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>
23 * This guards the refcounted line discipline lists. The lock
24 * must be taken with irqs off because there are hangup path
25 * callers who will do ldisc lookups and cannot sleep.
28 static DEFINE_SPINLOCK(tty_ldisc_lock
);
29 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait
);
30 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle
);
31 /* Line disc dispatch table */
32 static struct tty_ldisc_ops
*tty_ldiscs
[NR_LDISCS
];
34 static inline struct tty_ldisc
*get_ldisc(struct tty_ldisc
*ld
)
37 atomic_inc(&ld
->users
);
41 static void put_ldisc(struct tty_ldisc
*ld
)
45 if (WARN_ON_ONCE(!ld
))
49 * If this is the last user, free the ldisc, and
50 * release the ldisc ops.
52 * We really want an "atomic_dec_and_lock_irqsave()",
53 * but we don't have it, so this does it by hand.
55 local_irq_save(flags
);
56 if (atomic_dec_and_lock(&ld
->users
, &tty_ldisc_lock
)) {
57 struct tty_ldisc_ops
*ldo
= ld
->ops
;
60 module_put(ldo
->owner
);
61 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
66 local_irq_restore(flags
);
67 wake_up(&tty_ldisc_idle
);
71 * tty_register_ldisc - install a line discipline
73 * @new_ldisc: pointer to the ldisc object
75 * Installs a new line discipline into the kernel. The discipline
76 * is set up as unreferenced and then made available to the kernel
77 * from this point onwards.
80 * takes tty_ldisc_lock to guard against ldisc races
83 int tty_register_ldisc(int disc
, struct tty_ldisc_ops
*new_ldisc
)
88 if (disc
< N_TTY
|| disc
>= NR_LDISCS
)
91 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
92 tty_ldiscs
[disc
] = new_ldisc
;
93 new_ldisc
->num
= disc
;
94 new_ldisc
->refcount
= 0;
95 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
99 EXPORT_SYMBOL(tty_register_ldisc
);
102 * tty_unregister_ldisc - unload a line discipline
103 * @disc: ldisc number
104 * @new_ldisc: pointer to the ldisc object
106 * Remove a line discipline from the kernel providing it is not
110 * takes tty_ldisc_lock to guard against ldisc races
113 int tty_unregister_ldisc(int disc
)
118 if (disc
< N_TTY
|| disc
>= NR_LDISCS
)
121 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
122 if (tty_ldiscs
[disc
]->refcount
)
125 tty_ldiscs
[disc
] = NULL
;
126 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
130 EXPORT_SYMBOL(tty_unregister_ldisc
);
132 static struct tty_ldisc_ops
*get_ldops(int disc
)
135 struct tty_ldisc_ops
*ldops
, *ret
;
137 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
138 ret
= ERR_PTR(-EINVAL
);
139 ldops
= tty_ldiscs
[disc
];
141 ret
= ERR_PTR(-EAGAIN
);
142 if (try_module_get(ldops
->owner
)) {
147 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
151 static void put_ldops(struct tty_ldisc_ops
*ldops
)
155 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
157 module_put(ldops
->owner
);
158 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
162 * tty_ldisc_get - take a reference to an ldisc
163 * @disc: ldisc number
165 * Takes a reference to a line discipline. Deals with refcounts and
166 * module locking counts. Returns NULL if the discipline is not available.
167 * Returns a pointer to the discipline and bumps the ref count if it is
171 * takes tty_ldisc_lock to guard against ldisc races
174 static struct tty_ldisc
*tty_ldisc_get(int disc
)
176 struct tty_ldisc
*ld
;
177 struct tty_ldisc_ops
*ldops
;
179 if (disc
< N_TTY
|| disc
>= NR_LDISCS
)
180 return ERR_PTR(-EINVAL
);
183 * Get the ldisc ops - we may need to request them to be loaded
184 * dynamically and try again.
