1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * PPP synchronous tty channel driver for Linux.
4 *
5 * This is a ppp channel driver that can be used with tty device drivers
6 * that are frame oriented, such as synchronous HDLC devices.
7 *
8 * Complete PPP frames without encoding/decoding are exchanged between
9 * the channel driver and the device driver.
10 *
11 * The async map IOCTL codes are implemented to keep the user mode
12 * applications happy if they call them. Synchronous PPP does not use
13 * the async maps.
14 *
15 * Copyright 1999 Paul Mackerras.
16 *
17 * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
18 *
19 * This driver provides the encapsulation and framing for sending
20 * and receiving PPP frames over sync serial lines. It relies on
21 * the generic PPP layer to give it frames to send and to process
22 * received frames. It implements the PPP line discipline.
23 *
24 * Part of the code in this driver was inspired by the old async-only
25 * PPP driver, written by Michael Callahan and Al Longyear, and
26 * subsequently hacked by Paul Mackerras.
27 *
28 * ==FILEVERSION 20040616==
29 */
30
31 #include <linux/module.h>
32 #include <linux/kernel.h>
33 #include <linux/skbuff.h>
34 #include <linux/tty.h>
35 #include <linux/netdevice.h>
36 #include <linux/poll.h>
37 #include <linux/ppp_defs.h>
38 #include <linux/ppp-ioctl.h>
39 #include <linux/ppp_channel.h>
40 #include <linux/spinlock.h>
41 #include <linux/completion.h>
42 #include <linux/init.h>
43 #include <linux/interrupt.h>
44 #include <linux/slab.h>
45 #include <linux/refcount.h>
46 #include <asm/unaligned.h>
47 #include <linux/uaccess.h>
48
49 #define PPP_VERSION "2.4.2"
50
51 /* Structure for storing local state. */
52 struct syncppp {
53 struct tty_struct *tty;
54 unsigned int flags;
55 unsigned int rbits;
56 int mru;
57 spinlock_t xmit_lock;
58 spinlock_t recv_lock;
59 unsigned long xmit_flags;
60 u32 xaccm[8];
61 u32 raccm;
62 unsigned int bytes_sent;
63 unsigned int bytes_rcvd;
64
65 struct sk_buff *tpkt;
66 unsigned long last_xmit;
67
68 struct sk_buff_head rqueue;
69
70 struct tasklet_struct tsk;
71
72 refcount_t refcnt;
73 struct completion dead_cmp;
74 struct ppp_channel chan; /* interface to generic ppp layer */
75 };
76
77 /* Bit numbers in xmit_flags */
78 #define XMIT_WAKEUP 0
79 #define XMIT_FULL 1
80
81 /* Bits in rbits */
82 #define SC_RCV_BITS (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
83
84 #define PPPSYNC_MAX_RQLEN 32 /* arbitrary */
85
86 /*
87 * Prototypes.
88 */
89 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
90 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
91 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
92 unsigned long arg);
93 static void ppp_sync_process(struct tasklet_struct *t);
94 static int ppp_sync_push(struct syncppp *ap);
95 static void ppp_sync_flush_output(struct syncppp *ap);
96 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
97 char *flags, int count);
98
99 static const struct ppp_channel_ops sync_ops = {
100 .start_xmit = ppp_sync_send,
101 .ioctl = ppp_sync_ioctl,
102 };
103
104 /*
105 * Utility procedure to print a buffer in hex/ascii
106 */
107 static void
ppp_print_buffer(const char * name,const __u8 * buf,int count)108 ppp_print_buffer (const char *name, const __u8 *buf, int count)
109 {
110 if (name != NULL)
111 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
112
113 print_hex_dump_bytes("", DUMP_PREFIX_NONE, buf, count);
114 }
115
116
117 /*
118 * Routines implementing the synchronous PPP line discipline.
119 */
120
121 /*
122 * We have a potential race on dereferencing tty->disc_data,
123 * because the tty layer provides no locking at all - thus one
124 * cpu could be running ppp_synctty_receive while another
125 * calls ppp_synctty_close, which zeroes tty->disc_data and
126 * frees the memory that ppp_synctty_receive is using. The best
127 * way to fix this is to use a rwlock in the tty struct, but for now
128 * we use a single global rwlock for all ttys in ppp line discipline.
129 *
130 * FIXME: Fixed in tty_io nowadays.
