Root/drivers/tty/tty_ldisc.c

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>
6#include <linux/tty.h>
7#include <linux/tty_driver.h>
8#include <linux/file.h>
9#include <linux/mm.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>
21#include <linux/ratelimit.h>
22
23/*
24 * This guards the refcounted line discipline lists. The lock
25 * must be taken with irqs off because there are hangup path
26 * callers who will do ldisc lookups and cannot sleep.
27 */
28
29static DEFINE_RAW_SPINLOCK(tty_ldisc_lock);
30static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
31/* Line disc dispatch table */
32static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
33
34static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
35{
36    if (ld)
37        atomic_inc(&ld->users);
38    return ld;
39}
40
41static void put_ldisc(struct tty_ldisc *ld)
42{
43    unsigned long flags;
44
45    if (WARN_ON_ONCE(!ld))
46        return;
47
48    /*
49     * If this is the last user, free the ldisc, and
50     * release the ldisc ops.
51     *
52     * We really want an "atomic_dec_and_raw_lock_irqsave()",
53     * but we don't have it, so this does it by hand.
54     */
55    raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
56    if (atomic_dec_and_test(&ld->users)) {
57        struct tty_ldisc_ops *ldo = ld->ops;
58
59        ldo->refcount--;
60        module_put(ldo->owner);
61        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
62
63        kfree(ld);
64        return;
65    }
66    raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
67
68    if (waitqueue_active(&ld->wq_idle))
69        wake_up(&ld->wq_idle);
70}
71
72/**
73 * tty_register_ldisc - install a line discipline
74 * @disc: ldisc number
75 * @new_ldisc: pointer to the ldisc object
76 *
77 * Installs a new line discipline into the kernel. The discipline
78 * is set up as unreferenced and then made available to the kernel
79 * from this point onwards.
80 *
81 * Locking:
82 * takes tty_ldisc_lock to guard against ldisc races
83 */
84
85int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
86{
87    unsigned long flags;
88    int ret = 0;
89
90    if (disc < N_TTY || disc >= NR_LDISCS)
91        return -EINVAL;
92
93    raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
94    tty_ldiscs[disc] = new_ldisc;
95    new_ldisc->num = disc;
96    new_ldisc->refcount = 0;
97    raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
98
99    return ret;
100}
101EXPORT_SYMBOL(tty_register_ldisc);
102
103/**
104 * tty_unregister_ldisc - unload a line discipline
105 * @disc: ldisc number
106 * @new_ldisc: pointer to the ldisc object
107 *
108 * Remove a line discipline from the kernel providing it is not
109 * currently in use.
110 *
111 * Locking:
112 * takes tty_ldisc_lock to guard against ldisc races
113 */
114
115int tty_unregister_ldisc(int disc)
116{
117    unsigned long flags;
118    int ret = 0;
119
120    if (disc < N_TTY || disc >= NR_LDISCS)
121        return -EINVAL;
122
123    raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
124    if (tty_ldiscs[disc]->refcount)
125        ret = -EBUSY;
126    else
127        tty_ldiscs[disc] = NULL;
128    raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
129
130    return ret;
131}
132EXPORT_SYMBOL(tty_unregister_ldisc);
133
134static struct tty_ldisc_ops *get_ldops(int disc)
135{
136    unsigned long flags;
137    struct tty_ldisc_ops *ldops, *ret;
138
139    raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
140    ret = ERR_PTR(-EINVAL);
141    ldops = tty_ldiscs[disc];
142    if (ldops) {
143        ret = ERR_PTR(-EAGAIN);
144        if (try_module_get(ldops->owner)) {
145            ldops->refcount++;
146            ret = ldops;
147        }
148    }
149    raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
150    return ret;
151}
152
153static void put_ldops(struct tty_ldisc_ops *ldops)
154{
155    unsigned long flags;
156
157    raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
158    ldops->refcount--;
159    module_put(ldops->owner);
160    raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
161}
162
163/**
164 * tty_ldisc_get - take a reference to an ldisc
165 * @disc: ldisc number
166 *
167 * Takes a reference to a line discipline. Deals with refcounts and
168 * module locking counts. Returns NULL if the discipline is not available.
