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>
  8#include <linux/tty.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>
 16#include <linux/kd.h>
 17#include <linux/mm.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>
 29
 30#include <linux/uaccess.h>
 31#include <asm/system.h>
 32
 33#include <linux/kbd_kern.h>
 34#include <linux/vt_kern.h>
 35#include <linux/selection.h>
 
 
 
 
 
 
 
 
 
 
 
 
 
 36
 37#include <linux/kmod.h>
 38#include <linux/nsproxy.h>
 39
 40/*
 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.
 44 */
 45
 46static DEFINE_SPINLOCK(tty_ldisc_lock);
 47static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
 48static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
 49/* Line disc dispatch table */
 50static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
 51
 52static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
 53{
 54	if (ld)
 55		atomic_inc(&ld->users);
 56	return ld;
 57}
 58
 59static void put_ldisc(struct tty_ldisc *ld)
 60{
 61	unsigned long flags;
 62
 63	if (WARN_ON_ONCE(!ld))
 64		return;
 65
 66	/*
 67	 * If this is the last user, free the ldisc, and
 68	 * release the ldisc ops.
 69	 *
 70	 * We really want an "atomic_dec_and_lock_irqsave()",
 71	 * but we don't have it, so this does it by hand.
 72	 */
 73	local_irq_save(flags);
 74	if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
 75		struct tty_ldisc_ops *ldo = ld->ops;
 76
 77		ldo->refcount--;
 78		module_put(ldo->owner);
 79		spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 80
 81		kfree(ld);
 82		return;
 83	}
 84	local_irq_restore(flags);
 85	wake_up(&tty_ldisc_idle);
 86}
 87
 88/**
 89 *	tty_register_ldisc	-	install a line discipline
 90 *	@disc: ldisc number
 91 *	@new_ldisc: pointer to the ldisc object
 92 *
 93 *	Installs a new line discipline into the kernel. The discipline
 94 *	is set up as unreferenced and then made available to the kernel
 95 *	from this point onwards.
 96 *
 97 *	Locking:
 98 *		takes tty_ldisc_lock to guard against ldisc races
 99 */
100
101int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
102{
103	unsigned long flags;
104	int ret = 0;
105
106	if (disc < N_TTY || disc >= NR_LDISCS)
107		return -EINVAL;
108
109	spin_lock_irqsave(&tty_ldisc_lock, flags);
110	tty_ldiscs[disc] = new_ldisc;
111	new_ldisc->num = disc;
112	new_ldisc->refcount = 0;
113	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
114
115	return ret;
116}
117EXPORT_SYMBOL(tty_register_ldisc);
118
119/**
120 *	tty_unregister_ldisc	-	unload a line discipline
121 *	@disc: ldisc number
122 *	@new_ldisc: pointer to the ldisc object
123 *
124 *	Remove a line discipline from the kernel providing it is not
125 *	currently in use.
126 *
127 *	Locking:
128 *		takes tty_ldisc_lock to guard against ldisc races
129 */
130
131int tty_unregister_ldisc(int disc)
132{
133	unsigned long flags;
134	int ret = 0;
135
136	if (disc < N_TTY || disc >= NR_LDISCS)
137		return -EINVAL;
138
139	spin_lock_irqsave(&tty_ldisc_lock, flags);
140	if (tty_ldiscs[disc]->refcount)
141		ret = -EBUSY;
142	else
143		tty_ldiscs[disc] = NULL;
144	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
145
146	return ret;
147}
148EXPORT_SYMBOL(tty_unregister_ldisc);
149
150static struct tty_ldisc_ops *get_ldops(int disc)
151{
152	unsigned long flags;
153	struct tty_ldisc_ops *ldops, *ret;
154
155	spin_lock_irqsave(&tty_ldisc_lock, flags);
156	ret = ERR_PTR(-EINVAL);
157	ldops = tty_ldiscs[disc];
158	if (ldops) {
159		ret = ERR_PTR(-EAGAIN);
160		if (try_module_get(ldops->owner)) {
161			ldops->refcount++;
162			ret = ldops;
163		}
164	}
165	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
166	return ret;
167}
168
169static void put_ldops(struct tty_ldisc_ops *ldops)
170{
171	unsigned long flags;
172
173	spin_lock_irqsave(&tty_ldisc_lock, flags);
174	ldops->refcount--;
175	module_put(ldops->owner);
176	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
177}
178
179/**
180 *	tty_ldisc_get		-	take a reference to an ldisc
181 *	@disc: ldisc number
182 *
183 *	Takes a reference to a line discipline. Deals with refcounts and
184 *	module locking counts. Returns NULL if the discipline is not available.
185 *	Returns a pointer to the discipline and bumps the ref count if it is
186 *	available
187 *
188 *	Locking:
189 *		takes tty_ldisc_lock to guard against ldisc races
190 */
191
192static struct tty_ldisc *tty_ldisc_get(int disc)
193{
194	struct tty_ldisc *ld;
195	struct tty_ldisc_ops *ldops;
196
197	if (disc < N_TTY || disc >= NR_LDISCS)
198		return ERR_PTR(-EINVAL);
199
200	/*
201	 * Get the ldisc ops - we may need to request them to be loaded
202	 * dynamically and try again.
203	 */
204	ldops = get_ldops(disc);
205	if (IS_ERR(ldops)) {
206		request_module("tty-ldisc-%d", disc);
207		ldops = get_ldops(disc);
208		if (IS_ERR(ldops))
209			return ERR_CAST(ldops);
210	}
211
212	ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
213	if (ld == NULL) {
214		put_ldops(ldops);
215		return ERR_PTR(-ENOMEM);
216	}
217
218	ld->ops = ldops;
219	atomic_set(&ld->users, 1);
 