131 */
132 static DEFINE_RWLOCK(disc_data_lock);
133
sp_get(struct tty_struct * tty)134 static struct syncppp *sp_get(struct tty_struct *tty)
135 {
136 struct syncppp *ap;
137
138 read_lock(&disc_data_lock);
139 ap = tty->disc_data;
140 if (ap != NULL)
141 refcount_inc(&ap->refcnt);
142 read_unlock(&disc_data_lock);
143 return ap;
144 }
145
sp_put(struct syncppp * ap)146 static void sp_put(struct syncppp *ap)
147 {
148 if (refcount_dec_and_test(&ap->refcnt))
149 complete(&ap->dead_cmp);
150 }
151
152 /*
153 * Called when a tty is put into sync-PPP line discipline.
154 */
155 static int
ppp_sync_open(struct tty_struct * tty)156 ppp_sync_open(struct tty_struct *tty)
157 {
158 struct syncppp *ap;
159 int err;
160 int speed;
161
162 if (tty->ops->write == NULL)
163 return -EOPNOTSUPP;
164
165 ap = kzalloc(sizeof(*ap), GFP_KERNEL);
166 err = -ENOMEM;
167 if (!ap)
168 goto out;
169
170 /* initialize the syncppp structure */
171 ap->tty = tty;
172 ap->mru = PPP_MRU;
173 spin_lock_init(&ap->xmit_lock);
174 spin_lock_init(&ap->recv_lock);
175 ap->xaccm[0] = ~0U;
176 ap->xaccm[3] = 0x60000000U;
177 ap->raccm = ~0U;
178
179 skb_queue_head_init(&ap->rqueue);
180 tasklet_setup(&ap->tsk, ppp_sync_process);
181
182 refcount_set(&ap->refcnt, 1);
183 init_completion(&ap->dead_cmp);
184
185 ap->chan.private = ap;
186 ap->chan.ops = &sync_ops;
187 ap->chan.mtu = PPP_MRU;
188 ap->chan.hdrlen = 2; /* for A/C bytes */
189 speed = tty_get_baud_rate(tty);
190 ap->chan.speed = speed;
191 err = ppp_register_channel(&ap->chan);
192 if (err)
193 goto out_free;
194
195 tty->disc_data = ap;
196 tty->receive_room = 65536;
197 return 0;
198
199 out_free:
200 kfree(ap);
201 out:
202 return err;
203 }
204
205 /*
206 * Called when the tty is put into another line discipline
207 * or it hangs up. We have to wait for any cpu currently
208 * executing in any of the other ppp_synctty_* routines to
209 * finish before we can call ppp_unregister_channel and free
210 * the syncppp struct. This routine must be called from
211 * process context, not interrupt or softirq context.
212 */
213 static void
ppp_sync_close(struct tty_struct * tty)214 ppp_sync_close(struct tty_struct *tty)
215 {
216 struct syncppp *ap;
217
218 write_lock_irq(&disc_data_lock);
219 ap = tty->disc_data;
220 tty->disc_data = NULL;
221 write_unlock_irq(&disc_data_lock);
222 if (!ap)
223 return;
224
225 /*
226 * We have now ensured that nobody can start using ap from now
227 * on, but we have to wait for all existing users to finish.
228 * Note that ppp_unregister_channel ensures that no calls to
229 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
230 * by the time it returns.
231 */
232 if (!refcount_dec_and_test(&ap->refcnt))
233 wait_for_completion(&ap->dead_cmp);
234 tasklet_kill(&ap->tsk);
235
236 ppp_unregister_channel(&ap->chan);
237 skb_queue_purge(&ap->rqueue);
238 kfree_skb(ap->tpkt);
239 kfree(ap);
240 }
241
242 /*
243 * Called on tty hangup in process context.
244 *
245 * Wait for I/O to driver to complete and unregister PPP channel.
246 * This is already done by the close routine, so just call that.
247 */
ppp_sync_hangup(struct tty_struct * tty)248 static int ppp_sync_hangup(struct tty_struct *tty)
249 {
250 ppp_sync_close(tty);
251 return 0;
252 }
253
254 /*
255 * Read does nothing - no data is ever available this way.
256 * Pppd reads and writes packets via /dev/ppp instead.
257 */
258 static ssize_t
ppp_sync_read(struct tty_struct * tty,struct file * file,unsigned char * buf,size_t count,void ** cookie,unsigned long offset)259 ppp_sync_read(struct tty_struct *tty, struct file *file,
260 unsigned char *buf, size_t count,
261 void **cookie, unsigned long offset)
262 {
263 return -EAGAIN;
264 }
265
266 /*
267 * Write on the tty does nothing, the packets all come in
268 * from the ppp generic stuff.
