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...) ({ \
27 printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
30 #define tty_ldisc_debug(tty, f, args...)
33 /* lockdep nested classes for tty->ldisc_sem */
41 * This guards the refcounted line discipline lists. The lock
42 * must be taken with irqs off because there are hangup path
43 * callers who will do ldisc lookups and cannot sleep.
46 static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
47 /* Line disc dispatch table */
48 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
51 * tty_register_ldisc - install a line discipline
53 * @new_ldisc: pointer to the ldisc object
55 * Installs a new line discipline into the kernel. The discipline
56 * is set up as unreferenced and then made available to the kernel
57 * from this point onwards.
60 * takes tty_ldiscs_lock to guard against ldisc races
63 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
68 if (disc < N_TTY || disc >= NR_LDISCS)
71 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
72 tty_ldiscs[disc] = new_ldisc;
73 new_ldisc->num = disc;
74 new_ldisc->refcount = 0;
75 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
79 EXPORT_SYMBOL(tty_register_ldisc);
82 * tty_unregister_ldisc - unload a line discipline
84 * @new_ldisc: pointer to the ldisc object
86 * Remove a line discipline from the kernel providing it is not
90 * takes tty_ldiscs_lock to guard against ldisc races
93 int tty_unregister_ldisc(int disc)
98 if (disc < N_TTY || disc >= NR_LDISCS)
101 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
102 if (tty_ldiscs[disc]->refcount)
105 tty_ldiscs[disc] = NULL;
106 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
110 EXPORT_SYMBOL(tty_unregister_ldisc);
112 static struct tty_ldisc_ops *get_ldops(int disc)
115 struct tty_ldisc_ops *ldops, *ret;
117 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
118 ret = ERR_PTR(-EINVAL);
119 ldops = tty_ldiscs[disc];
121 ret = ERR_PTR(-EAGAIN);
122 if (try_module_get(ldops->owner)) {
127 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
131 static void put_ldops(struct tty_ldisc_ops *ldops)
135 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
137 module_put(ldops->owner);
138 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
142 * tty_ldisc_get - take a reference to an ldisc
143 * @disc: ldisc number
145 * Takes a reference to a line discipline. Deals with refcounts and
146 * module locking counts. Returns NULL if the discipline is not available.
147 * Returns a pointer to the discipline and bumps the ref count if it is
151 * takes tty_ldiscs_lock to guard against ldisc races
154 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
156 struct tty_ldisc *ld;
157 struct tty_ldisc_ops *ldops;
159 if (disc < N_TTY || disc >= NR_LDISCS)
160 return ERR_PTR(-EINVAL);
163 * Get the ldisc ops - we may need to request them to be loaded
164 * dynamically and try again.
166 ldops = get_ldops(disc);
168 request_module("tty-ldisc-%d", disc);
169 ldops = get_ldops(disc);
171 return ERR_CAST(ldops);
174 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
177 return ERR_PTR(-ENOMEM);
187 * tty_ldisc_put - release the ldisc
189 * Complement of tty_ldisc_get().
191 static inline void tty_ldisc_put(struct tty_ldisc *ld)
193 if (WARN_ON_ONCE(!ld))
200 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
202 return (*pos < NR_LDISCS) ? pos : NULL;
205 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
208 return (*pos < NR_LDISCS) ? pos : NULL;
211 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
215 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
217 int i = *(loff_t *)v;
218 struct tty_ldisc_ops *ldops;
220 ldops = get_ldops(i);
223 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
228 static const struct seq_operations tty_ldiscs_seq_ops = {
229 .start = tty_ldiscs_seq_start,
230 .next = tty_ldiscs_seq_next,
231 .stop = tty_ldiscs_seq_stop,
232 .show = tty_ldiscs_seq_show,
235 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
237 return seq_open(file, &tty_ldiscs_seq_ops);
240 const struct file_operations tty_ldiscs_proc_fops = {
241 .owner = THIS_MODULE,
242 .open = proc_tty_ldiscs_open,
245 .release = seq_release,
249 * tty_ldisc_ref_wait - wait for the tty ldisc
252 * Dereference the line discipline for the terminal and take a
253 * reference to it. If the line discipline is in flux then
254 * wait patiently until it changes.