220	return ld;
221}
222
 
 
 
 
 
 
 
 
 
 
 
 
 
 
223static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
224{
225	return (*pos < NR_LDISCS) ? pos : NULL;
226}
227
228static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
229{
230	(*pos)++;
231	return (*pos < NR_LDISCS) ? pos : NULL;
232}
233
234static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
235{
236}
237
238static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
239{
240	int i = *(loff_t *)v;
241	struct tty_ldisc_ops *ldops;
242
243	ldops = get_ldops(i);
244	if (IS_ERR(ldops))
245		return 0;
246	seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
247	put_ldops(ldops);
248	return 0;
249}
250
251static const struct seq_operations tty_ldiscs_seq_ops = {
252	.start	= tty_ldiscs_seq_start,
253	.next	= tty_ldiscs_seq_next,
254	.stop	= tty_ldiscs_seq_stop,
255	.show	= tty_ldiscs_seq_show,
256};
257
258static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
259{
260	return seq_open(file, &tty_ldiscs_seq_ops);
261}
262
263const struct file_operations tty_ldiscs_proc_fops = {
264	.owner		= THIS_MODULE,
265	.open		= proc_tty_ldiscs_open,
266	.read		= seq_read,
267	.llseek		= seq_lseek,
268	.release	= seq_release,
269};
270
271/**
272 *	tty_ldisc_assign	-	set ldisc on a tty
273 *	@tty: tty to assign
274 *	@ld: line discipline
275 *
276 *	Install an instance of a line discipline into a tty structure. The
277 *	ldisc must have a reference count above zero to ensure it remains.
278 *	The tty instance refcount starts at zero.
279 *
280 *	Locking:
281 *		Caller must hold references
282 */
283
284static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
285{
286	tty->ldisc = ld;
287}
288
289/**
290 *	tty_ldisc_try		-	internal helper
291 *	@tty: the tty
292 *
293 *	Make a single attempt to grab and bump the refcount on
294 *	the tty ldisc. Return 0 on failure or 1 on success. This is
295 *	used to implement both the waiting and non waiting versions
296 *	of tty_ldisc_ref
297 *
298 *	Locking: takes tty_ldisc_lock
299 */
300
301static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
302{
303	unsigned long flags;
304	struct tty_ldisc *ld;
305
306	spin_lock_irqsave(&tty_ldisc_lock, flags);
307	ld = NULL;
308	if (test_bit(TTY_LDISC, &tty->flags))
309		ld = get_ldisc(tty->ldisc);
310	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
311	return ld;
312}
313
314/**
315 *	tty_ldisc_ref_wait	-	wait for the tty ldisc
316 *	@tty: tty device
317 *
318 *	Dereference the line discipline for the terminal and take a
319 *	reference to it. If the line discipline is in flux then
320 *	wait patiently until it changes.
321 *
322 *	Note: Must not be called from an IRQ/timer context. The caller
323 *	must also be careful not to hold other locks that will deadlock
324 *	against a discipline change, such as an existing ldisc reference
325 *	(which we check for)
326 *
327 *	Locking: call functions take tty_ldisc_lock
 