186 ldops
= get_ldops(disc
);
188 request_module("tty-ldisc-%d", disc
);
189 ldops
= get_ldops(disc
);
191 return ERR_CAST(ldops
);
194 ld
= kmalloc(sizeof(struct tty_ldisc
), GFP_KERNEL
);
197 return ERR_PTR(-ENOMEM
);
201 atomic_set(&ld
->users
, 1);
205 static void *tty_ldiscs_seq_start(struct seq_file
*m
, loff_t
*pos
)
207 return (*pos
< NR_LDISCS
) ? pos
: NULL
;
210 static void *tty_ldiscs_seq_next(struct seq_file
*m
, void *v
, loff_t
*pos
)
213 return (*pos
< NR_LDISCS
) ? pos
: NULL
;
216 static void tty_ldiscs_seq_stop(struct seq_file
*m
, void *v
)
220 static int tty_ldiscs_seq_show(struct seq_file
*m
, void *v
)
222 int i
= *(loff_t
*)v
;
223 struct tty_ldisc_ops
*ldops
;
225 ldops
= get_ldops(i
);
228 seq_printf(m
, "%-10s %2d\n", ldops
->name
? ldops
->name
: "???", i
);
233 static const struct seq_operations tty_ldiscs_seq_ops
= {
234 .start
= tty_ldiscs_seq_start
,
235 .next
= tty_ldiscs_seq_next
,
236 .stop
= tty_ldiscs_seq_stop
,
237 .show
= tty_ldiscs_seq_show
,
240 static int proc_tty_ldiscs_open(struct inode
*inode
, struct file
*file
)
242 return seq_open(file
, &tty_ldiscs_seq_ops
);
245 const struct file_operations tty_ldiscs_proc_fops
= {
246 .owner
= THIS_MODULE
,
247 .open
= proc_tty_ldiscs_open
,
250 .release
= seq_release
,
254 * tty_ldisc_assign - set ldisc on a tty
255 * @tty: tty to assign
256 * @ld: line discipline
258 * Install an instance of a line discipline into a tty structure. The
259 * ldisc must have a reference count above zero to ensure it remains.
260 * The tty instance refcount starts at zero.
263 * Caller must hold references
266 static void tty_ldisc_assign(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
272 * tty_ldisc_try - internal helper
275 * Make a single attempt to grab and bump the refcount on
276 * the tty ldisc. Return 0 on failure or 1 on success. This is
277 * used to implement both the waiting and non waiting versions
280 * Locking: takes tty_ldisc_lock
283 static struct tty_ldisc
*tty_ldisc_try(struct tty_struct
*tty
)
286 struct tty_ldisc
*ld
;
288 spin_lock_irqsave(&tty_ldisc_lock
, flags
);
290 if (test_bit(TTY_LDISC
, &tty
->flags
))
291 ld
= get_ldisc(tty
->ldisc
);
292 spin_unlock_irqrestore(&tty_ldisc_lock
, flags
);
297 * tty_ldisc_ref_wait - wait for the tty ldisc
300 * Dereference the line discipline for the terminal and take a
301 * reference to it. If the line discipline is in flux then
302 * wait patiently until it changes.
304 * Note: Must not be called from an IRQ/timer context. The caller
305 * must also be careful not to hold other locks that will deadlock
306 * against a discipline change, such as an existing ldisc reference
307 * (which we check for)
309 * Locking: call functions take tty_ldisc_lock
312 struct tty_ldisc
*tty_ldisc_ref_wait(struct tty_struct
*tty
)
314 struct tty_ldisc
*ld
;
316 /* wait_event is a macro */
317 wait_event(tty_ldisc_wait
, (ld
= tty_ldisc_try(tty
)) != NULL
);
320 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait
);
323 * tty_ldisc_ref - get the tty ldisc
326 * Dereference the line discipline for the terminal and take a
327 * reference to it. If the line discipline is in flux then
328 * return NULL. Can be called from IRQ and timer functions.
330 * Locking: called functions take tty_ldisc_lock
333 struct tty_ldisc
*tty_ldisc_ref(struct tty_struct
*tty
)
335 return tty_ldisc_try(tty
);
337 EXPORT_SYMBOL_GPL(tty_ldisc_ref
);
340 * tty_ldisc_deref - free a tty ldisc reference
341 * @ld: reference to free up
343 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
344 * be called in IRQ context.
346 * Locking: takes tty_ldisc_lock
349 void tty_ldisc_deref(struct tty_ldisc
*ld
)
353 EXPORT_SYMBOL_GPL(tty_ldisc_deref
);
355 static inline void tty_ldisc_put(struct tty_ldisc
*ld
)
361 * tty_ldisc_enable - allow ldisc use
362 * @tty: terminal to activate ldisc on
364 * Set the TTY_LDISC flag when the line discipline can be called
365 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
366 * changing flag to indicate any ldisc change is now over.
