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/device.h>
25 #include <linux/wait.h>
26 #include <linux/bitops.h>
27 #include <linux/delay.h>
28 #include <linux/seq_file.h>
30 #include <linux/uaccess.h>
31 #include <asm/system.h>
33 #include <linux/kbd_kern.h>
34 #include <linux/vt_kern.h>
35 #include <linux/selection.h>
37 #include <linux/kmod.h>
38 #include <linux/nsproxy.h>
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_SPINLOCK(tty_ldisc_lock
);
47 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait
);
48 /* Line disc dispatch table */
49 static struct tty_ldisc_ops
*tty_ldiscs
[NR_LDISCS
];
51 static inline struct tty_ldisc
*get_ldisc(struct tty_ldisc
*ld
)
54 atomic_inc(&ld
->users
);
58 static inline void put_ldisc(struct tty_ldisc
*ld
)
60 if (WARN_ON_ONCE(!ld
))
64 * If this is the last user, free the ldisc, and
65 * release the ldisc ops.
67 if (atomic_dec_and_test(&ld
->users
)) {
69 struct tty_ldisc_ops
*ldo
= ld
->ops
;
72 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
74 module_put(ldo
->owner
);
75 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
80 * tty_register_ldisc - install a line discipline
82 * @new_ldisc: pointer to the ldisc object
84 * Installs a new line discipline into the kernel. The discipline
85 * is set up as unreferenced and then made available to the kernel
86 * from this point onwards.
89 * takes tty_ldisc_lock to guard against ldisc races
92 int tty_register_ldisc(int disc
, struct tty_ldisc_ops
*new_ldisc
)
97 if (disc
< N_TTY
|| disc
>= NR_LDISCS
)
100 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
101 tty_ldiscs
[disc
] = new_ldisc
;
102 new_ldisc
->num
= disc
;
103 new_ldisc
->refcount
= 0;
104 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
108 EXPORT_SYMBOL(tty_register_ldisc
);
111 * tty_unregister_ldisc - unload a line discipline
112 * @disc: ldisc number
113 * @new_ldisc: pointer to the ldisc object
115 * Remove a line discipline from the kernel providing it is not
119 * takes tty_ldisc_lock to guard against ldisc races
122 int tty_unregister_ldisc(int disc
)
127 if (disc
< N_TTY
|| disc
>= NR_LDISCS
)
130 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
131 if (tty_ldiscs
[disc
]->refcount
)
134 tty_ldiscs
[disc
] = NULL
;
135 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
139 EXPORT_SYMBOL(tty_unregister_ldisc
);
143 * tty_ldisc_try_get - try and reference an ldisc
144 * @disc: ldisc number
146 * Attempt to open and lock a line discipline into place. Return
147 * the line discipline refcounted or an error.
150 static struct tty_ldisc
*tty_ldisc_try_get(int disc
)
153 struct tty_ldisc
*ld
;
154 struct tty_ldisc_ops
*ldops
;
157 ld
= kmalloc(sizeof(struct tty_ldisc
), GFP_KERNEL
);
159 return ERR_PTR(-ENOMEM
);
161 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
163 ldops
= tty_ldiscs
[disc
];
164 /* Check the entry is defined */
166 /* If the module is being unloaded we can't use it */
167 if (!try_module_get(ldops
->owner
))
173 atomic_set(&ld
->users
, 1);
177 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
186 * tty_ldisc_get - take a reference to an ldisc
187 * @disc: ldisc number
189 * Takes a reference to a line discipline. Deals with refcounts and
190 * module locking counts. Returns NULL if the discipline is not available.