269 */
270 static ssize_t
ppp_sync_write(struct tty_struct * tty,struct file * file,const unsigned char * buf,size_t count)271 ppp_sync_write(struct tty_struct *tty, struct file *file,
272 const unsigned char *buf, size_t count)
273 {
274 return -EAGAIN;
275 }
276
277 static int
ppp_synctty_ioctl(struct tty_struct * tty,struct file * file,unsigned int cmd,unsigned long arg)278 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
279 unsigned int cmd, unsigned long arg)
280 {
281 struct syncppp *ap = sp_get(tty);
282 int __user *p = (int __user *)arg;
283 int err, val;
284
285 if (!ap)
286 return -ENXIO;
287 err = -EFAULT;
288 switch (cmd) {
289 case PPPIOCGCHAN:
290 err = -EFAULT;
291 if (put_user(ppp_channel_index(&ap->chan), p))
292 break;
293 err = 0;
294 break;
295
296 case PPPIOCGUNIT:
297 err = -EFAULT;
298 if (put_user(ppp_unit_number(&ap->chan), p))
299 break;
300 err = 0;
301 break;
302
303 case TCFLSH:
304 /* flush our buffers and the serial port's buffer */
305 if (arg == TCIOFLUSH || arg == TCOFLUSH)
306 ppp_sync_flush_output(ap);
307 err = n_tty_ioctl_helper(tty, file, cmd, arg);
308 break;
309
310 case FIONREAD:
311 val = 0;
312 if (put_user(val, p))
313 break;
314 err = 0;
315 break;
316
317 default:
318 err = tty_mode_ioctl(tty, file, cmd, arg);
319 break;
320 }
321
322 sp_put(ap);
323 return err;
324 }
325
326 /* No kernel lock - fine */
327 static __poll_t
ppp_sync_poll(struct tty_struct * tty,struct file * file,poll_table * wait)328 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
329 {
330 return 0;
331 }
332
333 /* May sleep, don't call from interrupt level or with interrupts disabled */
334 static void
ppp_sync_receive(struct tty_struct * tty,const unsigned char * buf,char * cflags,int count)335 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
336 char *cflags, int count)
337 {
338 struct syncppp *ap = sp_get(tty);
339 unsigned long flags;
340
341 if (!ap)
342 return;
343 spin_lock_irqsave(&ap->recv_lock, flags);
344 ppp_sync_input(ap, buf, cflags, count);
345 spin_unlock_irqrestore(&ap->recv_lock, flags);
346 if (!skb_queue_empty(&ap->rqueue))
347 tasklet_schedule(&ap->tsk);
348 sp_put(ap);
349 tty_unthrottle(tty);
350 }
351
352 static void
ppp_sync_wakeup(struct tty_struct * tty)353 ppp_sync_wakeup(struct tty_struct *tty)
354 {
355 struct syncppp *ap = sp_get(tty);
356
357 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
358 if (!ap)
359 return;
360 set_bit(XMIT_WAKEUP, &ap->xmit_flags);
361 tasklet_schedule(&ap->tsk);
362 sp_put(ap);
363 }
364
365
366 static struct tty_ldisc_ops ppp_sync_ldisc = {
367 .owner = THIS_MODULE,
368 .name = "pppsync",
369 .open = ppp_sync_open,
370 .close = ppp_sync_close,
371 .hangup = ppp_sync_hangup,
372 .read = ppp_sync_read,
373 .write = ppp_sync_write,
374 .ioctl = ppp_synctty_ioctl,
375 .poll = ppp_sync_poll,
376 .receive_buf = ppp_sync_receive,
377 .write_wakeup = ppp_sync_wakeup,
378 };
379
380 static int __init
ppp_sync_init(void)381 ppp_sync_init(void)
382 {
383 int err;
384
385 err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
386 if (err != 0)
387 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
388 err);
389 return err;
390 }
391
392 /*
393 * The following routines provide the PPP channel interface.