368 * Note: nobody should set the TTY_LDISC bit except via this function.
369 * Clearing directly is allowed.
372 void tty_ldisc_enable(struct tty_struct
*tty
)
374 set_bit(TTY_LDISC
, &tty
->flags
);
375 clear_bit(TTY_LDISC_CHANGING
, &tty
->flags
);
376 wake_up(&tty_ldisc_wait
);
380 * tty_ldisc_flush - flush line discipline queue
383 * Flush the line discipline queue (if any) for this tty. If there
384 * is no line discipline active this is a no-op.
387 void tty_ldisc_flush(struct tty_struct
*tty
)
389 struct tty_ldisc
*ld
= tty_ldisc_ref(tty
);
391 if (ld
->ops
->flush_buffer
)
392 ld
->ops
->flush_buffer(tty
);
395 tty_buffer_flush(tty
);
397 EXPORT_SYMBOL_GPL(tty_ldisc_flush
);
400 * tty_set_termios_ldisc - set ldisc field
401 * @tty: tty structure
402 * @num: line discipline number
404 * This is probably overkill for real world processors but
405 * they are not on hot paths so a little discipline won't do
408 * Locking: takes termios_mutex
411 static void tty_set_termios_ldisc(struct tty_struct
*tty
, int num
)
413 mutex_lock(&tty
->termios_mutex
);
414 tty
->termios
->c_line
= num
;
415 mutex_unlock(&tty
->termios_mutex
);
419 * tty_ldisc_open - open a line discipline
420 * @tty: tty we are opening the ldisc on
421 * @ld: discipline to open
423 * A helper opening method. Also a convenient debugging and check
426 * Locking: always called with BTM already held.
429 static int tty_ldisc_open(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
431 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN
, &tty
->flags
));
434 /* BTM here locks versus a hangup event */
435 ret
= ld
->ops
->open(tty
);
437 clear_bit(TTY_LDISC_OPEN
, &tty
->flags
);
444 * tty_ldisc_close - close a line discipline
445 * @tty: tty we are opening the ldisc on
446 * @ld: discipline to close
448 * A helper close method. Also a convenient debugging and check
452 static void tty_ldisc_close(struct tty_struct
*tty
, struct tty_ldisc
*ld
)
454 WARN_ON(!test_bit(TTY_LDISC_OPEN
, &tty
->flags
));
455 clear_bit(TTY_LDISC_OPEN
, &tty
->flags
);
461 * tty_ldisc_restore - helper for tty ldisc change
462 * @tty: tty to recover
463 * @old: previous ldisc
465 * Restore the previous line discipline or N_TTY when a line discipline
466 * change fails due to an open error
469 static void tty_ldisc_restore(struct tty_struct
*tty
, struct tty_ldisc
*old
)
472 struct tty_ldisc
*new_ldisc
;
475 /* There is an outstanding reference here so this is safe */
476 old
= tty_ldisc_get(old
->ops
->num
);
477 WARN_ON(IS_ERR(old
));
478 tty_ldisc_assign(tty
, old
);
479 tty_set_termios_ldisc(tty
, old
->ops
->num
);
480 if (tty_ldisc_open(tty
, old
) < 0) {
482 /* This driver is always present */
483 new_ldisc
= tty_ldisc_get(N_TTY
);
484 if (IS_ERR(new_ldisc
))
486 tty_ldisc_assign(tty
, new_ldisc
);
487 tty_set_termios_ldisc(tty
, N_TTY
);
488 r
= tty_ldisc_open(tty
, new_ldisc
);
490 panic("Couldn't open N_TTY ldisc for "
492 tty_name(tty
, buf
), r
);
497 * tty_ldisc_halt - shut down the line discipline
500 * Shut down the line discipline and work queue for this tty device.
501 * The TTY_LDISC flag being cleared ensures no further references can
502 * be obtained while the delayed work queue halt ensures that no more
503 * data is fed to the ldisc.
505 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
506 * in order to make sure any currently executing ldisc work is also
510 static int tty_ldisc_halt(struct tty_struct
*tty
)
512 clear_bit(TTY_LDISC
, &tty
->flags
);
513 return cancel_work_sync(&tty
->buf
.work
);
517 * tty_ldisc_flush_works - flush all works of a tty
518 * @tty: tty device to flush works for
520 * Sync flush all works belonging to @tty.
