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
);