328 */
329
330struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
331{
332	struct tty_ldisc *ld;
333
334	/* wait_event is a macro */
335	wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
336	return ld;
337}
338EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
339
340/**
341 *	tty_ldisc_ref		-	get the tty ldisc
342 *	@tty: tty device
343 *
344 *	Dereference the line discipline for the terminal and take a
345 *	reference to it. If the line discipline is in flux then
346 *	return NULL. Can be called from IRQ and timer functions.
347 *
348 *	Locking: called functions take tty_ldisc_lock
349 */
350
351struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
352{
353	return tty_ldisc_try(tty);
 
 
 
 
 
 
 
354}
355EXPORT_SYMBOL_GPL(tty_ldisc_ref);
356
357/**
358 *	tty_ldisc_deref		-	free a tty ldisc reference
359 *	@ld: reference to free up
360 *
361 *	Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
362 *	be called in IRQ context.
363 *
364 *	Locking: takes tty_ldisc_lock
365 */
366
367void tty_ldisc_deref(struct tty_ldisc *ld)
368{
369	put_ldisc(ld);
370}
371EXPORT_SYMBOL_GPL(tty_ldisc_deref);
372
373static inline void tty_ldisc_put(struct tty_ldisc *ld)
 
 
374{
375	put_ldisc(ld);
376}
377
378/**
379 *	tty_ldisc_enable	-	allow ldisc use
380 *	@tty: terminal to activate ldisc on
381 *
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.
385 *
386 *	Note: nobody should set the TTY_LDISC bit except via this function.
387 *	Clearing directly is allowed.
388 */
389
390void tty_ldisc_enable(struct tty_struct *tty)
391{
392	set_bit(TTY_LDISC, &tty->flags);
393	clear_bit(TTY_LDISC_CHANGING, &tty->flags);
394	wake_up(&tty_ldisc_wait);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
395}
396
397/**
398 *	tty_ldisc_flush	-	flush line discipline queue
399 *	@tty: tty
400 *
401 *	Flush the line discipline queue (if any) for this tty. If there
402 *	is no line discipline active this is a no-op.
403 */
404
405void tty_ldisc_flush(struct tty_struct *tty)
406{
407	struct tty_ldisc *ld = tty_ldisc_ref(tty);
408	if (ld) {
409		if (ld->ops->flush_buffer)
410			ld->ops->flush_buffer(tty);
411		tty_ldisc_deref(ld);
412	}
413	tty_buffer_flush(tty);
414}
415EXPORT_SYMBOL_GPL(tty_ldisc_flush);
416
417/**
418 *	tty_set_termios_ldisc		-	set ldisc field
419 *	@tty: tty structure
420 *	@num: line discipline number
421 *
422 *	This is probably overkill for real world processors but
423 *	they are not on hot paths so a little discipline won't do
424 *	any harm.
425 *
426 *	Locking: takes termios_mutex
427 */
428
429static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
430{
431	mutex_lock(&tty->termios_mutex);
432	tty->termios->c_line = num;
433	mutex_unlock(&tty->termios_mutex);
434}
435
436/**
437 *	tty_ldisc_open		-	open a line discipline
438 *	@tty: tty we are opening the ldisc on
439 *	@ld: discipline to open
440 *
441 *	A helper opening method. Also a convenient debugging and check
442 *	point.
443 *
444 *	Locking: always called with BTM already held.
445 */
446
447static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
448{
449	WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
450	if (ld->ops->open) {
451		int ret;
452                /* BTM here locks versus a hangup event */
453		WARN_ON(!tty_locked());
454		ret = ld->ops->open(tty);
455		if (ret)
456			clear_bit(TTY_LDISC_OPEN, &tty->flags);
457		return ret;
458	}
459	return 0;
460}
461
462/**
463 *	tty_ldisc_close		-	close a line discipline
464 *	@tty: tty we are opening the ldisc on