191 * Returns a pointer to the discipline and bumps the ref count if it is
195 * takes tty_ldisc_lock to guard against ldisc races
198 static struct tty_ldisc
*tty_ldisc_get(int disc
)
200 struct tty_ldisc
*ld
;
202 if (disc
< N_TTY
|| disc
>= NR_LDISCS
)
203 return ERR_PTR(-EINVAL
);
204 ld
= tty_ldisc_try_get(disc
);
206 request_module("tty-ldisc-%d", disc
);
207 ld
= tty_ldisc_try_get(disc
);
212 static void *tty_ldiscs_seq_start(struct seq_file
*m
, loff_t
*pos
)
214 return (*pos
< NR_LDISCS
) ? pos
: NULL
;
217 static void *tty_ldiscs_seq_next(struct seq_file
*m
, void *v
, loff_t
*pos
)
220 return (*pos
< NR_LDISCS
) ? pos
: NULL
;
223 static void tty_ldiscs_seq_stop(struct seq_file
*m
, void *v
)
227 static int tty_ldiscs_seq_show(struct seq_file
*m
, void *v
)
229 int i
= *(loff_t
*)v
;
230 struct tty_ldisc
*ld
;
232 ld
= tty_ldisc_try_get(i
);
235 seq_printf(m
, "%-10s %2d\n", ld
->ops
->name
? ld
->ops
->name
: "???", i
);
240 static const struct seq_operations tty_ldiscs_seq_ops
= {
241 .start
= tty_ldiscs_seq_start
,
242 .next
= tty_ldiscs_seq_next
,
243 .stop
= tty_ldiscs_seq_stop
,
244 .show
= tty_ldiscs_seq_show
,
247 static int proc_tty_ldiscs_open(struct inode
*inode
, struct file
*file
)
249 return seq_open(file
, &tty_ldiscs_seq_ops
);
252 const struct file_operations tty_ldiscs_proc_fops
= {
253 .owner
= THIS_MODULE
,
254 .open
= proc_tty_ldiscs_open
,
257 .release
= seq_release
,
261 * tty_ldisc_assign - set ldisc on a tty
262 * @tty: tty to assign
263 * @ld: line discipline
265 * Install an instance of a line discipline into a tty structure. The
266 * ldisc must have a reference count above zero to ensure it remains.
267 * The tty instance refcount starts at zero.
270 * Caller must hold references
273 static void tty_ldisc_assign(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
279 * tty_ldisc_try - internal helper
282 * Make a single attempt to grab and bump the refcount on
283 * the tty ldisc. Return 0 on failure or 1 on success. This is
284 * used to implement both the waiting and non waiting versions
287 * Locking: takes tty_ldisc_lock
290 static struct tty_ldisc
*tty_ldisc_try(struct tty_struct
*tty
)
293 struct tty_ldisc
*ld
;
295 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
297 if (test_bit(TTY_LDISC
, &tty
->flags
))
298 ld
= get_ldisc(tty
->ldisc
);
299 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
304 * tty_ldisc_ref_wait - wait for the tty ldisc
307 * Dereference the line discipline for the terminal and take a
308 * reference to it. If the line discipline is in flux then
309 * wait patiently until it changes.
311 * Note: Must not be called from an IRQ/timer context. The caller
312 * must also be careful not to hold other locks that will deadlock
313 * against a discipline change, such as an existing ldisc reference
314 * (which we check for)
316 * Locking: call functions take tty_ldisc_lock
319 struct tty_ldisc
*tty_ldisc_ref_wait(struct tty_struct
*tty
)
321 struct tty_ldisc
*ld
;
323 /* wait_event is a macro */
324 wait_event(tty_ldisc_wait
, (ld
= tty_ldisc_try(tty
)) != NULL
);
327 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait
);
330 * tty_ldisc_ref - get the tty ldisc
333 * Dereference the line discipline for the terminal and take a
334 * reference to it. If the line discipline is in flux then
335 * return NULL. Can be called from IRQ and timer functions.
