1 #include <linux/types.h>
2 #include <linux/major.h>
3 #include <linux/errno.h>
4 #include <linux/signal.h>
5 #include <linux/fcntl.h>
6 #include <linux/sched.h>
7 #include <linux/interrupt.h>
9 #include <linux/tty_driver.h>
10 #include <linux/tty_flip.h>
11 #include <linux/devpts_fs.h>
12 #include <linux/file.h>
13 #include <linux/console.h>
14 #include <linux/timer.h>
15 #include <linux/ctype.h>
18 #include <linux/string.h>
19 #include <linux/slab.h>
20 #include <linux/poll.h>
21 #include <linux/proc_fs.h>
22 #include <linux/init.h>
23 #include <linux/module.h>
24 #include <linux/smp_lock.h>
25 #include <linux/device.h>
26 #include <linux/wait.h>
27 #include <linux/bitops.h>
28 #include <linux/delay.h>
29 #include <linux/seq_file.h>
31 #include <linux/uaccess.h>
32 #include <asm/system.h>
34 #include <linux/kbd_kern.h>
35 #include <linux/vt_kern.h>
36 #include <linux/selection.h>
38 #include <linux/kmod.h>
39 #include <linux/nsproxy.h>
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_SPINLOCK(tty_ldisc_lock);
48 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
49 /* Line disc dispatch table */
50 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
53 * tty_register_ldisc - install a line discipline
55 * @new_ldisc: pointer to the ldisc object
57 * Installs a new line discipline into the kernel. The discipline
58 * is set up as unreferenced and then made available to the kernel
59 * from this point onwards.
62 * takes tty_ldisc_lock to guard against ldisc races
65 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
70 if (disc < N_TTY || disc >= NR_LDISCS)
73 spin_lock_irqsave(&tty_ldisc_lock, flags);
74 tty_ldiscs[disc] = new_ldisc;
75 new_ldisc->num = disc;
76 new_ldisc->refcount = 0;
77 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
81 EXPORT_SYMBOL(tty_register_ldisc);
84 * tty_unregister_ldisc - unload a line discipline
86 * @new_ldisc: pointer to the ldisc object
88 * Remove a line discipline from the kernel providing it is not
92 * takes tty_ldisc_lock to guard against ldisc races
95 int tty_unregister_ldisc(int disc)
100 if (disc < N_TTY || disc >= NR_LDISCS)
103 spin_lock_irqsave(&tty_ldisc_lock, flags);
104 if (tty_ldiscs[disc]->refcount)
107 tty_ldiscs[disc] = NULL;
108 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
112 EXPORT_SYMBOL(tty_unregister_ldisc);
116 * tty_ldisc_try_get - try and reference an ldisc
117 * @disc: ldisc number
119 * Attempt to open and lock a line discipline into place. Return
120 * the line discipline refcounted or an error.
123 static struct tty_ldisc *tty_ldisc_try_get(int disc)
126 struct tty_ldisc *ld;
127 struct tty_ldisc_ops *ldops;
130 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
132 return ERR_PTR(-ENOMEM);
134 spin_lock_irqsave(&tty_ldisc_lock, flags);
136 ldops = tty_ldiscs[disc];
137 /* Check the entry is defined */
139 /* If the module is being unloaded we can't use it */
140 if (!try_module_get(ldops->owner))
150 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
159 * tty_ldisc_get - take a reference to an ldisc
160 * @disc: ldisc number
162 * Takes a reference to a line discipline. Deals with refcounts and
163 * module locking counts. Returns NULL if the discipline is not available.
164 * Returns a pointer to the discipline and bumps the ref count if it is
168 * takes tty_ldisc_lock to guard against ldisc races
171 static struct tty_ldisc *tty_ldisc_get(int disc)
173 struct tty_ldisc *ld;
175 if (disc < N_TTY || disc >= NR_LDISCS)
176 return ERR_PTR(-EINVAL);
177 ld = tty_ldisc_try_get(disc);
179 request_module("tty-ldisc-%d", disc);
180 ld = tty_ldisc_try_get(disc);
186 * tty_ldisc_put - drop ldisc reference
189 * Drop a reference to a line discipline. Manage refcounts and
190 * module usage counts. Free the ldisc once the recount hits zero.