465 *	@ld: discipline to close
466 *
467 *	A helper close method. Also a convenient debugging and check
468 *	point.
469 */
470
471static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
472{
473	WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
474	clear_bit(TTY_LDISC_OPEN, &tty->flags);
475	if (ld->ops->close)
476		ld->ops->close(tty);
477}
478
479/**
480 *	tty_ldisc_restore	-	helper for tty ldisc change
481 *	@tty: tty to recover
482 *	@old: previous ldisc
483 *
484 *	Restore the previous line discipline or N_TTY when a line discipline
485 *	change fails due to an open error
486 */
487
488static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
489{
490	char buf[64];
491	struct tty_ldisc *new_ldisc;
492	int r;
493
494	/* There is an outstanding reference here so this is safe */
495	old = tty_ldisc_get(old->ops->num);
496	WARN_ON(IS_ERR(old));
497	tty_ldisc_assign(tty, old);
498	tty_set_termios_ldisc(tty, old->ops->num);
499	if (tty_ldisc_open(tty, old) < 0) {
500		tty_ldisc_put(old);
501		/* This driver is always present */
502		new_ldisc = tty_ldisc_get(N_TTY);
503		if (IS_ERR(new_ldisc))
504			panic("n_tty: get");
505		tty_ldisc_assign(tty, new_ldisc);
506		tty_set_termios_ldisc(tty, N_TTY);
507		r = tty_ldisc_open(tty, new_ldisc);
508		if (r < 0)
509			panic("Couldn't open N_TTY ldisc for "
510			      "%s --- error %d.",
511			      tty_name(tty, buf), r);
512	}
513}
514
515/**
516 *	tty_ldisc_halt		-	shut down the line discipline
517 *	@tty: tty device
518 *
519 *	Shut down the line discipline and work queue for this tty device.
520 *	The TTY_LDISC flag being cleared ensures no further references can
521 *	be obtained while the delayed work queue halt ensures that no more
522 *	data is fed to the ldisc.
523 *
524 *	You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
525 *	in order to make sure any currently executing ldisc work is also
526 *	flushed.
527 */
528
529static int tty_ldisc_halt(struct tty_struct *tty)
530{
531	clear_bit(TTY_LDISC, &tty->flags);
532	return cancel_work_sync(&tty->buf.work);
533}
534
535/**
536 *	tty_ldisc_flush_works	-	flush all works of a tty
537 *	@tty: tty device to flush works for
538 *
539 *	Sync flush all works belonging to @tty.
540 */
541static void tty_ldisc_flush_works(struct tty_struct *tty)
542{
543	flush_work_sync(&tty->hangup_work);
544	flush_work_sync(&tty->SAK_work);
545	flush_work_sync(&tty->buf.work);
546}
547
548/**
549 *	tty_ldisc_wait_idle	-	wait for the ldisc to become idle
550 *	@tty: tty to wait for
551 *
552 *	Wait for the line discipline to become idle. The discipline must
553 *	have been halted for this to guarantee it remains idle.
554 */
555static int tty_ldisc_wait_idle(struct tty_struct *tty)
556{
557	int ret;
558	ret = wait_event_timeout(tty_ldisc_idle,
559			atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
560	if (ret < 0)
561		return ret;
562	return ret > 0 ? 0 : -EBUSY;
563}
564
565/**
566 *	tty_set_ldisc		-	set line discipline
567 *	@tty: the terminal to set
568 *	@ldisc: the line discipline
569 *
570 *	Set the discipline of a tty line. Must be called from a process
571 *	context. The ldisc change logic has to protect itself against any
572 *	overlapping ldisc change (including on the other end of pty pairs),
573 *	the close of one side of a tty/pty pair, and eventually hangup.
574 *
575 *	Locking: takes tty_ldisc_lock, termios_mutex
576 */
577
578int tty_set_ldisc(struct tty_struct *tty, int ldisc)
579{
580	int retval;