337 * Locking: called functions take tty_ldisc_lock
340 struct tty_ldisc
*tty_ldisc_ref(struct tty_struct
*tty
)
342 return tty_ldisc_try(tty
);
344 EXPORT_SYMBOL_GPL(tty_ldisc_ref
);
347 * tty_ldisc_deref - free a tty ldisc reference
348 * @ld: reference to free up
350 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
351 * be called in IRQ context.
353 * Locking: takes tty_ldisc_lock
356 void tty_ldisc_deref(struct tty_ldisc
*ld
)
360 EXPORT_SYMBOL_GPL(tty_ldisc_deref
);
362 static inline void tty_ldisc_put(struct tty_ldisc
*ld
)
368 * tty_ldisc_enable - allow ldisc use
369 * @tty: terminal to activate ldisc on
371 * Set the TTY_LDISC flag when the line discipline can be called
372 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
373 * changing flag to indicate any ldisc change is now over.
375 * Note: nobody should set the TTY_LDISC bit except via this function.
376 * Clearing directly is allowed.
379 void tty_ldisc_enable(struct tty_struct
*tty
)
381 set_bit(TTY_LDISC
, &tty
->flags
);
382 clear_bit(TTY_LDISC_CHANGING
, &tty
->flags
);
383 wake_up(&tty_ldisc_wait
);
387 * tty_ldisc_flush - flush line discipline queue
390 * Flush the line discipline queue (if any) for this tty. If there
391 * is no line discipline active this is a no-op.
394 void tty_ldisc_flush(struct tty_struct
*tty
)
396 struct tty_ldisc
*ld
= tty_ldisc_ref(tty
);
398 if (ld
->ops
->flush_buffer
)
399 ld
->ops
->flush_buffer(tty
);
402 tty_buffer_flush(tty
);
404 EXPORT_SYMBOL_GPL(tty_ldisc_flush
);
407 * tty_set_termios_ldisc - set ldisc field
408 * @tty: tty structure
409 * @num: line discipline number
411 * This is probably overkill for real world processors but
412 * they are not on hot paths so a little discipline won't do
415 * Locking: takes termios_mutex
418 static void tty_set_termios_ldisc(struct tty_struct
*tty
, int num
)
420 mutex_lock(&tty
->termios_mutex
);
421 tty
->termios
->c_line
= num
;
422 mutex_unlock(&tty
->termios_mutex
);
426 * tty_ldisc_open - open a line discipline
427 * @tty: tty we are opening the ldisc on
428 * @ld: discipline to open
430 * A helper opening method. Also a convenient debugging and check
434 static int tty_ldisc_open(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
436 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN
, &tty
->flags
));
438 return ld
->ops
->open(tty
);
443 * tty_ldisc_close - close a line discipline
444 * @tty: tty we are opening the ldisc on
445 * @ld: discipline to close
447 * A helper close method. Also a convenient debugging and check
451 static void tty_ldisc_close(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
453 WARN_ON(!test_bit(TTY_LDISC_OPEN
, &tty
->flags
));
454 clear_bit(TTY_LDISC_OPEN
, &tty
->flags
);
460 * tty_ldisc_restore - helper for tty ldisc change
461 * @tty: tty to recover
462 * @old: previous ldisc
464 * Restore the previous line discipline or N_TTY when a line discipline
465 * change fails due to an open error
468 static void tty_ldisc_restore(struct tty_struct
*tty
, struct tty_ldisc
*old
)
471 struct tty_ldisc
*new_ldisc
;
474 /* There is an outstanding reference here so this is safe */
475 old
= tty_ldisc_get(old
->ops
->num
);
476 WARN_ON(IS_ERR(old
));
477 tty_ldisc_assign(tty
, old
);
478 tty_set_termios_ldisc(tty
, old
->ops
->num
);
479 if (tty_ldisc_open(tty
, old
) < 0) {
481 /* This driver is always present */
482 new_ldisc
= tty_ldisc_get(N_TTY
);
483 if (IS_ERR(new_ldisc
))
485 tty_ldisc_assign(tty
, new_ldisc
);
486 tty_set_termios_ldisc(tty
, N_TTY
);
487 r
= tty_ldisc_open(tty
, new_ldisc
);
489 panic("Couldn't open N_TTY ldisc for "
491 tty_name(tty
, buf
), r
);
496 * tty_ldisc_halt - shut down the line discipline
499 * Shut down the line discipline and work queue for this tty device.