193 * takes tty_ldisc_lock to guard against ldisc races
196 static void tty_ldisc_put(struct tty_ldisc *ld)
199 int disc = ld->ops->num;
200 struct tty_ldisc_ops *ldo;
202 BUG_ON(disc < N_TTY || disc >= NR_LDISCS);
204 spin_lock_irqsave(&tty_ldisc_lock, flags);
205 ldo = tty_ldiscs[disc];
206 BUG_ON(ldo->refcount == 0);
208 module_put(ldo->owner);
209 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
213 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
215 return (*pos < NR_LDISCS) ? pos : NULL;
218 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
221 return (*pos < NR_LDISCS) ? pos : NULL;
224 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
228 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
230 int i = *(loff_t *)v;
231 struct tty_ldisc *ld;
233 ld = tty_ldisc_try_get(i);
236 seq_printf(m, "%-10s %2d\n", ld->ops->name ? ld->ops->name : "???", i);
241 static const struct seq_operations tty_ldiscs_seq_ops = {
242 .start = tty_ldiscs_seq_start,
243 .next = tty_ldiscs_seq_next,
244 .stop = tty_ldiscs_seq_stop,
245 .show = tty_ldiscs_seq_show,
248 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
250 return seq_open(file, &tty_ldiscs_seq_ops);
253 const struct file_operations tty_ldiscs_proc_fops = {
254 .owner = THIS_MODULE,
255 .open = proc_tty_ldiscs_open,
258 .release = seq_release,
262 * tty_ldisc_assign - set ldisc on a tty
263 * @tty: tty to assign
264 * @ld: line discipline
266 * Install an instance of a line discipline into a tty structure. The
267 * ldisc must have a reference count above zero to ensure it remains.
268 * The tty instance refcount starts at zero.
271 * Caller must hold references
274 static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
280 * tty_ldisc_try - internal helper
283 * Make a single attempt to grab and bump the refcount on
284 * the tty ldisc. Return 0 on failure or 1 on success. This is
285 * used to implement both the waiting and non waiting versions
288 * Locking: takes tty_ldisc_lock
291 static int tty_ldisc_try(struct tty_struct *tty)
294 struct tty_ldisc *ld;
297 spin_lock_irqsave(&tty_ldisc_lock, flags);
299 if (test_bit(TTY_LDISC, &tty->flags)) {
303 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
308 * tty_ldisc_ref_wait - wait for the tty ldisc
311 * Dereference the line discipline for the terminal and take a
312 * reference to it. If the line discipline is in flux then
313 * wait patiently until it changes.
315 * Note: Must not be called from an IRQ/timer context. The caller
316 * must also be careful not to hold other locks that will deadlock
317 * against a discipline change, such as an existing ldisc reference
318 * (which we check for)
320 * Locking: call functions take tty_ldisc_lock
323 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
325 /* wait_event is a macro */
326 wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
327 WARN_ON(tty->ldisc->refcount == 0);
330 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
333 * tty_ldisc_ref - get the tty ldisc
336 * Dereference the line discipline for the terminal and take a
337 * reference to it. If the line discipline is in flux then
338 * return NULL. Can be called from IRQ and timer functions.
340 * Locking: called functions take tty_ldisc_lock
343 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
345 if (tty_ldisc_try(tty))
349 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
352 * tty_ldisc_deref - free a tty ldisc reference
353 * @ld: reference to free up
355 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
356 * be called in IRQ context.
358 * Locking: takes tty_ldisc_lock
361 void tty_ldisc_deref(struct tty_ldisc *ld)
367 spin_lock_irqsave(&tty_ldisc_lock, flags);
368 if (ld->refcount == 0)
369 printk(KERN_ERR "tty_ldisc_deref: no references.\n");
372 if (ld->refcount == 0)
373 wake_up(&tty_ldisc_wait);
374 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
376 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
379 * tty_ldisc_enable - allow ldisc use
380 * @tty: terminal to activate ldisc on
382 * Set the TTY_LDISC flag when the line discipline can be called
383 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
384 * changing flag to indicate any ldisc change is now over.