169 * Returns a pointer to the discipline and bumps the ref count if it is
170 * available
171 *
172 * Locking:
173 * takes tty_ldisc_lock to guard against ldisc races
174 */
175
176static struct tty_ldisc *tty_ldisc_get(int disc)
177{
178    struct tty_ldisc *ld;
179    struct tty_ldisc_ops *ldops;
180
181    if (disc < N_TTY || disc >= NR_LDISCS)
182        return ERR_PTR(-EINVAL);
183
184    /*
185     * Get the ldisc ops - we may need to request them to be loaded
186     * dynamically and try again.
187     */
188    ldops = get_ldops(disc);
189    if (IS_ERR(ldops)) {
190        request_module("tty-ldisc-%d", disc);
191        ldops = get_ldops(disc);
192        if (IS_ERR(ldops))
193            return ERR_CAST(ldops);
194    }
195
196    ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
197    if (ld == NULL) {
198        put_ldops(ldops);
199        return ERR_PTR(-ENOMEM);
200    }
201
202    ld->ops = ldops;
203    atomic_set(&ld->users, 1);
204    init_waitqueue_head(&ld->wq_idle);
205
206    return ld;
207}
208
209static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
210{
211    return (*pos < NR_LDISCS) ? pos : NULL;
212}
213
214static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
215{
216    (*pos)++;
217    return (*pos < NR_LDISCS) ? pos : NULL;
218}
219
220static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
221{
222}
223
224static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
225{
226    int i = *(loff_t *)v;
227    struct tty_ldisc_ops *ldops;
228
229    ldops = get_ldops(i);
230    if (IS_ERR(ldops))
231        return 0;
232    seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
233    put_ldops(ldops);
234    return 0;
235}
236
237static const struct seq_operations tty_ldiscs_seq_ops = {
238    .start = tty_ldiscs_seq_start,
239    .next = tty_ldiscs_seq_next,
240    .stop = tty_ldiscs_seq_stop,
241    .show = tty_ldiscs_seq_show,
242};
243
244static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
245{
246    return seq_open(file, &tty_ldiscs_seq_ops);
247}
248
249const struct file_operations tty_ldiscs_proc_fops = {
250    .owner = THIS_MODULE,
251    .open = proc_tty_ldiscs_open,
252    .read = seq_read,
253    .llseek = seq_lseek,
254    .release = seq_release,
255};
256
257/**
258 * tty_ldisc_assign - set ldisc on a tty
259 * @tty: tty to assign
260 * @ld: line discipline
261 *
262 * Install an instance of a line discipline into a tty structure. The
263 * ldisc must have a reference count above zero to ensure it remains.
264 * The tty instance refcount starts at zero.
265 *
266 * Locking:
267 * Caller must hold references
268 */
269
270static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
271{
272    tty->ldisc = ld;
273}
274
275/**
276 * tty_ldisc_try - internal helper
277 * @tty: the tty
278 *
279 * Make a single attempt to grab and bump the refcount on
280 * the tty ldisc. Return 0 on failure or 1 on success. This is
281 * used to implement both the waiting and non waiting versions
282 * of tty_ldisc_ref
283 *
284 * Locking: takes tty_ldisc_lock
285 */
286
287static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
288{
289    unsigned long flags;
290    struct tty_ldisc *ld;
291
292    raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
293    ld = NULL;
294    if (test_bit(TTY_LDISC, &tty->flags))
295        ld = get_ldisc(tty->ldisc);
296    raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
297    return ld;
298}
299
300/**
301 * tty_ldisc_ref_wait - wait for the tty ldisc
302 * @tty: tty device
303 *
304 * Dereference the line discipline for the terminal and take a
305 * reference to it. If the line discipline is in flux then
306 * wait patiently until it changes.
307 *
308 * Note: Must not be called from an IRQ/timer context. The caller
309 * must also be careful not to hold other locks that will deadlock
310 * against a discipline change, such as an existing ldisc reference
311 * (which we check for)
312 *
313 * Locking: call functions take tty_ldisc_lock
314 */
315
316struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
317{
318    struct tty_ldisc *ld;
319
320    /* wait_event is a macro */
321    wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
322    return ld;
323}
324EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
325
326/**
327 * tty_ldisc_ref - get the tty ldisc
328 * @tty: tty device
329 *
330 * Dereference the line discipline for the terminal and take a
331 * reference to it. If the line discipline is in flux then
332 * return NULL. Can be called from IRQ and timer functions.