394 */
395 static int
ppp_sync_ioctl(struct ppp_channel * chan,unsigned int cmd,unsigned long arg)396 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
397 {
398 struct syncppp *ap = chan->private;
399 int err, val;
400 u32 accm[8];
401 void __user *argp = (void __user *)arg;
402 u32 __user *p = argp;
403
404 err = -EFAULT;
405 switch (cmd) {
406 case PPPIOCGFLAGS:
407 val = ap->flags | ap->rbits;
408 if (put_user(val, (int __user *) argp))
409 break;
410 err = 0;
411 break;
412 case PPPIOCSFLAGS:
413 if (get_user(val, (int __user *) argp))
414 break;
415 ap->flags = val & ~SC_RCV_BITS;
416 spin_lock_irq(&ap->recv_lock);
417 ap->rbits = val & SC_RCV_BITS;
418 spin_unlock_irq(&ap->recv_lock);
419 err = 0;
420 break;
421
422 case PPPIOCGASYNCMAP:
423 if (put_user(ap->xaccm[0], p))
424 break;
425 err = 0;
426 break;
427 case PPPIOCSASYNCMAP:
428 if (get_user(ap->xaccm[0], p))
429 break;
430 err = 0;
431 break;
432
433 case PPPIOCGRASYNCMAP:
434 if (put_user(ap->raccm, p))
435 break;
436 err = 0;
437 break;
438 case PPPIOCSRASYNCMAP:
439 if (get_user(ap->raccm, p))
440 break;
441 err = 0;
442 break;
443
444 case PPPIOCGXASYNCMAP:
445 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
446 break;
447 err = 0;
448 break;
449 case PPPIOCSXASYNCMAP:
450 if (copy_from_user(accm, argp, sizeof(accm)))
451 break;
452 accm[2] &= ~0x40000000U; /* can't escape 0x5e */
453 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
454 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
455 err = 0;
456 break;
457
458 case PPPIOCGMRU:
459 if (put_user(ap->mru, (int __user *) argp))
460 break;
461 err = 0;
462 break;
463 case PPPIOCSMRU:
464 if (get_user(val, (int __user *) argp))
465 break;
466 if (val < PPP_MRU)
467 val = PPP_MRU;
468 ap->mru = val;
469 err = 0;
470 break;
471
472 default:
473 err = -ENOTTY;
474 }
475 return err;
476 }
477
478 /*
479 * This is called at softirq level to deliver received packets
480 * to the ppp_generic code, and to tell the ppp_generic code
481 * if we can accept more output now.
482 */
ppp_sync_process(struct tasklet_struct * t)483 static void ppp_sync_process(struct tasklet_struct *t)
484 {
485 struct syncppp *ap = from_tasklet(ap, t, tsk);
486 struct sk_buff *skb;
487
488 /* process received packets */
489 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
490 if (skb->len == 0) {
491 /* zero length buffers indicate error */
492 ppp_input_error(&ap->chan, 0);
493 kfree_skb(skb);
494 }
495 else
496 ppp_input(&ap->chan, skb);
497 }
498
499 /* try to push more stuff out */
500 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
501 ppp_output_wakeup(&ap->chan);
502 }
503
504 /*
505 * Procedures for encapsulation and framing.
506 */
507
508 static struct sk_buff*
ppp_sync_txmunge(struct syncppp * ap,struct sk_buff * skb)509 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
510 {
511 int proto;
512 unsigned char *data;
513 int islcp;
514
515 data = skb->data;
516 proto = get_unaligned_be16(data);
517
518 /* LCP packets with codes between 1 (configure-request)
519 * and 7 (code-reject) must be sent as though no options
520 * have been negotiated.
521 */
522 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
523
524 /* compress protocol field if option enabled */
525 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
526 skb_pull(skb,1);
527
528 /* prepend address/control fields if necessary */
529 if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
530 if (skb_headroom(skb) < 2) {
531 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
532 if (npkt == NULL) {
533 kfree_skb(skb);
534 return NULL;
535 }
536 skb_reserve(npkt,2);
537 skb_copy_from_linear_data(skb,
538 skb_put(npkt, skb->len), skb->len);
539 consume_skb(skb);
540 skb = npkt;
541 }
542 skb_push(skb,2);
543 skb->data[0] = PPP_ALLSTATIONS;
544 skb->data[1] = PPP_UI;
545 }
546
547 ap->last_xmit = jiffies;
548
549 if (skb && ap->flags & SC_LOG_OUTPKT)
550 ppp_print_buffer ("send buffer", skb->data, skb->len);
551
552 return skb;
553 }
554
555 /*
556 * Transmit-side routines.
557 */
558
559 /*
560 * Send a packet to the peer over an sync tty line.
561 * Returns 1 iff the packet was accepted.
562 * If the packet was not accepted, we will call ppp_output_wakeup
563 * at some later time.
564 */
565 static int
ppp_sync_send(struct ppp_channel * chan,struct sk_buff * skb)566 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
567 {
568 struct syncppp *ap = chan->private;
569
570 ppp_sync_push(ap);
571
572 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
573 return 0; /* already full */
574 skb = ppp_sync_txmunge(ap, skb);
575 if (skb != NULL)
576 ap->tpkt = skb;
577 else
578 clear_bit(XMIT_FULL, &ap->xmit_flags);
579
580 ppp_sync_push(ap);
581 return 1;
582 }
583
584 /*
585 * Push as much data as possible out to the tty.