386 * Note: nobody should set the TTY_LDISC bit except via this function.
387 * Clearing directly is allowed.
390 void tty_ldisc_enable(struct tty_struct *tty)
392 set_bit(TTY_LDISC, &tty->flags);
393 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
394 wake_up(&tty_ldisc_wait);
398 * tty_ldisc_flush - flush line discipline queue
401 * Flush the line discipline queue (if any) for this tty. If there
402 * is no line discipline active this is a no-op.
405 void tty_ldisc_flush(struct tty_struct *tty)
407 struct tty_ldisc *ld = tty_ldisc_ref(tty);
409 if (ld->ops->flush_buffer)
410 ld->ops->flush_buffer(tty);
413 tty_buffer_flush(tty);
415 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
418 * tty_set_termios_ldisc - set ldisc field
419 * @tty: tty structure
420 * @num: line discipline number
422 * This is probably overkill for real world processors but
423 * they are not on hot paths so a little discipline won't do
426 * Locking: takes termios_mutex
429 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
431 mutex_lock(&tty->termios_mutex);
432 tty->termios->c_line = num;
433 mutex_unlock(&tty->termios_mutex);
437 * tty_ldisc_open - open a line discipline
438 * @tty: tty we are opening the ldisc on
439 * @ld: discipline to open
441 * A helper opening method. Also a convenient debugging and check
445 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
447 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
449 return ld->ops->open(tty);
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(old->ops->num);
487 WARN_ON(IS_ERR(old));
488 tty_ldisc_assign(tty, 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(N_TTY);
494 if (IS_ERR(new_ldisc))
496 tty_ldisc_assign(tty, 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_ldisc_halt - shut down the line discipline
510 * Shut down the line discipline and work queue for this tty device.
511 * The TTY_LDISC flag being cleared ensures no further references can
512 * be obtained while the delayed work queue halt ensures that no more
513 * data is fed to the ldisc.
515 * In order to wait for any existing references to complete see
516 * tty_ldisc_wait_idle.
519 static int tty_ldisc_halt(struct tty_struct *tty)
521 clear_bit(TTY_LDISC, &tty->flags);
522 return cancel_delayed_work(&tty->buf.work);
526 * tty_ldisc_wait_idle - wait for the ldisc to become idle
527 * @tty: tty to wait for
529 * Wait for the line discipline to become idle. The discipline must
530 * have been halted for this to guarantee it remains idle.
532 * tty_ldisc_lock protects the ref counts currently.
535 static int tty_ldisc_wait_idle(struct tty_struct *tty)
538 spin_lock_irqsave(&tty_ldisc_lock, flags);
539 while (tty->ldisc->refcount) {
540 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
541 if (wait_event_timeout(tty_ldisc_wait,
542 tty->ldisc->refcount == 0, 5 * HZ) == 0)
544 spin_lock_irqsave(&tty_ldisc_lock, flags);
546 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
551 * tty_set_ldisc - set line discipline
552 * @tty: the terminal to set
553 * @ldisc: the line discipline
555 * Set the discipline of a tty line. Must be called from a process
556 * context. The ldisc change logic has to protect itself against any
557 * overlapping ldisc change (including on the other end of pty pairs),
558 * the close of one side of a tty/pty pair, and eventually hangup.
560 * Locking: takes tty_ldisc_lock, termios_mutex
563 int tty_set_ldisc(struct tty_struct *tty, int ldisc)
566 struct tty_ldisc *o_ldisc, *new_ldisc;
567 int work, o_work = 0;
568 struct tty_struct *o_tty;
570 new_ldisc = tty_ldisc_get(ldisc);
571 if (IS_ERR(new_ldisc))
572 return PTR_ERR(new_ldisc);
575 * We need to look at the tty locking here for pty/tty pairs
576 * when both sides try to change in parallel.