333 *
334 * Locking: called functions take tty_ldisc_lock
335 */
336
337struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
338{
339    return tty_ldisc_try(tty);
340}
341EXPORT_SYMBOL_GPL(tty_ldisc_ref);
342
343/**
344 * tty_ldisc_deref - free a tty ldisc reference
345 * @ld: reference to free up
346 *
347 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
348 * be called in IRQ context.
349 *
350 * Locking: takes tty_ldisc_lock
351 */
352
353void tty_ldisc_deref(struct tty_ldisc *ld)
354{
355    put_ldisc(ld);
356}
357EXPORT_SYMBOL_GPL(tty_ldisc_deref);
358
359static inline void tty_ldisc_put(struct tty_ldisc *ld)
360{
361    put_ldisc(ld);
362}
363
364/**
365 * tty_ldisc_enable - allow ldisc use
366 * @tty: terminal to activate ldisc on
367 *
368 * Set the TTY_LDISC flag when the line discipline can be called
369 * again. Do necessary wakeups for existing sleepers. Clear the LDISC
370 * changing flag to indicate any ldisc change is now over.
371 *
372 * Note: nobody should set the TTY_LDISC bit except via this function.
373 * Clearing directly is allowed.
374 */
375
376void tty_ldisc_enable(struct tty_struct *tty)
377{
378    set_bit(TTY_LDISC, &tty->flags);
379    clear_bit(TTY_LDISC_CHANGING, &tty->flags);
380    wake_up(&tty_ldisc_wait);
381}
382
383/**
384 * tty_ldisc_flush - flush line discipline queue
385 * @tty: tty
386 *
387 * Flush the line discipline queue (if any) for this tty. If there
388 * is no line discipline active this is a no-op.
389 */
390
391void tty_ldisc_flush(struct tty_struct *tty)
392{
393    struct tty_ldisc *ld = tty_ldisc_ref(tty);
394    if (ld) {
395        if (ld->ops->flush_buffer)
396            ld->ops->flush_buffer(tty);
397        tty_ldisc_deref(ld);
398    }
399    tty_buffer_flush(tty);
400}
401EXPORT_SYMBOL_GPL(tty_ldisc_flush);
402
403/**
404 * tty_set_termios_ldisc - set ldisc field
405 * @tty: tty structure
406 * @num: line discipline number
407 *
408 * This is probably overkill for real world processors but
409 * they are not on hot paths so a little discipline won't do
410 * any harm.
411 *
412 * Locking: takes termios_mutex
413 */
414
415static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
416{
417    mutex_lock(&tty->termios_mutex);
418    tty->termios.c_line = num;
419    mutex_unlock(&tty->termios_mutex);
420}
421
422/**
423 * tty_ldisc_open - open a line discipline
424 * @tty: tty we are opening the ldisc on
425 * @ld: discipline to open
426 *
427 * A helper opening method. Also a convenient debugging and check
428 * point.
429 *
430 * Locking: always called with BTM already held.
431 */
432
433static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
434{
435    WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
436    if (ld->ops->open) {
437        int ret;
438                /* BTM here locks versus a hangup event */
439        ret = ld->ops->open(tty);
440        if (ret)
441            clear_bit(TTY_LDISC_OPEN, &tty->flags);
442        return ret;
443    }
444    return 0;
445}
446
447/**
448 * tty_ldisc_close - close a line discipline
449 * @tty: tty we are opening the ldisc on
450 * @ld: discipline to close
451 *
452 * A helper close method. Also a convenient debugging and check
453 * point.