522 static void tty_ldisc_flush_works(struct tty_struct
*tty
)
524 flush_work_sync(&tty
->hangup_work
);
525 flush_work_sync(&tty
->SAK_work
);
526 flush_work_sync(&tty
->buf
.work
);
530 * tty_ldisc_wait_idle - wait for the ldisc to become idle
531 * @tty: tty to wait for
533 * Wait for the line discipline to become idle. The discipline must
534 * have been halted for this to guarantee it remains idle.
536 static int tty_ldisc_wait_idle(struct tty_struct
*tty
)
539 ret
= wait_event_timeout(tty_ldisc_idle
,
540 atomic_read(&tty
->ldisc
->users
) == 1, 5 * HZ
);
541 return ret
> 0 ? 0 : -EBUSY
;
545 * tty_set_ldisc - set line discipline
546 * @tty: the terminal to set
547 * @ldisc: the line discipline
549 * Set the discipline of a tty line. Must be called from a process
550 * context. The ldisc change logic has to protect itself against any
551 * overlapping ldisc change (including on the other end of pty pairs),
552 * the close of one side of a tty/pty pair, and eventually hangup.
554 * Locking: takes tty_ldisc_lock, termios_mutex
557 int tty_set_ldisc(struct tty_struct
*tty
, int ldisc
)
560 struct tty_ldisc
*o_ldisc
, *new_ldisc
;
561 int work
, o_work
= 0;
562 struct tty_struct
*o_tty
;
564 new_ldisc
= tty_ldisc_get(ldisc
);
565 if (IS_ERR(new_ldisc
))
566 return PTR_ERR(new_ldisc
);
570 * We need to look at the tty locking here for pty/tty pairs
571 * when both sides try to change in parallel.
574 o_tty
= tty
->link
; /* o_tty is the pty side or NULL */
578 * Check the no-op case
581 if (tty
->ldisc
->ops
->num
== ldisc
) {
583 tty_ldisc_put(new_ldisc
);
589 * Problem: What do we do if this blocks ?
590 * We could deadlock here
593 tty_wait_until_sent(tty
, 0);
596 mutex_lock(&tty
->ldisc_mutex
);
599 * We could be midstream of another ldisc change which has
600 * dropped the lock during processing. If so we need to wait.
603 while (test_bit(TTY_LDISC_CHANGING
, &tty
->flags
)) {
604 mutex_unlock(&tty
->ldisc_mutex
);
606 wait_event(tty_ldisc_wait
,
607 test_bit(TTY_LDISC_CHANGING
, &tty
->flags
) == 0);
609 mutex_lock(&tty
->ldisc_mutex
);
612 set_bit(TTY_LDISC_CHANGING
, &tty
->flags
);
615 * No more input please, we are switching. The new ldisc
616 * will update this value in the ldisc open function
619 tty
->receive_room
= 0;
621 o_ldisc
= tty
->ldisc
;
625 * Make sure we don't change while someone holds a
626 * reference to the line discipline. The TTY_LDISC bit
627 * prevents anyone taking a reference once it is clear.
628 * We need the lock to avoid racing reference takers.
630 * We must clear the TTY_LDISC bit here to avoid a livelock
631 * with a userspace app continually trying to use the tty in
632 * parallel to the change and re-referencing the tty.
635 work
= tty_ldisc_halt(tty
);
637 o_work
= tty_ldisc_halt(o_tty
);
640 * Wait for ->hangup_work and ->buf.work handlers to terminate.
641 * We must drop the mutex here in case a hangup is also in process.