579 o_tty = tty->link; /* o_tty is the pty side or NULL */
583 * Check the no-op case
586 if (tty->ldisc->ops->num == ldisc) {
587 tty_ldisc_put(new_ldisc);
592 * Problem: What do we do if this blocks ?
593 * We could deadlock here
596 tty_wait_until_sent(tty, 0);
598 mutex_lock(&tty->ldisc_mutex);
601 * We could be midstream of another ldisc change which has
602 * dropped the lock during processing. If so we need to wait.
605 while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
606 mutex_unlock(&tty->ldisc_mutex);
607 wait_event(tty_ldisc_wait,
608 test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
609 mutex_lock(&tty->ldisc_mutex);
611 set_bit(TTY_LDISC_CHANGING, &tty->flags);
614 * No more input please, we are switching. The new ldisc
615 * will update this value in the ldisc open function
618 tty->receive_room = 0;
620 o_ldisc = tty->ldisc;
622 * Make sure we don't change while someone holds a
623 * reference to the line discipline. The TTY_LDISC bit
624 * prevents anyone taking a reference once it is clear.
625 * We need the lock to avoid racing reference takers.
627 * We must clear the TTY_LDISC bit here to avoid a livelock
628 * with a userspace app continually trying to use the tty in
629 * parallel to the change and re-referencing the tty.
632 work = tty_ldisc_halt(tty);
634 o_work = tty_ldisc_halt(o_tty);
637 * Wait for ->hangup_work and ->buf.work handlers to terminate.
638 * We must drop the mutex here in case a hangup is also in process.
641 mutex_unlock(&tty->ldisc_mutex);
643 flush_scheduled_work();
645 /* Let any existing reference holders finish */
646 retval = tty_ldisc_wait_idle(tty);
648 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
649 tty_ldisc_put(new_ldisc);
653 mutex_lock(&tty->ldisc_mutex);
654 if (test_bit(TTY_HUPPED, &tty->flags)) {
655 /* We were raced by the hangup method. It will have stomped
656 the ldisc data and closed the ldisc down */
657 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
658 mutex_unlock(&tty->ldisc_mutex);
659 tty_ldisc_put(new_ldisc);
663 /* Shutdown the current discipline. */
664 tty_ldisc_close(tty, o_ldisc);
666 /* Now set up the new line discipline. */
667 tty_ldisc_assign(tty, new_ldisc);
668 tty_set_termios_ldisc(tty, ldisc);
670 retval = tty_ldisc_open(tty, new_ldisc);
672 /* Back to the old one or N_TTY if we can't */
673 tty_ldisc_put(new_ldisc);
674 tty_ldisc_restore(tty, o_ldisc);
677 /* At this point we hold a reference to the new ldisc and a
678 a reference to the old ldisc. If we ended up flipping back
679 to the existing ldisc we have two references to it */
681 if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
682 tty->ops->set_ldisc(tty);
684 tty_ldisc_put(o_ldisc);
687 * Allow ldisc referencing to occur again
690 tty_ldisc_enable(tty);
692 tty_ldisc_enable(o_tty);
694 /* Restart the work queue in case no characters kick it off. Safe if
697 schedule_delayed_work(&tty->buf.work, 1);
699 schedule_delayed_work(&o_tty->buf.work, 1);
700 mutex_unlock(&tty->ldisc_mutex);
705 * tty_reset_termios - reset terminal state
708 * Restore a terminal to the driver default state.
711 static void tty_reset_termios(struct tty_struct *tty)
713 mutex_lock(&tty->termios_mutex);
714 *tty->termios = tty->driver->init_termios;
715 tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
716 tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
717 mutex_unlock(&tty->termios_mutex);
722 * tty_ldisc_reinit - reinitialise the tty ldisc
723 * @tty: tty to reinit
725 * Switch the tty back to N_TTY line discipline and leave the
729 static void tty_ldisc_reinit(struct tty_struct *tty)
731 struct tty_ldisc *ld;
733 tty_ldisc_close(tty, tty->ldisc);
734 tty_ldisc_put(tty->ldisc);
737 * Switch the line discipline back
739 ld = tty_ldisc_get(N_TTY);
741 tty_ldisc_assign(tty, ld);
742 tty_set_termios_ldisc(tty, N_TTY);
746 * tty_ldisc_hangup - hangup ldisc reset
747 * @tty: tty being hung up
749 * Some tty devices reset their termios when they receive a hangup
750 * event. In that situation we must also switch back to N_TTY properly
751 * before we reset the termios data.