454 */
455
456static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
457{
458    WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
459    clear_bit(TTY_LDISC_OPEN, &tty->flags);
460    if (ld->ops->close)
461        ld->ops->close(tty);
462}
463
464/**
465 * tty_ldisc_restore - helper for tty ldisc change
466 * @tty: tty to recover
467 * @old: previous ldisc
468 *
469 * Restore the previous line discipline or N_TTY when a line discipline
470 * change fails due to an open error
471 */
472
473static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
474{
475    char buf[64];
476    struct tty_ldisc *new_ldisc;
477    int r;
478
479    /* There is an outstanding reference here so this is safe */
480    old = tty_ldisc_get(old->ops->num);
481    WARN_ON(IS_ERR(old));
482    tty_ldisc_assign(tty, old);
483    tty_set_termios_ldisc(tty, old->ops->num);
484    if (tty_ldisc_open(tty, old) < 0) {
485        tty_ldisc_put(old);
486        /* This driver is always present */
487        new_ldisc = tty_ldisc_get(N_TTY);
488        if (IS_ERR(new_ldisc))
489            panic("n_tty: get");
490        tty_ldisc_assign(tty, new_ldisc);
491        tty_set_termios_ldisc(tty, N_TTY);
492        r = tty_ldisc_open(tty, new_ldisc);
493        if (r < 0)
494            panic("Couldn't open N_TTY ldisc for "
495                  "%s --- error %d.",
496                  tty_name(tty, buf), r);
497    }
498}
499
500/**
501 * tty_ldisc_halt - shut down the line discipline
502 * @tty: tty device
503 *
504 * Shut down the line discipline and work queue for this tty device.
505 * The TTY_LDISC flag being cleared ensures no further references can
506 * be obtained while the delayed work queue halt ensures that no more
507 * data is fed to the ldisc.
508 *
509 * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
510 * in order to make sure any currently executing ldisc work is also
511 * flushed.
512 */
513
514static int tty_ldisc_halt(struct tty_struct *tty)
515{
516    clear_bit(TTY_LDISC, &tty->flags);
517    return cancel_work_sync(&tty->port->buf.work);
518}
519
520/**
521 * tty_ldisc_flush_works - flush all works of a tty
522 * @tty: tty device to flush works for
523 *
524 * Sync flush all works belonging to @tty.
525 */
526static void tty_ldisc_flush_works(struct tty_struct *tty)
527{
528    flush_work(&tty->hangup_work);
529    flush_work(&tty->SAK_work);
530    flush_work(&tty->port->buf.work);
531}
532
533/**
534 * tty_ldisc_wait_idle - wait for the ldisc to become idle
535 * @tty: tty to wait for
536 * @timeout: for how long to wait at most
537 *
538 * Wait for the line discipline to become idle. The discipline must
539 * have been halted for this to guarantee it remains idle.
540 */
541static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
542{
543    long ret;
544    ret = wait_event_timeout(tty->ldisc->wq_idle,
545            atomic_read(&tty->ldisc->users) == 1, timeout);
546    return ret > 0 ? 0 : -EBUSY;
547}
548
549/**
550 * tty_set_ldisc - set line discipline
551 * @tty: the terminal to set
552 * @ldisc: the line discipline
553 *
554 * Set the discipline of a tty line. Must be called from a process
555 * context. The ldisc change logic has to protect itself against any
556 * overlapping ldisc change (including on the other end of pty pairs),
557 * the close of one side of a tty/pty pair, and eventually hangup.
558 *
559 * Locking: takes tty_ldisc_lock, termios_mutex
560 */
561
562int tty_set_ldisc(struct tty_struct *tty, int ldisc)
563{
564    int retval;
565    struct tty_ldisc *o_ldisc, *new_ldisc;
566    int work, o_work = 0;
567    struct tty_struct *o_tty;
568
569    new_ldisc = tty_ldisc_get(ldisc);
570    if (IS_ERR(new_ldisc))
571        return PTR_ERR(new_ldisc);
572
573    tty_lock(tty);
574    /*
575     * We need to look at the tty locking here for pty/tty pairs
576     * when both sides try to change in parallel.
577     */
578
579    o_tty = tty->link; /* o_tty is the pty side or NULL */
580
581
582    /*
583     * Check the no-op case
584     */
585
586    if (tty->ldisc->ops->num == ldisc) {
587        tty_unlock(tty);
588        tty_ldisc_put(new_ldisc);
589        return 0;
590    }
591
592    tty_unlock(tty);
593    /*
594     * Problem: What do we do if this blocks ?
595     * We could deadlock here
596     */
597
598    tty_wait_until_sent(tty, 0);
599
600    tty_lock(tty);
601    mutex_lock(&tty->ldisc_mutex);
602
603    /*
604     * We could be midstream of another ldisc change which has
605     * dropped the lock during processing. If so we need to wait.