500 * The TTY_LDISC flag being cleared ensures no further references can
501 * be obtained while the delayed work queue halt ensures that no more
502 * data is fed to the ldisc.
504 * In order to wait for any existing references to complete see
505 * tty_ldisc_wait_idle.
508 static int tty_ldisc_halt(struct tty_struct
*tty
)
510 clear_bit(TTY_LDISC
, &tty
->flags
);
511 return cancel_delayed_work(&tty
->buf
.work
);
515 * tty_set_ldisc - set line discipline
516 * @tty: the terminal to set
517 * @ldisc: the line discipline
519 * Set the discipline of a tty line. Must be called from a process
520 * context. The ldisc change logic has to protect itself against any
521 * overlapping ldisc change (including on the other end of pty pairs),
522 * the close of one side of a tty/pty pair, and eventually hangup.
524 * Locking: takes tty_ldisc_lock, termios_mutex
527 int tty_set_ldisc(struct tty_struct
*tty
, int ldisc
)
530 struct tty_ldisc
*o_ldisc
, *new_ldisc
;
531 int work
, o_work
= 0;
532 struct tty_struct
*o_tty
;
534 new_ldisc
= tty_ldisc_get(ldisc
);
535 if (IS_ERR(new_ldisc
))
536 return PTR_ERR(new_ldisc
);
539 * We need to look at the tty locking here for pty/tty pairs
540 * when both sides try to change in parallel.
543 o_tty
= tty
->link
; /* o_tty is the pty side or NULL */
547 * Check the no-op case
550 if (tty
->ldisc
->ops
->num
== ldisc
) {
551 tty_ldisc_put(new_ldisc
);
556 * Problem: What do we do if this blocks ?
557 * We could deadlock here
560 tty_wait_until_sent(tty
, 0);
562 mutex_lock(&tty
->ldisc_mutex
);
565 * We could be midstream of another ldisc change which has
566 * dropped the lock during processing. If so we need to wait.
569 while (test_bit(TTY_LDISC_CHANGING
, &tty
->flags
)) {
570 mutex_unlock(&tty
->ldisc_mutex
);
571 wait_event(tty_ldisc_wait
,
572 test_bit(TTY_LDISC_CHANGING
, &tty
->flags
) == 0);
573 mutex_lock(&tty
->ldisc_mutex
);
575 set_bit(TTY_LDISC_CHANGING
, &tty
->flags
);
578 * No more input please, we are switching. The new ldisc
579 * will update this value in the ldisc open function
582 tty
->receive_room
= 0;
584 o_ldisc
= tty
->ldisc
;
586 * Make sure we don't change while someone holds a
587 * reference to the line discipline. The TTY_LDISC bit
588 * prevents anyone taking a reference once it is clear.
589 * We need the lock to avoid racing reference takers.
591 * We must clear the TTY_LDISC bit here to avoid a livelock
592 * with a userspace app continually trying to use the tty in
593 * parallel to the change and re-referencing the tty.
596 work
= tty_ldisc_halt(tty
);
598 o_work
= tty_ldisc_halt(o_tty
);
601 * Wait for ->hangup_work and ->buf.work handlers to terminate.
602 * We must drop the mutex here in case a hangup is also in process.