581	struct tty_ldisc *o_ldisc, *new_ldisc;
582	int work, o_work = 0;
583	struct tty_struct *o_tty;
584
585	new_ldisc = tty_ldisc_get(ldisc);
586	if (IS_ERR(new_ldisc))
587		return PTR_ERR(new_ldisc);
588
589	tty_lock();
590	/*
591	 *	We need to look at the tty locking here for pty/tty pairs
592	 *	when both sides try to change in parallel.
593	 */
594
595	o_tty = tty->link;	/* o_tty is the pty side or NULL */
596
597
598	/*
599	 *	Check the no-op case
600	 */
601
602	if (tty->ldisc->ops->num == ldisc) {
603		tty_unlock();
604		tty_ldisc_put(new_ldisc);
605		return 0;
606	}
607
608	tty_unlock();
609	/*
610	 *	Problem: What do we do if this blocks ?
611	 *	We could deadlock here
612	 */
613
614	tty_wait_until_sent(tty, 0);
615
616	tty_lock();
617	mutex_lock(&tty->ldisc_mutex);
618
619	/*
620	 *	We could be midstream of another ldisc change which has
621	 *	dropped the lock during processing. If so we need to wait.
622	 */
623
624	while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
625		mutex_unlock(&tty->ldisc_mutex);
626		tty_unlock();
627		wait_event(tty_ldisc_wait,
628			test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
629		tty_lock();
630		mutex_lock(&tty->ldisc_mutex);
631	}
632
633	set_bit(TTY_LDISC_CHANGING, &tty->flags);
634
635	/*
636	 *	No more input please, we are switching. The new ldisc
637	 *	will update this value in the ldisc open function
638	 */
639
640	tty->receive_room = 0;
641
642	o_ldisc = tty->ldisc;
643
644	tty_unlock();
645	/*
646	 *	Make sure we don't change while someone holds a
647	 *	reference to the line discipline. The TTY_LDISC bit
648	 *	prevents anyone taking a reference once it is clear.
649	 *	We need the lock to avoid racing reference takers.
650	 *
651	 *	We must clear the TTY_LDISC bit here to avoid a livelock
652	 *	with a userspace app continually trying to use the tty in
653	 *	parallel to the change and re-referencing the tty.
654	 */
655
656	work = tty_ldisc_halt(tty);
657	if (o_tty)
658		o_work = tty_ldisc_halt(o_tty);
659
660	/*
661	 * Wait for ->hangup_work and ->buf.work handlers to terminate.
662	 * We must drop the mutex here in case a hangup is also in process.
663	 */
664
665	mutex_unlock(&tty->ldisc_mutex);
666
667	tty_ldisc_flush_works(tty);
668
669	retval = tty_ldisc_wait_idle(tty);
670
671	tty_lock();
672	mutex_lock(&tty->ldisc_mutex);
673
674	/* handle wait idle failure locked */
675	if (retval) {
676		tty_ldisc_put(new_ldisc);
677		goto enable;
678	}
679
680	if (test_bit(TTY_HUPPED, &tty->flags)) {
681		/* We were raced by the hangup method. It will have stomped
682		   the ldisc data and closed the ldisc down */
683		clear_bit(TTY_LDISC_CHANGING, &tty->flags);
684		mutex_unlock(&tty->ldisc_mutex);
685		tty_ldisc_put(new_ldisc);
686		tty_unlock();
687		return -EIO;
688	}
689
690	/* Shutdown the current discipline. */
691	tty_ldisc_close(tty, o_ldisc);
692
693	/* Now set up the new line discipline. */
694	tty_ldisc_assign(tty, new_ldisc);
695	tty_set_termios_ldisc(tty, ldisc);
696
697	retval = tty_ldisc_open(tty, new_ldisc);
698	if (retval < 0) {
699		/* Back to the old one or N_TTY if we can't */
700		tty_ldisc_put(new_ldisc);
701		tty_ldisc_restore(tty, o_ldisc);
702	}
703
704	/* At this point we hold a reference to the new ldisc and a
705	   a reference to the old ldisc. If we ended up flipping back
706	   to the existing ldisc we have two references to it */
707
708	if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
709		tty->ops->set_ldisc(tty);
710
711	tty_ldisc_put(o_ldisc);
 