606     */
607
608    while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
609        mutex_unlock(&tty->ldisc_mutex);
610        tty_unlock(tty);
611        wait_event(tty_ldisc_wait,
612            test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
613        tty_lock(tty);
614        mutex_lock(&tty->ldisc_mutex);
615    }
616
617    set_bit(TTY_LDISC_CHANGING, &tty->flags);
618
619    /*
620     * No more input please, we are switching. The new ldisc
621     * will update this value in the ldisc open function
622     */
623
624    tty->receive_room = 0;
625
626    o_ldisc = tty->ldisc;
627
628    tty_unlock(tty);
629    /*
630     * Make sure we don't change while someone holds a
631     * reference to the line discipline. The TTY_LDISC bit
632     * prevents anyone taking a reference once it is clear.
633     * We need the lock to avoid racing reference takers.
634     *
635     * We must clear the TTY_LDISC bit here to avoid a livelock
636     * with a userspace app continually trying to use the tty in
637     * parallel to the change and re-referencing the tty.
638     */
639
640    work = tty_ldisc_halt(tty);
641    if (o_tty)
642        o_work = tty_ldisc_halt(o_tty);
643
644    /*
645     * Wait for ->hangup_work and ->buf.work handlers to terminate.
646     * We must drop the mutex here in case a hangup is also in process.
647     */
648
649    mutex_unlock(&tty->ldisc_mutex);
650
651    tty_ldisc_flush_works(tty);
652
653    retval = tty_ldisc_wait_idle(tty, 5 * HZ);
654
655    tty_lock(tty);
656    mutex_lock(&tty->ldisc_mutex);
657
658    /* handle wait idle failure locked */
659    if (retval) {
660        tty_ldisc_put(new_ldisc);
661        goto enable;
662    }
663
664    if (test_bit(TTY_HUPPING, &tty->flags)) {
665        /* We were raced by the hangup method. It will have stomped
666           the ldisc data and closed the ldisc down */
667        clear_bit(TTY_LDISC_CHANGING, &tty->flags);
668        mutex_unlock(&tty->ldisc_mutex);
669        tty_ldisc_put(new_ldisc);
670        tty_unlock(tty);
671        return -EIO;
672    }
673
674    /* Shutdown the current discipline. */
675    tty_ldisc_close(tty, o_ldisc);
676
677    /* Now set up the new line discipline. */
678    tty_ldisc_assign(tty, new_ldisc);
679    tty_set_termios_ldisc(tty, ldisc);
680
681    retval = tty_ldisc_open(tty, new_ldisc);
682    if (retval < 0) {
683        /* Back to the old one or N_TTY if we can't */
684        tty_ldisc_put(new_ldisc);
685        tty_ldisc_restore(tty, o_ldisc);
686    }
687
688    /* At this point we hold a reference to the new ldisc and a
689       a reference to the old ldisc. If we ended up flipping back
690       to the existing ldisc we have two references to it */
691
692    if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
693        tty->ops->set_ldisc(tty);
694
695    tty_ldisc_put(o_ldisc);
696
697enable:
698    /*
699     * Allow ldisc referencing to occur again
700     */
701
702    tty_ldisc_enable(tty);
703    if (o_tty)
704        tty_ldisc_enable(o_tty);
705
706    /* Restart the work queue in case no characters kick it off. Safe if
707       already running */
708    if (work)
709        schedule_work(&tty->port->buf.work);
710    if (o_work)
711        schedule_work(&o_tty->port->buf.work);
712    mutex_unlock(&tty->ldisc_mutex);
713    tty_unlock(tty);
714    return retval;
715}
716
717/**
718 * tty_reset_termios - reset terminal state
719 * @tty: tty to reset
720 *
721 * Restore a terminal to the driver default state.