753 * Locking: We can take the ldisc mutex as the rest of the code is
754 * careful to allow for this.
756 * In the pty pair case this occurs in the close() path of the
757 * tty itself so we must be careful about locking rules.
760 void tty_ldisc_hangup(struct tty_struct *tty)
762 struct tty_ldisc *ld;
765 * FIXME! What are the locking issues here? This may me overdoing
766 * things... This question is especially important now that we've
767 * removed the irqlock.
769 ld = tty_ldisc_ref(tty);
771 /* We may have no line discipline at this point */
772 if (ld->ops->flush_buffer)
773 ld->ops->flush_buffer(tty);
774 tty_driver_flush_buffer(tty);
775 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
776 ld->ops->write_wakeup)
777 ld->ops->write_wakeup(tty);
779 ld->ops->hangup(tty);
783 * FIXME: Once we trust the LDISC code better we can wait here for
784 * ldisc completion and fix the driver call race
786 wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
787 wake_up_interruptible_poll(&tty->read_wait, POLLIN);
789 * Shutdown the current line discipline, and reset it to
792 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
793 /* Avoid racing set_ldisc */
794 mutex_lock(&tty->ldisc_mutex);
795 /* Switch back to N_TTY */
796 tty_ldisc_reinit(tty);
797 /* At this point we have a closed ldisc and we want to
798 reopen it. We could defer this to the next open but
799 it means auditing a lot of other paths so this is a FIXME */
800 WARN_ON(tty_ldisc_open(tty, tty->ldisc));
801 tty_ldisc_enable(tty);
802 mutex_unlock(&tty->ldisc_mutex);
803 tty_reset_termios(tty);
808 * tty_ldisc_setup - open line discipline
809 * @tty: tty being shut down
810 * @o_tty: pair tty for pty/tty pairs
812 * Called during the initial open of a tty/pty pair in order to set up the
813 * line disciplines and bind them to the tty. This has no locking issues
814 * as the device isn't yet active.
817 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
819 struct tty_ldisc *ld = tty->ldisc;
822 retval = tty_ldisc_open(tty, ld);
827 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
829 tty_ldisc_close(tty, ld);
832 tty_ldisc_enable(o_tty);
834 tty_ldisc_enable(tty);
838 * tty_ldisc_release - release line discipline
839 * @tty: tty being shut down
840 * @o_tty: pair tty for pty/tty pairs
842 * Called during the final close of a tty/pty pair in order to shut down
843 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
844 * ldisc has not been opened.
847 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
850 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
851 * kill any delayed work. As this is the final close it does not
852 * race with the set_ldisc code path.
856 flush_scheduled_work();
859 * Wait for any short term users (we know they are just driver
860 * side waiters as the file is closing so user count on the file
864 tty_ldisc_wait_idle(tty);
867 * Shutdown the current line discipline, and reset it to N_TTY.
869 * FIXME: this MUST get fixed for the new reflocking
872 tty_ldisc_reinit(tty);
873 /* This will need doing differently if we need to lock */
875 tty_ldisc_release(o_tty, NULL);
879 * tty_ldisc_init - ldisc setup for new tty
880 * @tty: tty being allocated
882 * Set up the line discipline objects for a newly allocated tty. Note that
883 * the tty structure is not completely set up when this call is made.
886 void tty_ldisc_init(struct tty_struct *tty)
888 struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
890 panic("n_tty: init_tty");
891 tty_ldisc_assign(tty, ld);
894 void tty_ldisc_begin(void)
896 /* Setup the default TTY line discipline. */
897 (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);