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/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>
23 #undef LDISC_DEBUG_HANGUP
25 #ifdef LDISC_DEBUG_HANGUP
26 #define tty_ldisc_debug(tty, f, args...) ({ \
28 printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
31 #define tty_ldisc_debug(tty, f, args...)
34 /* lockdep nested classes for tty->ldisc_sem */
42 * This guards the refcounted line discipline lists. The lock
43 * must be taken with irqs off because there are hangup path
44 * callers who will do ldisc lookups and cannot sleep.
47 static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
48 /* Line disc dispatch table */
49 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
52 * tty_register_ldisc - install a line discipline
54 * @new_ldisc: pointer to the ldisc object
56 * Installs a new line discipline into the kernel. The discipline
57 * is set up as unreferenced and then made available to the kernel
58 * from this point onwards.
61 * takes tty_ldiscs_lock to guard against ldisc races
64 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
69 if (disc < N_TTY || disc >= NR_LDISCS)
72 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
73 tty_ldiscs[disc] = new_ldisc;
74 new_ldisc->num = disc;
75 new_ldisc->refcount = 0;
76 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
80 EXPORT_SYMBOL(tty_register_ldisc);
83 * tty_unregister_ldisc - unload a line discipline
85 * @new_ldisc: pointer to the ldisc object
87 * Remove a line discipline from the kernel providing it is not
91 * takes tty_ldiscs_lock to guard against ldisc races
94 int tty_unregister_ldisc(int disc)
99 if (disc < N_TTY || disc >= NR_LDISCS)
102 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
103 if (tty_ldiscs[disc]->refcount)
106 tty_ldiscs[disc] = NULL;
107 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
111 EXPORT_SYMBOL(tty_unregister_ldisc);
113 static struct tty_ldisc_ops *get_ldops(int disc)
116 struct tty_ldisc_ops *ldops, *ret;
118 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
119 ret = ERR_PTR(-EINVAL);
120 ldops = tty_ldiscs[disc];
122 ret = ERR_PTR(-EAGAIN);
123 if (try_module_get(ldops->owner)) {
128 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
132 static void put_ldops(struct tty_ldisc_ops *ldops)
136 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
138 module_put(ldops->owner);
139 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
143 * tty_ldisc_get - take a reference to an ldisc
144 * @disc: ldisc number
146 * Takes a reference to a line discipline. Deals with refcounts and
147 * module locking counts. Returns NULL if the discipline is not available.
148 * Returns a pointer to the discipline and bumps the ref count if it is
152 * takes tty_ldiscs_lock to guard against ldisc races
155 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
157 struct tty_ldisc *ld;
158 struct tty_ldisc_ops *ldops;
160 if (disc < N_TTY || disc >= NR_LDISCS)
161 return ERR_PTR(-EINVAL);
164 * Get the ldisc ops - we may need to request them to be loaded
165 * dynamically and try again.
167 ldops = get_ldops(disc);
169 request_module("tty-ldisc-%d", disc);
170 ldops = get_ldops(disc);
172 return ERR_CAST(ldops);
175 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
178 return ERR_PTR(-ENOMEM);
188 * tty_ldisc_put - release the ldisc
190 * Complement of tty_ldisc_get().
192 static inline void tty_ldisc_put(struct tty_ldisc *ld)
194 if (WARN_ON_ONCE(!ld))
201 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
203 return (*pos < NR_LDISCS) ? pos : NULL;
206 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
209 return (*pos < NR_LDISCS) ? pos : NULL;
212 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
216 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
218 int i = *(loff_t *)v;
219 struct tty_ldisc_ops *ldops;
221 ldops = get_ldops(i);
224 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
229 static const struct seq_operations tty_ldiscs_seq_ops = {
230 .start = tty_ldiscs_seq_start,
231 .next = tty_ldiscs_seq_next,
232 .stop = tty_ldiscs_seq_stop,
233 .show = tty_ldiscs_seq_show,
236 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
238 return seq_open(file, &tty_ldiscs_seq_ops);
241 const struct file_operations tty_ldiscs_proc_fops = {
242 .owner = THIS_MODULE,
243 .open = proc_tty_ldiscs_open,
246 .release = seq_release,
250 * tty_ldisc_ref_wait - wait for the tty ldisc
253 * Dereference the line discipline for the terminal and take a
254 * reference to it. If the line discipline is in flux then
255 * wait patiently until it changes.