722 */
723
724static void tty_reset_termios(struct tty_struct *tty)
725{
726    mutex_lock(&tty->termios_mutex);
727    tty->termios = tty->driver->init_termios;
728    tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
729    tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
730    mutex_unlock(&tty->termios_mutex);
731}
732
733
734/**
735 * tty_ldisc_reinit - reinitialise the tty ldisc
736 * @tty: tty to reinit
737 * @ldisc: line discipline to reinitialize
738 *
739 * Switch the tty to a line discipline and leave the ldisc
740 * state closed
741 */
742
743static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
744{
745    struct tty_ldisc *ld = tty_ldisc_get(ldisc);
746
747    if (IS_ERR(ld))
748        return -1;
749
750    tty_ldisc_close(tty, tty->ldisc);
751    tty_ldisc_put(tty->ldisc);
752    tty->ldisc = NULL;
753    /*
754     * Switch the line discipline back
755     */
756    tty_ldisc_assign(tty, ld);
757    tty_set_termios_ldisc(tty, ldisc);
758
759    return 0;
760}
761
762/**
763 * tty_ldisc_hangup - hangup ldisc reset
764 * @tty: tty being hung up
765 *
766 * Some tty devices reset their termios when they receive a hangup
767 * event. In that situation we must also switch back to N_TTY properly
768 * before we reset the termios data.
769 *
770 * Locking: We can take the ldisc mutex as the rest of the code is
771 * careful to allow for this.
772 *
773 * In the pty pair case this occurs in the close() path of the
774 * tty itself so we must be careful about locking rules.
775 */
776
777void tty_ldisc_hangup(struct tty_struct *tty)
778{
779    struct tty_ldisc *ld;
780    int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
781    int err = 0;
782
783    /*
784     * FIXME! What are the locking issues here? This may me overdoing
785     * things... This question is especially important now that we've
786     * removed the irqlock.
787     */
788    ld = tty_ldisc_ref(tty);
789    if (ld != NULL) {
790        /* We may have no line discipline at this point */
791        if (ld->ops->flush_buffer)
792            ld->ops->flush_buffer(tty);
793        tty_driver_flush_buffer(tty);
794        if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
795            ld->ops->write_wakeup)
796            ld->ops->write_wakeup(tty);
797        if (ld->ops->hangup)
798            ld->ops->hangup(tty);
799        tty_ldisc_deref(ld);
800    }
801    /*
802     * FIXME: Once we trust the LDISC code better we can wait here for
803     * ldisc completion and fix the driver call race
804     */
805    wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
806    wake_up_interruptible_poll(&tty->read_wait, POLLIN);
807    /*
808     * Shutdown the current line discipline, and reset it to
809     * N_TTY if need be.
810     *
811     * Avoid racing set_ldisc or tty_ldisc_release
812     */
813    mutex_lock(&tty->ldisc_mutex);
814
815    /*
816     * this is like tty_ldisc_halt, but we need to give up
817     * the BTM before calling cancel_work_sync, which may
818     * need to wait for another function taking the BTM
819     */
820    clear_bit(TTY_LDISC, &tty->flags);
821    tty_unlock(tty);
822    cancel_work_sync(&tty->port->buf.work);
823    mutex_unlock(&tty->ldisc_mutex);
824retry:
825    tty_lock(tty);
826    mutex_lock(&tty->ldisc_mutex);
827
828    /* At this point we have a closed ldisc and we want to
829       reopen it. We could defer this to the next open but
830       it means auditing a lot of other paths so this is
831       a FIXME */
832    if (tty->ldisc) { /* Not yet closed */
833        if (atomic_read(&tty->ldisc->users) != 1) {
834            char cur_n[TASK_COMM_LEN], tty_n[64];
835            long timeout = 3 * HZ;
836            tty_unlock(tty);
837
838            while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
839                timeout = MAX_SCHEDULE_TIMEOUT;
840                printk_ratelimited(KERN_WARNING
841                    "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
842                    __func__, get_task_comm(cur_n, current),
843                    tty_name(tty, tty_n));
844            }
845            mutex_unlock(&tty->ldisc_mutex);
846            goto retry;
847        }
848
849        if (reset == 0) {
850
851            if (!tty_ldisc_reinit(tty, tty->termios.c_line))
852                err = tty_ldisc_open(tty, tty->ldisc);
853            else
854                err = 1;
855        }
856        /* If the re-open fails or we reset then go to N_TTY. The
857           N_TTY open cannot fail */
858        if (reset || err) {
859            BUG_ON(tty_ldisc_reinit(tty, N_TTY));
860            WARN_ON(tty_ldisc_open(tty, tty->ldisc));
861        }
862        tty_ldisc_enable(tty);
863    }
864    mutex_unlock(&tty->ldisc_mutex);
865    if (reset)
866        tty_reset_termios(tty);
867}
868
869/**
870 * tty_ldisc_setup - open line discipline
871 * @tty: tty being shut down
872 * @o_tty: pair tty for pty/tty pairs
873 *
874 * Called during the initial open of a tty/pty pair in order to set up the
875 * line disciplines and bind them to the tty. This has no locking issues
876 * as the device isn't yet active.