644 mutex_unlock(&tty
->ldisc_mutex
);
646 tty_ldisc_flush_works(tty
);
648 retval
= tty_ldisc_wait_idle(tty
);
651 mutex_lock(&tty
->ldisc_mutex
);
653 /* handle wait idle failure locked */
655 tty_ldisc_put(new_ldisc
);
659 if (test_bit(TTY_HUPPED
, &tty
->flags
)) {
660 /* We were raced by the hangup method. It will have stomped
661 the ldisc data and closed the ldisc down */
662 clear_bit(TTY_LDISC_CHANGING
, &tty
->flags
);
663 mutex_unlock(&tty
->ldisc_mutex
);
664 tty_ldisc_put(new_ldisc
);
669 /* Shutdown the current discipline. */
670 tty_ldisc_close(tty
, o_ldisc
);
672 /* Now set up the new line discipline. */
673 tty_ldisc_assign(tty
, new_ldisc
);
674 tty_set_termios_ldisc(tty
, ldisc
);
676 retval
= tty_ldisc_open(tty
, new_ldisc
);
678 /* Back to the old one or N_TTY if we can't */
679 tty_ldisc_put(new_ldisc
);
680 tty_ldisc_restore(tty
, o_ldisc
);
683 /* At this point we hold a reference to the new ldisc and a
684 a reference to the old ldisc. If we ended up flipping back
685 to the existing ldisc we have two references to it */
687 if (tty
->ldisc
->ops
->num
!= o_ldisc
->ops
->num
&& tty
->ops
->set_ldisc
)
688 tty
->ops
->set_ldisc(tty
);
690 tty_ldisc_put(o_ldisc
);
694 * Allow ldisc referencing to occur again
697 tty_ldisc_enable(tty
);
699 tty_ldisc_enable(o_tty
);
701 /* Restart the work queue in case no characters kick it off. Safe if
704 schedule_work(&tty
->buf
.work
);
706 schedule_work(&o_tty
->buf
.work
);
707 mutex_unlock(&tty
->ldisc_mutex
);
713 * tty_reset_termios - reset terminal state
716 * Restore a terminal to the driver default state.
719 static void tty_reset_termios(struct tty_struct
*tty
)
721 mutex_lock(&tty
->termios_mutex
);
722 *tty
->termios
= tty
->driver
->init_termios
;
723 tty
->termios
->c_ispeed
= tty_termios_input_baud_rate(tty
->termios
);
724 tty
->termios
->c_ospeed
= tty_termios_baud_rate(tty
->termios
);
725 mutex_unlock(&tty
->termios_mutex
);
730 * tty_ldisc_reinit - reinitialise the tty ldisc
731 * @tty: tty to reinit
732 * @ldisc: line discipline to reinitialize
734 * Switch the tty to a line discipline and leave the ldisc
738 static int tty_ldisc_reinit(struct tty_struct
*tty
, int ldisc
)
740 struct tty_ldisc
*ld
= tty_ldisc_get(ldisc
);
745 WARN_ON_ONCE(tty_ldisc_wait_idle(tty
));
747 tty_ldisc_close(tty
, tty
->ldisc
);
748 tty_ldisc_put(tty
->ldisc
);
751 * Switch the line discipline back
753 tty_ldisc_assign(tty
, ld
);
754 tty_set_termios_ldisc(tty
, ldisc
);
760 * tty_ldisc_hangup - hangup ldisc reset
761 * @tty: tty being hung up
763 * Some tty devices reset their termios when they receive a hangup
764 * event. In that situation we must also switch back to N_TTY properly
765 * before we reset the termios data.
767 * Locking: We can take the ldisc mutex as the rest of the code is
768 * careful to allow for this.
770 * In the pty pair case this occurs in the close() path of the
771 * tty itself so we must be careful about locking rules.
774 void tty_ldisc_hangup(struct tty_struct
*tty
)
776 struct tty_ldisc
*ld
;
777 int reset
= tty
->driver
->flags
& TTY_DRIVER_RESET_TERMIOS
;
781 * FIXME! What are the locking issues here? This may me overdoing
782 * things... This question is especially important now that we've
783 * removed the irqlock.