257 * Note: Must not be called from an IRQ/timer context. The caller
258 * must also be careful not to hold other locks that will deadlock
259 * against a discipline change, such as an existing ldisc reference
260 * (which we check for)
262 * Note: only callable from a file_operations routine (which
263 * guarantees tty->ldisc != NULL when the lock is acquired).
266 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
268 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
269 WARN_ON(!tty->ldisc);
272 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
275 * tty_ldisc_ref - get the tty ldisc
278 * Dereference the line discipline for the terminal and take a
279 * reference to it. If the line discipline is in flux then
280 * return NULL. Can be called from IRQ and timer functions.
283 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
285 struct tty_ldisc *ld = NULL;
287 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
290 ldsem_up_read(&tty->ldisc_sem);
294 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
297 * tty_ldisc_deref - free a tty ldisc reference
298 * @ld: reference to free up
300 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
301 * be called in IRQ context.
304 void tty_ldisc_deref(struct tty_ldisc *ld)
306 ldsem_up_read(&ld->tty->ldisc_sem);
308 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
311 static inline int __lockfunc
312 tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
314 return ldsem_down_write(&tty->ldisc_sem, timeout);
317 static inline int __lockfunc
318 tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
320 return ldsem_down_write_nested(&tty->ldisc_sem,
321 LDISC_SEM_OTHER, timeout);
324 static inline void tty_ldisc_unlock(struct tty_struct *tty)
326 return ldsem_up_write(&tty->ldisc_sem);
329 static int __lockfunc
330 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
331 unsigned long timeout)
336 ret = tty_ldisc_lock(tty, timeout);
338 ret = tty_ldisc_lock_nested(tty2, timeout);
340 tty_ldisc_unlock(tty);
343 /* if this is possible, it has lots of implications */
344 WARN_ON_ONCE(tty == tty2);
345 if (tty2 && tty != tty2) {
346 ret = tty_ldisc_lock(tty2, timeout);
348 ret = tty_ldisc_lock_nested(tty, timeout);
350 tty_ldisc_unlock(tty2);
353 ret = tty_ldisc_lock(tty, timeout);
359 set_bit(TTY_LDISC_HALTED, &tty->flags);
361 set_bit(TTY_LDISC_HALTED, &tty2->flags);
365 static void __lockfunc
366 tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
368 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
371 static void __lockfunc tty_ldisc_unlock_pair(struct tty_struct *tty,
372 struct tty_struct *tty2)
374 tty_ldisc_unlock(tty);
376 tty_ldisc_unlock(tty2);
379 static void __lockfunc tty_ldisc_enable_pair(struct tty_struct *tty,
380 struct tty_struct *tty2)
382 clear_bit(TTY_LDISC_HALTED, &tty->flags);
384 clear_bit(TTY_LDISC_HALTED, &tty2->flags);
386 tty_ldisc_unlock_pair(tty, tty2);
390 * tty_ldisc_flush - flush line discipline queue
393 * Flush the line discipline queue (if any) for this tty. If there
394 * is no line discipline active this is a no-op.
397 void tty_ldisc_flush(struct tty_struct *tty)
399 struct tty_ldisc *ld = tty_ldisc_ref(tty);
401 if (ld->ops->flush_buffer)
402 ld->ops->flush_buffer(tty);
405 tty_buffer_flush(tty);
407 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
410 * tty_set_termios_ldisc - set ldisc field
411 * @tty: tty structure
412 * @num: line discipline number
414 * This is probably overkill for real world processors but
415 * they are not on hot paths so a little discipline won't do
418 * Locking: takes termios_mutex
421 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
423 mutex_lock(&tty->termios_mutex);
424 tty->termios.c_line = num;
425 mutex_unlock(&tty->termios_mutex);
429 * tty_ldisc_open - open a line discipline
430 * @tty: tty we are opening the ldisc on
431 * @ld: discipline to open
433 * A helper opening method. Also a convenient debugging and check
436 * Locking: always called with BTM already held.