256 * Note: Must not be called from an IRQ/timer context. The caller
257 * must also be careful not to hold other locks that will deadlock
258 * against a discipline change, such as an existing ldisc reference
259 * (which we check for)
261 * Note: only callable from a file_operations routine (which
262 * guarantees tty->ldisc != NULL when the lock is acquired).
265 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
267 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
268 WARN_ON(!tty->ldisc);
271 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
274 * tty_ldisc_ref - get the tty ldisc
277 * Dereference the line discipline for the terminal and take a
278 * reference to it. If the line discipline is in flux then
279 * return NULL. Can be called from IRQ and timer functions.
282 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
284 struct tty_ldisc *ld = NULL;
286 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
289 ldsem_up_read(&tty->ldisc_sem);
293 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
296 * tty_ldisc_deref - free a tty ldisc reference
297 * @ld: reference to free up
299 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
300 * be called in IRQ context.
303 void tty_ldisc_deref(struct tty_ldisc *ld)
305 ldsem_up_read(&ld->tty->ldisc_sem);
307 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
310 static inline int __lockfunc
311 __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
313 return ldsem_down_write(&tty->ldisc_sem, timeout);
316 static inline int __lockfunc
317 __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
319 return ldsem_down_write_nested(&tty->ldisc_sem,
320 LDISC_SEM_OTHER, timeout);
323 static inline void __tty_ldisc_unlock(struct tty_struct *tty)
325 return ldsem_up_write(&tty->ldisc_sem);
328 static int __lockfunc
329 tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
333 ret = __tty_ldisc_lock(tty, timeout);
336 set_bit(TTY_LDISC_HALTED, &tty->flags);
340 static void tty_ldisc_unlock(struct tty_struct *tty)
342 clear_bit(TTY_LDISC_HALTED, &tty->flags);
343 __tty_ldisc_unlock(tty);
346 static int __lockfunc
347 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
348 unsigned long timeout)
353 ret = __tty_ldisc_lock(tty, timeout);
355 ret = __tty_ldisc_lock_nested(tty2, timeout);
357 __tty_ldisc_unlock(tty);
360 /* if this is possible, it has lots of implications */
361 WARN_ON_ONCE(tty == tty2);
362 if (tty2 && tty != tty2) {
363 ret = __tty_ldisc_lock(tty2, timeout);
365 ret = __tty_ldisc_lock_nested(tty, timeout);
367 __tty_ldisc_unlock(tty2);
370 ret = __tty_ldisc_lock(tty, timeout);
376 set_bit(TTY_LDISC_HALTED, &tty->flags);
378 set_bit(TTY_LDISC_HALTED, &tty2->flags);
382 static void __lockfunc
383 tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
385 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
388 static void __lockfunc tty_ldisc_unlock_pair(struct tty_struct *tty,
389 struct tty_struct *tty2)
391 __tty_ldisc_unlock(tty);
393 __tty_ldisc_unlock(tty2);
396 static void __lockfunc tty_ldisc_enable_pair(struct tty_struct *tty,
397 struct tty_struct *tty2)
399 clear_bit(TTY_LDISC_HALTED, &tty->flags);
401 clear_bit(TTY_LDISC_HALTED, &tty2->flags);
403 tty_ldisc_unlock_pair(tty, tty2);
407 * tty_ldisc_flush - flush line discipline queue
410 * Flush the line discipline queue (if any) for this tty. If there
411 * is no line discipline active this is a no-op.
414 void tty_ldisc_flush(struct tty_struct *tty)
416 struct tty_ldisc *ld = tty_ldisc_ref(tty);
418 if (ld->ops->flush_buffer)
419 ld->ops->flush_buffer(tty);
422 tty_buffer_flush(tty);
424 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
427 * tty_set_termios_ldisc - set ldisc field
428 * @tty: tty structure
429 * @num: line discipline number
431 * This is probably overkill for real world processors but
432 * they are not on hot paths so a little discipline won't do
435 * Locking: takes termios_rwsem
438 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
440 down_write(&tty->termios_rwsem);
441 tty->termios.c_line = num;
442 up_write(&tty->termios_rwsem);
446 * tty_ldisc_open - open a line discipline
447 * @tty: tty we are opening the ldisc on
448 * @ld: discipline to open
450 * A helper opening method. Also a convenient debugging and check
453 * Locking: always called with BTM already held.