 
 
 
 
 
712
713enable:
714	/*
715	 *	Allow ldisc referencing to occur again
716	 */
717
718	tty_ldisc_enable(tty);
719	if (o_tty)
720		tty_ldisc_enable(o_tty);
721
722	/* Restart the work queue in case no characters kick it off. Safe if
723	   already running */
724	if (work)
725		schedule_work(&tty->buf.work);
726	if (o_work)
727		schedule_work(&o_tty->buf.work);
728	mutex_unlock(&tty->ldisc_mutex);
729	tty_unlock();
730	return retval;
731}
732
733/**
734 *	tty_reset_termios	-	reset terminal state
735 *	@tty: tty to reset
736 *
737 *	Restore a terminal to the driver default state.
738 */
739
740static void tty_reset_termios(struct tty_struct *tty)
741{
742	mutex_lock(&tty->termios_mutex);
743	*tty->termios = tty->driver->init_termios;
744	tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
745	tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
746	mutex_unlock(&tty->termios_mutex);
747}
748
749
750/**
751 *	tty_ldisc_reinit	-	reinitialise the tty ldisc
752 *	@tty: tty to reinit
753 *	@ldisc: line discipline to reinitialize
754 *
755 *	Switch the tty to a line discipline and leave the ldisc
756 *	state closed
757 */
758
759static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
760{
761	struct tty_ldisc *ld = tty_ldisc_get(ldisc);
762
763	if (IS_ERR(ld))
764		return -1;
765
766	WARN_ON_ONCE(tty_ldisc_wait_idle(tty));
767
768	tty_ldisc_close(tty, tty->ldisc);
769	tty_ldisc_put(tty->ldisc);
770	tty->ldisc = NULL;
771	/*
772	 *	Switch the line discipline back
773	 */
774	tty_ldisc_assign(tty, ld);
775	tty_set_termios_ldisc(tty, ldisc);
776
777	return 0;
778}
779
780/**
781 *	tty_ldisc_hangup		-	hangup ldisc reset
782 *	@tty: tty being hung up
783 *
784 *	Some tty devices reset their termios when they receive a hangup
785 *	event. In that situation we must also switch back to N_TTY properly
786 *	before we reset the termios data.
787 *
788 *	Locking: We can take the ldisc mutex as the rest of the code is
789 *	careful to allow for this.
790 *
791 *	In the pty pair case this occurs in the close() path of the
792 *	tty itself so we must be careful about locking rules.
793 */
794
795void tty_ldisc_hangup(struct tty_struct *tty)
796{
797	struct tty_ldisc *ld;
798	int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
799	int err = 0;
800
801	/*
802	 * FIXME! What are the locking issues here? This may me overdoing
803	 * things... This question is especially important now that we've
804	 * removed the irqlock.
805	 */
806	ld = tty_ldisc_ref(tty);
807	if (ld != NULL) {
808		/* We may have no line discipline at this point */
809		if (ld->ops->flush_buffer)
810			ld->ops->flush_buffer(tty);
811		tty_driver_flush_buffer(tty);
812		if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
813		    ld->ops->write_wakeup)
814			ld->ops->write_wakeup(tty);
815		if (ld->ops->hangup)
816			ld->ops->hangup(tty);
817		tty_ldisc_deref(ld);
818	}
819	/*
820	 * FIXME: Once we trust the LDISC code better we can wait here for
821	 * ldisc completion and fix the driver call race
822	 */
823	wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
824	wake_up_interruptible_poll(&tty->read_wait, POLLIN);
 
 
 
825	/*
826	 * Shutdown the current line discipline, and reset it to
827	 * N_TTY if need be.
828	 *
829	 * Avoid racing set_ldisc or tty_ldisc_release
830	 */
831	mutex_lock(&tty->ldisc_mutex);
 