605 mutex_unlock(&tty
->ldisc_mutex
);
607 flush_scheduled_work();
609 mutex_lock(&tty
->ldisc_mutex
);
610 if (test_bit(TTY_HUPPED
, &tty
->flags
)) {
611 /* We were raced by the hangup method. It will have stomped
612 the ldisc data and closed the ldisc down */
613 clear_bit(TTY_LDISC_CHANGING
, &tty
->flags
);
614 mutex_unlock(&tty
->ldisc_mutex
);
615 tty_ldisc_put(new_ldisc
);
619 /* Shutdown the current discipline. */
620 tty_ldisc_close(tty
, o_ldisc
);
622 /* Now set up the new line discipline. */
623 tty_ldisc_assign(tty
, new_ldisc
);
624 tty_set_termios_ldisc(tty
, ldisc
);
626 retval
= tty_ldisc_open(tty
, new_ldisc
);
628 /* Back to the old one or N_TTY if we can't */
629 tty_ldisc_put(new_ldisc
);
630 tty_ldisc_restore(tty
, o_ldisc
);
633 /* At this point we hold a reference to the new ldisc and a
634 a reference to the old ldisc. If we ended up flipping back
635 to the existing ldisc we have two references to it */
637 if (tty
->ldisc
->ops
->num
!= o_ldisc
->ops
->num
&& tty
->ops
->set_ldisc
)
638 tty
->ops
->set_ldisc(tty
);
640 tty_ldisc_put(o_ldisc
);
643 * Allow ldisc referencing to occur again
646 tty_ldisc_enable(tty
);
648 tty_ldisc_enable(o_tty
);
650 /* Restart the work queue in case no characters kick it off. Safe if
653 schedule_delayed_work(&tty
->buf
.work
, 1);
655 schedule_delayed_work(&o_tty
->buf
.work
, 1);
656 mutex_unlock(&tty
->ldisc_mutex
);
661 * tty_reset_termios - reset terminal state
664 * Restore a terminal to the driver default state.
667 static void tty_reset_termios(struct tty_struct
*tty
)
669 mutex_lock(&tty
->termios_mutex
);
670 *tty
->termios
= tty
->driver
->init_termios
;
671 tty
->termios
->c_ispeed
= tty_termios_input_baud_rate(tty
->termios
);
672 tty
->termios
->c_ospeed
= tty_termios_baud_rate(tty
->termios
);
673 mutex_unlock(&tty
->termios_mutex
);
678 * tty_ldisc_reinit - reinitialise the tty ldisc
679 * @tty: tty to reinit
681 * Switch the tty back to N_TTY line discipline and leave the
685 static void tty_ldisc_reinit(struct tty_struct
*tty
)
687 struct tty_ldisc
*ld
;
689 tty_ldisc_close(tty
, tty
->ldisc
);
690 tty_ldisc_put(tty
->ldisc
);
693 * Switch the line discipline back
695 ld
= tty_ldisc_get(N_TTY
);
697 tty_ldisc_assign(tty
, ld
);
698 tty_set_termios_ldisc(tty
, N_TTY
);
702 * tty_ldisc_hangup - hangup ldisc reset
703 * @tty: tty being hung up
705 * Some tty devices reset their termios when they receive a hangup
706 * event. In that situation we must also switch back to N_TTY properly
707 * before we reset the termios data.
709 * Locking: We can take the ldisc mutex as the rest of the code is
710 * careful to allow for this.
712 * In the pty pair case this occurs in the close() path of the
713 * tty itself so we must be careful about locking rules.
716 void tty_ldisc_hangup(struct tty_struct
*tty
)
718 struct tty_ldisc
*ld
;
721 * FIXME! What are the locking issues here? This may me overdoing
722 * things... This question is especially important now that we've
723 * removed the irqlock.