456 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
458 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
461 /* BTM here locks versus a hangup event */
462 ret = ld->ops->open(tty);
464 clear_bit(TTY_LDISC_OPEN, &tty->flags);
471 * tty_ldisc_close - close a line discipline
472 * @tty: tty we are opening the ldisc on
473 * @ld: discipline to close
475 * A helper close method. Also a convenient debugging and check
479 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
481 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
482 clear_bit(TTY_LDISC_OPEN, &tty->flags);
488 * tty_ldisc_restore - helper for tty ldisc change
489 * @tty: tty to recover
490 * @old: previous ldisc
492 * Restore the previous line discipline or N_TTY when a line discipline
493 * change fails due to an open error
496 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
499 struct tty_ldisc *new_ldisc;
502 /* There is an outstanding reference here so this is safe */
503 old = tty_ldisc_get(tty, old->ops->num);
504 WARN_ON(IS_ERR(old));
506 tty_set_termios_ldisc(tty, old->ops->num);
507 if (tty_ldisc_open(tty, old) < 0) {
509 /* This driver is always present */
510 new_ldisc = tty_ldisc_get(tty, N_TTY);
511 if (IS_ERR(new_ldisc))
513 tty->ldisc = new_ldisc;
514 tty_set_termios_ldisc(tty, N_TTY);
515 r = tty_ldisc_open(tty, new_ldisc);
517 panic("Couldn't open N_TTY ldisc for "
519 tty_name(tty, buf), r);
524 * tty_set_ldisc - set line discipline
525 * @tty: the terminal to set
526 * @ldisc: the line discipline
528 * Set the discipline of a tty line. Must be called from a process
529 * context. The ldisc change logic has to protect itself against any
530 * overlapping ldisc change (including on the other end of pty pairs),
531 * the close of one side of a tty/pty pair, and eventually hangup.
534 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
537 struct tty_ldisc *old_ldisc, *new_ldisc;
538 struct tty_struct *o_tty = tty->link;
540 new_ldisc = tty_ldisc_get(tty, ldisc);
541 if (IS_ERR(new_ldisc))
542 return PTR_ERR(new_ldisc);
545 retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
547 tty_ldisc_put(new_ldisc);
553 * Check the no-op case
556 if (tty->ldisc->ops->num == ldisc) {
557 tty_ldisc_enable_pair(tty, o_tty);
558 tty_ldisc_put(new_ldisc);
563 old_ldisc = tty->ldisc;
565 if (test_bit(TTY_HUPPED, &tty->flags)) {
566 /* We were raced by the hangup method. It will have stomped
567 the ldisc data and closed the ldisc down */
568 tty_ldisc_enable_pair(tty, o_tty);
569 tty_ldisc_put(new_ldisc);
574 /* Shutdown the old discipline. */
575 tty_ldisc_close(tty, old_ldisc);
577 /* Now set up the new line discipline. */
578 tty->ldisc = new_ldisc;
579 tty_set_termios_ldisc(tty, ldisc);
581 retval = tty_ldisc_open(tty, new_ldisc);
583 /* Back to the old one or N_TTY if we can't */
584 tty_ldisc_put(new_ldisc);
585 tty_ldisc_restore(tty, old_ldisc);
588 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc)
589 tty->ops->set_ldisc(tty);
591 /* At this point we hold a reference to the new ldisc and a
592 reference to the old ldisc, or we hold two references to
593 the old ldisc (if it was restored as part of error cleanup
594 above). In either case, releasing a single reference from
595 the old ldisc is correct. */
597 tty_ldisc_put(old_ldisc);
600 * Allow ldisc referencing to occur again
602 tty_ldisc_enable_pair(tty, o_tty);
604 /* Restart the work queue in case no characters kick it off. Safe if
606 schedule_work(&tty->port->buf.work);
608 schedule_work(&o_tty->port->buf.work);
615 * tty_reset_termios - reset terminal state
618 * Restore a terminal to the driver default state.
621 static void tty_reset_termios(struct tty_struct *tty)
623 down_write(&tty->termios_rwsem);
624 tty->termios = tty->driver->init_termios;
625 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
626 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
627 up_write(&tty->termios_rwsem);
632 * tty_ldisc_reinit - reinitialise the tty ldisc
633 * @tty: tty to reinit
634 * @ldisc: line discipline to reinitialize
636 * Switch the tty to a line discipline and leave the ldisc
640 static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
642 struct tty_ldisc *ld = tty_ldisc_get(tty, ldisc);
647 tty_ldisc_close(tty, tty->ldisc);
648 tty_ldisc_put(tty->ldisc);
650 * Switch the line discipline back
653 tty_set_termios_ldisc(tty, ldisc);
659 * tty_ldisc_hangup - hangup ldisc reset
660 * @tty: tty being hung up
662 * Some tty devices reset their termios when they receive a hangup
663 * event. In that situation we must also switch back to N_TTY properly
664 * before we reset the termios data.