832
833	/*
834	 * this is like tty_ldisc_halt, but we need to give up
835	 * the BTM before calling cancel_work_sync, which may
836	 * need to wait for another function taking the BTM
837	 */
838	clear_bit(TTY_LDISC, &tty->flags);
839	tty_unlock();
840	cancel_work_sync(&tty->buf.work);
841	mutex_unlock(&tty->ldisc_mutex);
842
843	tty_lock();
844	mutex_lock(&tty->ldisc_mutex);
845
846	/* At this point we have a closed ldisc and we want to
847	   reopen it. We could defer this to the next open but
848	   it means auditing a lot of other paths so this is
849	   a FIXME */
850	if (tty->ldisc) {	/* Not yet closed */
851		if (reset == 0) {
852
853			if (!tty_ldisc_reinit(tty, tty->termios->c_line))
854				err = tty_ldisc_open(tty, tty->ldisc);
855			else
856				err = 1;
857		}
858		/* If the re-open fails or we reset then go to N_TTY. The
859		   N_TTY open cannot fail */
860		if (reset || err) {
861			BUG_ON(tty_ldisc_reinit(tty, N_TTY));
862			WARN_ON(tty_ldisc_open(tty, tty->ldisc));
863		}
864		tty_ldisc_enable(tty);
865	}
866	mutex_unlock(&tty->ldisc_mutex);
867	if (reset)
868		tty_reset_termios(tty);
 
 
869}
870
871/**
872 *	tty_ldisc_setup			-	open line discipline
873 *	@tty: tty being shut down
874 *	@o_tty: pair tty for pty/tty pairs
875 *
876 *	Called during the initial open of a tty/pty pair in order to set up the
877 *	line disciplines and bind them to the tty. This has no locking issues
878 *	as the device isn't yet active.
879 */
880
881int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
882{
883	struct tty_ldisc *ld = tty->ldisc;
884	int retval;
885
886	retval = tty_ldisc_open(tty, ld);
887	if (retval)
888		return retval;
889
890	if (o_tty) {
891		retval = tty_ldisc_open(o_tty, o_tty->ldisc);
892		if (retval) {
893			tty_ldisc_close(tty, ld);
894			return retval;
895		}
896		tty_ldisc_enable(o_tty);
897	}
898	tty_ldisc_enable(tty);
899	return 0;
900}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
901/**
902 *	tty_ldisc_release		-	release line discipline
903 *	@tty: tty being shut down
904 *	@o_tty: pair tty for pty/tty pairs
905 *
906 *	Called during the final close of a tty/pty pair in order to shut down
907 *	the line discpline layer. On exit the ldisc assigned is N_TTY and the
908 *	ldisc has not been opened.
909 */
910
911void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
912{
913	/*
914	 * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
915	 * kill any delayed work. As this is the final close it does not
916	 * race with the set_ldisc code path.
917	 */
918
919	tty_unlock();
920	tty_ldisc_halt(tty);
921	tty_ldisc_flush_works(tty);
922	tty_lock();
923
924	mutex_lock(&tty->ldisc_mutex);
925	/*
926	 * Now kill off the ldisc
927	 */
928	tty_ldisc_close(tty, tty->ldisc);
929	tty_ldisc_put(tty->ldisc);
930	/* Force an oops if we mess this up */
931	tty->ldisc = NULL;
932
933	/* Ensure the next open requests the N_TTY ldisc */
934	tty_set_termios_ldisc(tty, N_TTY);
935	mutex_unlock(&tty->ldisc_mutex);
936
937	/* This will need doing differently if we need to lock */
938	if (o_tty)
939		tty_ldisc_release(o_tty, NULL);
 
 
 
940
941	/* And the memory resources remaining (buffers, termios) will be
942	   disposed of when the kref hits zero */
 
 
943}
944
945/**
946 *	tty_ldisc_init		-	ldisc setup for new tty
947 *	@tty: tty being allocated
948 *
949 *	Set up the line discipline objects for a newly allocated tty. Note that
950 *	the tty structure is not completely set up when this call is made.
951 */
952
953void tty_ldisc_init(struct tty_struct *tty)
954{
955	struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
956	if (IS_ERR(ld))
957		panic("n_tty: init_tty");
958	tty_ldisc_assign(tty, ld);
959}
960
961/**
962 *	tty_ldisc_init		-	ldisc cleanup for new tty
963 *	@tty: tty that was allocated recently
964 *
965 *	The tty structure must not becompletely set up (tty_ldisc_setup) when
966 *      this call is made.
967 */
968void tty_ldisc_deinit(struct tty_struct *tty)
969{
970	put_ldisc(tty->ldisc);
971	tty_ldisc_assign(tty, NULL);
972}
973
974void tty_ldisc_begin(void)
975{
976	/* Setup the default TTY line discipline. */
977	(void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
978}