586 */
587 static int
ppp_sync_push(struct syncppp * ap)588 ppp_sync_push(struct syncppp *ap)
589 {
590 int sent, done = 0;
591 struct tty_struct *tty = ap->tty;
592 int tty_stuffed = 0;
593
594 if (!spin_trylock_bh(&ap->xmit_lock))
595 return 0;
596 for (;;) {
597 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
598 tty_stuffed = 0;
599 if (!tty_stuffed && ap->tpkt) {
600 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
601 sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
602 if (sent < 0)
603 goto flush; /* error, e.g. loss of CD */
604 if (sent < ap->tpkt->len) {
605 tty_stuffed = 1;
606 } else {
607 consume_skb(ap->tpkt);
608 ap->tpkt = NULL;
609 clear_bit(XMIT_FULL, &ap->xmit_flags);
610 done = 1;
611 }
612 continue;
613 }
614 /* haven't made any progress */
615 spin_unlock_bh(&ap->xmit_lock);
616 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
617 (!tty_stuffed && ap->tpkt)))
618 break;
619 if (!spin_trylock_bh(&ap->xmit_lock))
620 break;
621 }
622 return done;
623
624 flush:
625 if (ap->tpkt) {
626 kfree_skb(ap->tpkt);
627 ap->tpkt = NULL;
628 clear_bit(XMIT_FULL, &ap->xmit_flags);
629 done = 1;
630 }
631 spin_unlock_bh(&ap->xmit_lock);
632 return done;
633 }
634
635 /*
636 * Flush output from our internal buffers.
637 * Called for the TCFLSH ioctl.
638 */
639 static void
ppp_sync_flush_output(struct syncppp * ap)640 ppp_sync_flush_output(struct syncppp *ap)
641 {
642 int done = 0;
643
644 spin_lock_bh(&ap->xmit_lock);
645 if (ap->tpkt != NULL) {
646 kfree_skb(ap->tpkt);
647 ap->tpkt = NULL;
648 clear_bit(XMIT_FULL, &ap->xmit_flags);
649 done = 1;
650 }
651 spin_unlock_bh(&ap->xmit_lock);
652 if (done)
653 ppp_output_wakeup(&ap->chan);
654 }
655
656 /*
657 * Receive-side routines.
658 */
659
660 /* called when the tty driver has data for us.
661 *
662 * Data is frame oriented: each call to ppp_sync_input is considered
663 * a whole frame. If the 1st flag byte is non-zero then the whole
664 * frame is considered to be in error and is tossed.
665 */
666 static void
ppp_sync_input(struct syncppp * ap,const unsigned char * buf,char * flags,int count)667 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
668 char *flags, int count)
669 {
670 struct sk_buff *skb;
671 unsigned char *p;
672
673 if (count == 0)
674 return;
675
676 if (ap->flags & SC_LOG_INPKT)
677 ppp_print_buffer ("receive buffer", buf, count);
678
679 /* stuff the chars in the skb */
680 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
681 if (!skb) {
682 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
683 goto err;
684 }
685 /* Try to get the payload 4-byte aligned */
686 if (buf[0] != PPP_ALLSTATIONS)
687 skb_reserve(skb, 2 + (buf[0] & 1));
688
689 if (flags && *flags) {
690 /* error flag set, ignore frame */
691 goto err;
692 } else if (count > skb_tailroom(skb)) {
693 /* packet overflowed MRU */
694 goto err;
695 }
696
697 skb_put_data(skb, buf, count);
698
699 /* strip address/control field if present */
700 p = skb->data;
701 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
702 /* chop off address/control */
703 if (skb->len < 3)
704 goto err;
705 p = skb_pull(skb, 2);
706 }
707
708 /* PPP packet length should be >= 2 bytes when protocol field is not
709 * compressed.
710 */
711 if (!(p[0] & 0x01) && skb->len < 2)
712 goto err;
713
714 /* queue the frame to be processed */
715 skb_queue_tail(&ap->rqueue, skb);
716 return;
717
718 err:
719 /* queue zero length packet as error indication */
720 if (skb || (skb = dev_alloc_skb(0))) {
721 skb_trim(skb, 0);
722 skb_queue_tail(&ap->rqueue, skb);
723 }
724 }
725
726 static void __exit
ppp_sync_cleanup(void)727 ppp_sync_cleanup(void)
728 {
729 if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
730 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
731 }
732
733 module_init(ppp_sync_init);
734 module_exit(ppp_sync_cleanup);
735 MODULE_LICENSE("GPL");
736 MODULE_ALIAS_LDISC(N_SYNC_PPP);
737