785 ld
= tty_ldisc_ref(tty
);
787 /* We may have no line discipline at this point */
788 if (ld
->ops
->flush_buffer
)
789 ld
->ops
->flush_buffer(tty
);
790 tty_driver_flush_buffer(tty
);
791 if ((test_bit(TTY_DO_WRITE_WAKEUP
, &tty
->flags
)) &&
792 ld
->ops
->write_wakeup
)
793 ld
->ops
->write_wakeup(tty
);
795 ld
->ops
->hangup(tty
);
799 * FIXME: Once we trust the LDISC code better we can wait here for
800 * ldisc completion and fix the driver call race
802 wake_up_interruptible_poll(&tty
->write_wait
, POLLOUT
);
803 wake_up_interruptible_poll(&tty
->read_wait
, POLLIN
);
805 * Shutdown the current line discipline, and reset it to
808 * Avoid racing set_ldisc or tty_ldisc_release
810 mutex_lock(&tty
->ldisc_mutex
);
813 * this is like tty_ldisc_halt, but we need to give up
814 * the BTM before calling cancel_work_sync, which may
815 * need to wait for another function taking the BTM
817 clear_bit(TTY_LDISC
, &tty
->flags
);
819 cancel_work_sync(&tty
->buf
.work
);
820 mutex_unlock(&tty
->ldisc_mutex
);
823 mutex_lock(&tty
->ldisc_mutex
);
825 /* At this point we have a closed ldisc and we want to
826 reopen it. We could defer this to the next open but
827 it means auditing a lot of other paths so this is
829 if (tty
->ldisc
) { /* Not yet closed */
832 if (!tty_ldisc_reinit(tty
, tty
->termios
->c_line
))
833 err
= tty_ldisc_open(tty
, tty
->ldisc
);
837 /* If the re-open fails or we reset then go to N_TTY. The
838 N_TTY open cannot fail */
840 BUG_ON(tty_ldisc_reinit(tty
, N_TTY
));
841 WARN_ON(tty_ldisc_open(tty
, tty
->ldisc
));
843 tty_ldisc_enable(tty
);
845 mutex_unlock(&tty
->ldisc_mutex
);
847 tty_reset_termios(tty
);
851 * tty_ldisc_setup - open line discipline
852 * @tty: tty being shut down
853 * @o_tty: pair tty for pty/tty pairs
855 * Called during the initial open of a tty/pty pair in order to set up the
856 * line disciplines and bind them to the tty. This has no locking issues
857 * as the device isn't yet active.
860 int tty_ldisc_setup(struct tty_struct
*tty
, struct tty_struct
*o_tty
)
862 struct tty_ldisc
*ld
= tty
->ldisc
;
865 retval
= tty_ldisc_open(tty
, ld
);
870 retval
= tty_ldisc_open(o_tty
, o_tty
->ldisc
);
872 tty_ldisc_close(tty
, ld
);
875 tty_ldisc_enable(o_tty
);
877 tty_ldisc_enable(tty
);
881 * tty_ldisc_release - release line discipline
882 * @tty: tty being shut down
883 * @o_tty: pair tty for pty/tty pairs
885 * Called during the final close of a tty/pty pair in order to shut down
886 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
887 * ldisc has not been opened.
890 void tty_ldisc_release(struct tty_struct
*tty
, struct tty_struct
*o_tty
)
893 * Prevent flush_to_ldisc() from rescheduling the work for later. Then
894 * kill any delayed work. As this is the final close it does not
895 * race with the set_ldisc code path.
900 tty_ldisc_flush_works(tty
);
903 mutex_lock(&tty
->ldisc_mutex
);
905 * Now kill off the ldisc
907 tty_ldisc_close(tty
, tty
->ldisc
);
908 tty_ldisc_put(tty
->ldisc
);
909 /* Force an oops if we mess this up */
912 /* Ensure the next open requests the N_TTY ldisc */
913 tty_set_termios_ldisc(tty
, N_TTY
);
914 mutex_unlock(&tty
->ldisc_mutex
);
916 /* This will need doing differently if we need to lock */
918 tty_ldisc_release(o_tty
, NULL
);
920 /* And the memory resources remaining (buffers, termios) will be
921 disposed of when the kref hits zero */
925 * tty_ldisc_init - ldisc setup for new tty
926 * @tty: tty being allocated
928 * Set up the line discipline objects for a newly allocated tty. Note that
929 * the tty structure is not completely set up when this call is made.
932 void tty_ldisc_init(struct tty_struct
*tty
)
934 struct tty_ldisc
*ld
= tty_ldisc_get(N_TTY
);
936 panic("n_tty: init_tty");
937 tty_ldisc_assign(tty
, ld
);
941 * tty_ldisc_init - ldisc cleanup for new tty
942 * @tty: tty that was allocated recently
944 * The tty structure must not becompletely set up (tty_ldisc_setup) when
947 void tty_ldisc_deinit(struct tty_struct
*tty
)
949 put_ldisc(tty
->ldisc
);
950 tty_ldisc_assign(tty
, NULL
);
953 void tty_ldisc_begin(void)
955 /* Setup the default TTY line discipline. */
956 (void) tty_register_ldisc(N_TTY
, &tty_ldisc_N_TTY
);