725 ld
= tty_ldisc_ref(tty
);
727 /* We may have no line discipline at this point */
728 if (ld
->ops
->flush_buffer
)
729 ld
->ops
->flush_buffer(tty
);
730 tty_driver_flush_buffer(tty
);
731 if ((test_bit(TTY_DO_WRITE_WAKEUP
, &tty
->flags
)) &&
732 ld
->ops
->write_wakeup
)
733 ld
->ops
->write_wakeup(tty
);
735 ld
->ops
->hangup(tty
);
739 * FIXME: Once we trust the LDISC code better we can wait here for
740 * ldisc completion and fix the driver call race
742 wake_up_interruptible_poll(&tty
->write_wait
, POLLOUT
);
743 wake_up_interruptible_poll(&tty
->read_wait
, POLLIN
);
745 * Shutdown the current line discipline, and reset it to
748 if (tty
->driver
->flags
& TTY_DRIVER_RESET_TERMIOS
) {
749 /* Avoid racing set_ldisc or tty_ldisc_release */
750 mutex_lock(&tty
->ldisc_mutex
);
751 if (tty
->ldisc
) { /* Not yet closed */
752 /* Switch back to N_TTY */
754 tty_ldisc_reinit(tty
);
755 /* At this point we have a closed ldisc and we want to
756 reopen it. We could defer this to the next open but
757 it means auditing a lot of other paths so this is
759 WARN_ON(tty_ldisc_open(tty
, tty
->ldisc
));
760 tty_ldisc_enable(tty
);
762 mutex_unlock(&tty
->ldisc_mutex
);
763 tty_reset_termios(tty
);
768 * tty_ldisc_setup - open line discipline
769 * @tty: tty being shut down
770 * @o_tty: pair tty for pty/tty pairs
772 * Called during the initial open of a tty/pty pair in order to set up the
773 * line disciplines and bind them to the tty. This has no locking issues
774 * as the device isn't yet active.
777 int tty_ldisc_setup(struct tty_struct
*tty
, struct tty_struct
*o_tty
)
779 struct tty_ldisc
*ld
= tty
->ldisc
;
782 retval
= tty_ldisc_open(tty
, ld
);
787 retval
= tty_ldisc_open(o_tty
, o_tty
->ldisc
);
789 tty_ldisc_close(tty
, ld
);
792 tty_ldisc_enable(o_tty
);
794 tty_ldisc_enable(tty
);
798 * tty_ldisc_release - release line discipline
799 * @tty: tty being shut down
800 * @o_tty: pair tty for pty/tty pairs
802 * Called during the final close of a tty/pty pair in order to shut down
803 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
804 * ldisc has not been opened.
807 void tty_ldisc_release(struct tty_struct
*tty
, struct tty_struct
*o_tty
)
810 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
811 * kill any delayed work. As this is the final close it does not
812 * race with the set_ldisc code path.
816 flush_scheduled_work();
818 mutex_lock(&tty
->ldisc_mutex
);
820 * Now kill off the ldisc
822 tty_ldisc_close(tty
, tty
->ldisc
);
823 tty_ldisc_put(tty
->ldisc
);
824 /* Force an oops if we mess this up */
827 /* Ensure the next open requests the N_TTY ldisc */
828 tty_set_termios_ldisc(tty
, N_TTY
);
829 mutex_unlock(&tty
->ldisc_mutex
);
831 /* This will need doing differently if we need to lock */
833 tty_ldisc_release(o_tty
, NULL
);
835 /* And the memory resources remaining (buffers, termios) will be
836 disposed of when the kref hits zero */
840 * tty_ldisc_init - ldisc setup for new tty
841 * @tty: tty being allocated
843 * Set up the line discipline objects for a newly allocated tty. Note that
844 * the tty structure is not completely set up when this call is made.
847 void tty_ldisc_init(struct tty_struct
*tty
)
849 struct tty_ldisc
*ld
= tty_ldisc_get(N_TTY
);
851 panic("n_tty: init_tty");
852 tty_ldisc_assign(tty
, ld
);
855 void tty_ldisc_begin(void)
857 /* Setup the default TTY line discipline. */
858 (void) tty_register_ldisc(N_TTY
, &tty_ldisc_N_TTY
);