877 */
878
879int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
880{
881    struct tty_ldisc *ld = tty->ldisc;
882    int retval;
883
884    retval = tty_ldisc_open(tty, ld);
885    if (retval)
886        return retval;
887
888    if (o_tty) {
889        retval = tty_ldisc_open(o_tty, o_tty->ldisc);
890        if (retval) {
891            tty_ldisc_close(tty, ld);
892            return retval;
893        }
894        tty_ldisc_enable(o_tty);
895    }
896    tty_ldisc_enable(tty);
897    return 0;
898}
899
900static void tty_ldisc_kill(struct tty_struct *tty)
901{
902    /* There cannot be users from userspace now. But there still might be
903     * drivers holding a reference via tty_ldisc_ref. Do not steal them the
904     * ldisc until they are done. */
905    tty_ldisc_wait_idle(tty, MAX_SCHEDULE_TIMEOUT);
906
907    mutex_lock(&tty->ldisc_mutex);
908    /*
909     * Now kill off the ldisc
910     */
911    tty_ldisc_close(tty, tty->ldisc);
912    tty_ldisc_put(tty->ldisc);
913    /* Force an oops if we mess this up */
914    tty->ldisc = NULL;
915
916    /* Ensure the next open requests the N_TTY ldisc */
917    tty_set_termios_ldisc(tty, N_TTY);
918    mutex_unlock(&tty->ldisc_mutex);
919}
920
921/**
922 * tty_ldisc_release - release line discipline
923 * @tty: tty being shut down
924 * @o_tty: pair tty for pty/tty pairs
925 *
926 * Called during the final close of a tty/pty pair in order to shut down
927 * the line discpline layer. On exit the ldisc assigned is N_TTY and the
928 * ldisc has not been opened.
929 */
930
931void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
932{
933    /*
934     * Prevent flush_to_ldisc() from rescheduling the work for later. Then
935     * kill any delayed work. As this is the final close it does not
936     * race with the set_ldisc code path.
937     */
938
939    tty_ldisc_halt(tty);
940    if (o_tty)
941        tty_ldisc_halt(o_tty);
942
943    tty_ldisc_flush_works(tty);
944    if (o_tty)
945        tty_ldisc_flush_works(o_tty);
946
947    tty_lock_pair(tty, o_tty);
948    /* This will need doing differently if we need to lock */
949    tty_ldisc_kill(tty);
950    if (o_tty)
951        tty_ldisc_kill(o_tty);
952
953    tty_unlock_pair(tty, o_tty);
954    /* And the memory resources remaining (buffers, termios) will be
955       disposed of when the kref hits zero */
956}
957
958/**
959 * tty_ldisc_init - ldisc setup for new tty
960 * @tty: tty being allocated
961 *
962 * Set up the line discipline objects for a newly allocated tty. Note that
963 * the tty structure is not completely set up when this call is made.
964 */
965
966void tty_ldisc_init(struct tty_struct *tty)
967{
968    struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
969    if (IS_ERR(ld))
970        panic("n_tty: init_tty");
971    tty_ldisc_assign(tty, ld);
972}
973
974/**
975 * tty_ldisc_init - ldisc cleanup for new tty
976 * @tty: tty that was allocated recently
977 *
978 * The tty structure must not becompletely set up (tty_ldisc_setup) when
979 * this call is made.
980 */
981void tty_ldisc_deinit(struct tty_struct *tty)
982{
983    put_ldisc(tty->ldisc);
984    tty_ldisc_assign(tty, NULL);
985}
986
987void tty_ldisc_begin(void)
988{
989    /* Setup the default TTY line discipline. */
990    (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
991}
992

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