666 * Locking: We can take the ldisc mutex as the rest of the code is
667 * careful to allow for this.
669 * In the pty pair case this occurs in the close() path of the
670 * tty itself so we must be careful about locking rules.
673 void tty_ldisc_hangup(struct tty_struct *tty)
675 struct tty_ldisc *ld;
676 int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
679 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
681 ld = tty_ldisc_ref(tty);
683 if (ld->ops->flush_buffer)
684 ld->ops->flush_buffer(tty);
685 tty_driver_flush_buffer(tty);
686 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
687 ld->ops->write_wakeup)
688 ld->ops->write_wakeup(tty);
690 ld->ops->hangup(tty);
694 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
695 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
698 * Shutdown the current line discipline, and reset it to
701 * Avoid racing set_ldisc or tty_ldisc_release
703 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
707 /* At this point we have a halted ldisc; we want to close it and
708 reopen a new ldisc. We could defer the reopen to the next
709 open but it means auditing a lot of other paths so this is
713 if (!tty_ldisc_reinit(tty, tty->termios.c_line))
714 err = tty_ldisc_open(tty, tty->ldisc);
718 /* If the re-open fails or we reset then go to N_TTY. The
719 N_TTY open cannot fail */
721 BUG_ON(tty_ldisc_reinit(tty, N_TTY));
722 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
725 tty_ldisc_unlock(tty);
727 tty_reset_termios(tty);
729 tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc);
733 * tty_ldisc_setup - open line discipline
734 * @tty: tty being shut down
735 * @o_tty: pair tty for pty/tty pairs
737 * Called during the initial open of a tty/pty pair in order to set up the
738 * line disciplines and bind them to the tty. This has no locking issues
739 * as the device isn't yet active.
742 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
744 struct tty_ldisc *ld = tty->ldisc;
747 retval = tty_ldisc_open(tty, ld);
752 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
754 tty_ldisc_close(tty, ld);
761 static void tty_ldisc_kill(struct tty_struct *tty)
764 * Now kill off the ldisc
766 tty_ldisc_close(tty, tty->ldisc);
767 tty_ldisc_put(tty->ldisc);
768 /* Force an oops if we mess this up */
771 /* Ensure the next open requests the N_TTY ldisc */
772 tty_set_termios_ldisc(tty, N_TTY);
776 * tty_ldisc_release - release line discipline
777 * @tty: tty being shut down (or one end of pty pair)
779 * Called during the final close of a tty or a pty pair in order to shut
780 * down the line discpline layer. On exit, each ldisc assigned is N_TTY and
781 * each ldisc has not been opened.
784 void tty_ldisc_release(struct tty_struct *tty)
786 struct tty_struct *o_tty = tty->link;
789 * Shutdown this line discipline. As this is the final close,
790 * it does not race with the set_ldisc code path.
793 tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
795 tty_ldisc_lock_pair(tty, o_tty);
798 tty_ldisc_kill(o_tty);
799 tty_ldisc_unlock_pair(tty, o_tty);
801 /* And the memory resources remaining (buffers, termios) will be
802 disposed of when the kref hits zero */
804 tty_ldisc_debug(tty, "ldisc closed\n");
808 * tty_ldisc_init - ldisc setup for new tty
809 * @tty: tty being allocated
811 * Set up the line discipline objects for a newly allocated tty. Note that
812 * the tty structure is not completely set up when this call is made.
815 void tty_ldisc_init(struct tty_struct *tty)
817 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
819 panic("n_tty: init_tty");
824 * tty_ldisc_init - ldisc cleanup for new tty
825 * @tty: tty that was allocated recently
827 * The tty structure must not becompletely set up (tty_ldisc_setup) when
830 void tty_ldisc_deinit(struct tty_struct *tty)
832 tty_ldisc_put(tty->ldisc);
836 void tty_ldisc_begin(void)
838 /* Setup the default TTY line discipline. */
839 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);