439 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
441 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
444 /* BTM here locks versus a hangup event */
445 ret = ld->ops->open(tty);
447 clear_bit(TTY_LDISC_OPEN, &tty->flags);
454 * tty_ldisc_close - close a line discipline
455 * @tty: tty we are opening the ldisc on
456 * @ld: discipline to close
458 * A helper close method. Also a convenient debugging and check
462 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
464 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
465 clear_bit(TTY_LDISC_OPEN, &tty->flags);
471 * tty_ldisc_restore - helper for tty ldisc change
472 * @tty: tty to recover
473 * @old: previous ldisc
475 * Restore the previous line discipline or N_TTY when a line discipline
476 * change fails due to an open error
479 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
482 struct tty_ldisc *new_ldisc;
485 /* There is an outstanding reference here so this is safe */
486 old = tty_ldisc_get(tty, old->ops->num);
487 WARN_ON(IS_ERR(old));
489 tty_set_termios_ldisc(tty, old->ops->num);
490 if (tty_ldisc_open(tty, old) < 0) {
492 /* This driver is always present */
493 new_ldisc = tty_ldisc_get(tty, N_TTY);
494 if (IS_ERR(new_ldisc))
496 tty->ldisc = new_ldisc;
497 tty_set_termios_ldisc(tty, N_TTY);
498 r = tty_ldisc_open(tty, new_ldisc);
500 panic("Couldn't open N_TTY ldisc for "
502 tty_name(tty, buf), r);
507 * tty_set_ldisc - set line discipline
508 * @tty: the terminal to set
509 * @ldisc: the line discipline
511 * Set the discipline of a tty line. Must be called from a process
512 * context. The ldisc change logic has to protect itself against any
513 * overlapping ldisc change (including on the other end of pty pairs),
514 * the close of one side of a tty/pty pair, and eventually hangup.
517 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
520 struct tty_ldisc *o_ldisc, *new_ldisc;
521 struct tty_struct *o_tty = tty->link;
523 new_ldisc = tty_ldisc_get(tty, ldisc);
524 if (IS_ERR(new_ldisc))
525 return PTR_ERR(new_ldisc);
527 retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
529 tty_ldisc_put(new_ldisc);
534 * Check the no-op case
537 if (tty->ldisc->ops->num == ldisc) {
538 tty_ldisc_enable_pair(tty, o_tty);
539 tty_ldisc_put(new_ldisc);
543 /* FIXME: why 'shutoff' input if the ldisc is locked? */
544 tty->receive_room = 0;
546 o_ldisc = tty->ldisc;
549 /* FIXME: for testing only */
550 WARN_ON(test_bit(TTY_HUPPED, &tty->flags));
552 if (test_bit(TTY_HUPPING, &tty->flags)) {
553 /* We were raced by the hangup method. It will have stomped
554 the ldisc data and closed the ldisc down */
555 tty_ldisc_enable_pair(tty, o_tty);
556 tty_ldisc_put(new_ldisc);
561 /* Shutdown the current discipline. */
562 tty_ldisc_close(tty, o_ldisc);
564 /* Now set up the new line discipline. */
565 tty->ldisc = new_ldisc;
566 tty_set_termios_ldisc(tty, ldisc);
568 retval = tty_ldisc_open(tty, new_ldisc);
570 /* Back to the old one or N_TTY if we can't */
571 tty_ldisc_put(new_ldisc);
572 tty_ldisc_restore(tty, o_ldisc);
575 /* At this point we hold a reference to the new ldisc and a
576 a reference to the old ldisc. If we ended up flipping back
577 to the existing ldisc we have two references to it */
579 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
580 tty->ops->set_ldisc(tty);
582 tty_ldisc_put(o_ldisc);
585 * Allow ldisc referencing to occur again
587 tty_ldisc_enable_pair(tty, o_tty);
589 /* Restart the work queue in case no characters kick it off. Safe if
591 schedule_work(&tty->port->buf.work);
593 schedule_work(&o_tty->port->buf.work);
600 * tty_reset_termios - reset terminal state
603 * Restore a terminal to the driver default state.
