_disc) < 0) {
534 pr_err("tty: TIOCSETD failed, reinitializing N_TTY\n");
535 if (tty_ldisc_reinit(tty, N_TTY) < 0) {
536 /* At this point we have tty->ldisc == NULL. */
537 pr_err("tty: reinitializing N_TTY failed\n");
542 if (tty->ldisc && tty->ldisc->ops->num != old_disc &&
543 tty->ops->set_ldisc) {
544 down_read(&tty->termios_rwsem);
545 tty->ops->set_ldisc(tty);
546 up_read(&tty->termios_rwsem);
550 tty_ldisc_unlock(tty);
552 /* Restart the work queue in case no characters kick it off. Safe if
554 tty_buffer_restart_work(tty->port);
561 * tty_ldisc_kill - teardown ldisc
562 * @tty: tty being released
564 * Perform final close of the ldisc and reset tty->ldisc
566 static void tty_ldisc_kill(struct tty_struct *tty)
571 * Now kill off the ldisc
573 tty_ldisc_close(tty, tty->ldisc);
574 tty_ldisc_put(tty->ldisc);
575 /* Force an oops if we mess this up */
580 * tty_reset_termios - reset terminal state
583 * Restore a terminal to the driver default state.
586 static void tty_reset_termios(struct tty_struct *tty)
588 down_write(&tty->termios_rwsem);
589 tty->termios = tty->driver->init_termios;
590 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
591 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
592 up_write(&tty->termios_rwsem);
597 * tty_ldisc_reinit - reinitialise the tty ldisc
598 * @tty: tty to reinit
599 * @disc: line discipline to reinitialize
601 * Completely reinitialize the line discipline state, by closing the
602 * current instance, if there is one, and opening a new instance. If
603 * an error occurs opening the new non-N_TTY instance, the instance
604 * is dropped and tty->ldisc reset to NULL. The caller can then retry
605 * with N_TTY instead.
607 * Returns 0 if successful, otherwise error code < 0
610 int tty_ldisc_reinit(struct tty_struct *tty, int disc)
612 struct tty_ldisc *ld;
615 ld = tty_ldisc_get(tty, disc);
620 tty_ldisc_close(tty, tty->ldisc);
621 tty_ldisc_put(tty->ldisc);
624 /* switch the line discipline */
626 tty_set_termios_ldisc(tty, disc);
627 retval = tty_ldisc_open(tty, tty->ldisc);
629 tty_ldisc_put(tty->ldisc);
636 * tty_ldisc_hangup - hangup ldisc reset
637 * @tty: tty being hung up
639 * Some tty devices reset their termios when they receive a hangup
640 * event. In that situation we must also switch back to N_TTY properly
641 * before we reset the termios data.
643 * Locking: We can take the ldisc mutex as the rest of the code is
644 * careful to allow for this.
646 * In the pty pair case this occurs in the close() path of the
647 * tty itself so we must be careful about locking rules.
650 void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
652 struct tty_ldisc *ld;
654 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
656 ld = tty_ldisc_ref(tty);
658 if (ld->ops->flush_buffer)
659 ld->ops->flush_buffer(tty);
660 tty_driver_flush_buffer(tty);
661 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
662 ld->ops->write_wakeup)
663 ld->ops->write_wakeup(tty);
665 ld->ops->hangup(tty);
669 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
670 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
673 * Shutdown the current line discipline, and reset it to
676 * Avoid racing set_ldisc or tty_ldisc_release
678 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
680 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
681 tty_reset_termios(tty);
685 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0)
686 tty_ldisc_reinit(tty, N_TTY);
690 tty_ldisc_unlock(tty);
694 * tty_ldisc_setup - open line discipline
695 * @tty: tty being shut down
696 * @o_tty: pair tty for pty/tty pairs
698 * Called during the initial open of a tty/pty pair in order to set up the
699 * line disciplines and bind them to the tty. This has no locking issues
700 * as the device isn't yet active.
703 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
705 int retval = tty_ldisc_open(tty, tty->ldisc);
710 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
712 tty_ldisc_close(tty, tty->ldisc);
720 * tty_ldisc_release - release line discipline
721 * @tty: tty being shut down (or one end of pty pair)
723 * Called during the final close of a tty or a pty pair in order to shut
724 * down the line discpline layer. On exit, each tty's ldisc is NULL.
727 void tty_ldisc_release(struct tty_struct *tty)
729 struct tty_struct *o_tty = tty->link;
732 * Shutdown this line discipline. As this is the final close,
733 * it does not race with the set_ldisc code path.
736 tty_ldisc_lock_pair(tty, o_tty);
739 tty_ldisc_kill(o_tty);
740 tty_ldisc_unlock_pair(tty, o_tty);
742 /* And the memory resources remaining (buffers, termios) will be
743 disposed of when the kref hits zero */
745 tty_ldisc_debug(tty, "released\n");
749 * tty_ldisc_init - ldisc setup for new tty
750 * @tty: tty being allocated
752 * Set up the line discipline objects for a newly allocated tty. Note that
753 * the tty structure is not completely set up when this call is made.
756 void tty_ldisc_init(struct tty_struct *tty)
758 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
760 panic("n_tty: init_tty");
765 * tty_ldisc_deinit - ldisc cleanup for new tty
766 * @tty: tty that was allocated recently
768 * The tty structure must not becompletely set up (tty_ldisc_setup) when
771 void tty_ldisc_deinit(struct tty_struct *tty)
774 tty_ldisc_put(tty->ldisc);