606 static void tty_reset_termios(struct tty_struct *tty)
608 mutex_lock(&tty->termios_mutex);
609 tty->termios = tty->driver->init_termios;
610 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
611 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
612 mutex_unlock(&tty->termios_mutex);
617 * tty_ldisc_reinit - reinitialise the tty ldisc
618 * @tty: tty to reinit
619 * @ldisc: line discipline to reinitialize
621 * Switch the tty to a line discipline and leave the ldisc
625 static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
627 struct tty_ldisc *ld = tty_ldisc_get(tty, ldisc);
632 tty_ldisc_close(tty, tty->ldisc);
633 tty_ldisc_put(tty->ldisc);
635 * Switch the line discipline back
638 tty_set_termios_ldisc(tty, ldisc);
644 * tty_ldisc_hangup - hangup ldisc reset
645 * @tty: tty being hung up
647 * Some tty devices reset their termios when they receive a hangup
648 * event. In that situation we must also switch back to N_TTY properly
649 * before we reset the termios data.
651 * Locking: We can take the ldisc mutex as the rest of the code is
652 * careful to allow for this.
654 * In the pty pair case this occurs in the close() path of the
655 * tty itself so we must be careful about locking rules.
658 void tty_ldisc_hangup(struct tty_struct *tty)
660 struct tty_ldisc *ld;
661 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
664 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
666 ld = tty_ldisc_ref(tty);
668 if (ld->ops->flush_buffer)
669 ld->ops->flush_buffer(tty);
670 tty_driver_flush_buffer(tty);
671 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
672 ld->ops->write_wakeup)
673 ld->ops->write_wakeup(tty);
675 ld->ops->hangup(tty);
679 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
680 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
685 * Shutdown the current line discipline, and reset it to
688 * Avoid racing set_ldisc or tty_ldisc_release
690 tty_ldisc_lock_pair(tty, tty->link);
695 /* At this point we have a halted ldisc; we want to close it and
696 reopen a new ldisc. We could defer the reopen to the next
697 open but it means auditing a lot of other paths so this is
701 if (!tty_ldisc_reinit(tty, tty->termios.c_line))
702 err = tty_ldisc_open(tty, tty->ldisc);
706 /* If the re-open fails or we reset then go to N_TTY. The
707 N_TTY open cannot fail */
709 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
710 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
713 tty_ldisc_enable_pair(tty, tty->link);
715 tty_reset_termios(tty);
717 tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc);
721 * tty_ldisc_setup - open line discipline
722 * @tty: tty being shut down
723 * @o_tty: pair tty for pty/tty pairs
725 * Called during the initial open of a tty/pty pair in order to set up the
726 * line disciplines and bind them to the tty. This has no locking issues
727 * as the device isn't yet active.
730 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
732 struct tty_ldisc *ld = tty->ldisc;
735 retval = tty_ldisc_open(tty, ld);
740 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
742 tty_ldisc_close(tty, ld);
749 static void tty_ldisc_kill(struct tty_struct *tty)
752 * Now kill off the ldisc
754 tty_ldisc_close(tty, tty->ldisc);
755 tty_ldisc_put(tty->ldisc);
756 /* Force an oops if we mess this up */
759 /* Ensure the next open requests the N_TTY ldisc */
760 tty_set_termios_ldisc(tty, N_TTY);
764 * tty_ldisc_release - release line discipline
765 * @tty: tty being shut down
766 * @o_tty: pair tty for pty/tty pairs
768 * Called during the final close of a tty/pty pair in order to shut down
769 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
770 * ldisc has not been opened.
773 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
776 * Shutdown this line discipline. As this is the final close,
777 * it does not race with the set_ldisc code path.
780 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
782 tty_ldisc_lock_pair(tty, o_tty);
783 tty_lock_pair(tty, o_tty);
787 tty_ldisc_kill(o_tty);
789 tty_unlock_pair(tty, o_tty);
790 tty_ldisc_unlock_pair(tty, o_tty);
792 /* And the memory resources remaining (buffers, termios) will be
793 disposed of when the kref hits zero */
795 tty_ldisc_debug(tty, "ldisc closed\n");
799 * tty_ldisc_init - ldisc setup for new tty
800 * @tty: tty being allocated
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.
806 void tty_ldisc_init(struct tty_struct *tty)
808 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
810 panic("n_tty: init_tty");
815 * tty_ldisc_init - ldisc cleanup for new tty
816 * @tty: tty that was allocated recently
818 * The tty structure must not becompletely set up (tty_ldisc_setup) when
821 void tty_ldisc_deinit(struct tty_struct *tty)
823 tty_ldisc_put(tty->ldisc);
827 void tty_ldisc_begin(void)
829 /* Setup the default TTY line discipline. */
830 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);