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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * PPP synchronous tty channel driver for Linux.
3 *
4 * This is a ppp channel driver that can be used with tty device drivers
5 * that are frame oriented, such as synchronous HDLC devices.
6 *
7 * Complete PPP frames without encoding/decoding are exchanged between
8 * the channel driver and the device driver.
Jeff Garzik6aa20a22006-09-13 13:24:59 -04009 *
Linus Torvalds1da177e2005-04-16 15:20:36 -070010 * The async map IOCTL codes are implemented to keep the user mode
11 * applications happy if they call them. Synchronous PPP does not use
12 * the async maps.
13 *
14 * Copyright 1999 Paul Mackerras.
15 *
16 * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
17 *
18 * This program is free software; you can redistribute it and/or
19 * modify it under the terms of the GNU General Public License
20 * as published by the Free Software Foundation; either version
21 * 2 of the License, or (at your option) any later version.
22 *
23 * This driver provides the encapsulation and framing for sending
24 * and receiving PPP frames over sync serial lines. It relies on
25 * the generic PPP layer to give it frames to send and to process
26 * received frames. It implements the PPP line discipline.
27 *
28 * Part of the code in this driver was inspired by the old async-only
29 * PPP driver, written by Michael Callahan and Al Longyear, and
30 * subsequently hacked by Paul Mackerras.
31 *
32 * ==FILEVERSION 20040616==
33 */
34
35#include <linux/module.h>
36#include <linux/kernel.h>
37#include <linux/skbuff.h>
38#include <linux/tty.h>
39#include <linux/netdevice.h>
40#include <linux/poll.h>
41#include <linux/ppp_defs.h>
42#include <linux/if_ppp.h>
43#include <linux/ppp_channel.h>
44#include <linux/spinlock.h>
45#include <linux/init.h>
46#include <asm/uaccess.h>
47#include <asm/semaphore.h>
48
49#define PPP_VERSION "2.4.2"
50
51/* Structure for storing local state. */
52struct 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 atomic_t refcnt;
73 struct semaphore dead_sem;
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 */
89static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
90static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
91static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
92 unsigned long arg);
93static void ppp_sync_process(unsigned long arg);
94static int ppp_sync_push(struct syncppp *ap);
95static void ppp_sync_flush_output(struct syncppp *ap);
96static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
97 char *flags, int count);
98
99static struct ppp_channel_ops sync_ops = {
100 ppp_sync_send,
101 ppp_sync_ioctl
102};
103
104/*
105 * Utility procedures to print a buffer in hex/ascii
106 */
107static void
108ppp_print_hex (register __u8 * out, const __u8 * in, int count)
109{
110 register __u8 next_ch;
Arjan van de Venf71e1302006-03-03 21:33:57 -0500111 static const char hex[] = "0123456789ABCDEF";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700112
113 while (count-- > 0) {
114 next_ch = *in++;
115 *out++ = hex[(next_ch >> 4) & 0x0F];
116 *out++ = hex[next_ch & 0x0F];
117 ++out;
118 }
119}
120
121static void
122ppp_print_char (register __u8 * out, const __u8 * in, int count)
123{
124 register __u8 next_ch;
125
126 while (count-- > 0) {
127 next_ch = *in++;
128
129 if (next_ch < 0x20 || next_ch > 0x7e)
130 *out++ = '.';
131 else {
132 *out++ = next_ch;
133 if (next_ch == '%') /* printk/syslogd has a bug !! */
134 *out++ = '%';
135 }
136 }
137 *out = '\0';
138}
139
140static void
141ppp_print_buffer (const char *name, const __u8 *buf, int count)
142{
143 __u8 line[44];
144
145 if (name != NULL)
146 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
147
148 while (count > 8) {
149 memset (line, 32, 44);
150 ppp_print_hex (line, buf, 8);
151 ppp_print_char (&line[8 * 3], buf, 8);
152 printk(KERN_DEBUG "%s\n", line);
153 count -= 8;
154 buf += 8;
155 }
156
157 if (count > 0) {
158 memset (line, 32, 44);
159 ppp_print_hex (line, buf, count);
160 ppp_print_char (&line[8 * 3], buf, count);
161 printk(KERN_DEBUG "%s\n", line);
162 }
163}
164
165
166/*
167 * Routines implementing the synchronous PPP line discipline.
168 */
169
170/*
171 * We have a potential race on dereferencing tty->disc_data,
172 * because the tty layer provides no locking at all - thus one
173 * cpu could be running ppp_synctty_receive while another
174 * calls ppp_synctty_close, which zeroes tty->disc_data and
175 * frees the memory that ppp_synctty_receive is using. The best
176 * way to fix this is to use a rwlock in the tty struct, but for now
177 * we use a single global rwlock for all ttys in ppp line discipline.
178 *
179 * FIXME: Fixed in tty_io nowdays.
180 */
181static DEFINE_RWLOCK(disc_data_lock);
182
183static struct syncppp *sp_get(struct tty_struct *tty)
184{
185 struct syncppp *ap;
186
187 read_lock(&disc_data_lock);
188 ap = tty->disc_data;
189 if (ap != NULL)
190 atomic_inc(&ap->refcnt);
191 read_unlock(&disc_data_lock);
192 return ap;
193}
194
195static void sp_put(struct syncppp *ap)
196{
197 if (atomic_dec_and_test(&ap->refcnt))
198 up(&ap->dead_sem);
199}
200
201/*
202 * Called when a tty is put into sync-PPP line discipline.
203 */
204static int
205ppp_sync_open(struct tty_struct *tty)
206{
207 struct syncppp *ap;
208 int err;
209
210 ap = kmalloc(sizeof(*ap), GFP_KERNEL);
211 err = -ENOMEM;
212 if (ap == 0)
213 goto out;
214
215 /* initialize the syncppp structure */
216 memset(ap, 0, sizeof(*ap));
217 ap->tty = tty;
218 ap->mru = PPP_MRU;
219 spin_lock_init(&ap->xmit_lock);
220 spin_lock_init(&ap->recv_lock);
221 ap->xaccm[0] = ~0U;
222 ap->xaccm[3] = 0x60000000U;
223 ap->raccm = ~0U;
224
225 skb_queue_head_init(&ap->rqueue);
226 tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
227
228 atomic_set(&ap->refcnt, 1);
229 init_MUTEX_LOCKED(&ap->dead_sem);
230
231 ap->chan.private = ap;
232 ap->chan.ops = &sync_ops;
233 ap->chan.mtu = PPP_MRU;
234 ap->chan.hdrlen = 2; /* for A/C bytes */
235 err = ppp_register_channel(&ap->chan);
236 if (err)
237 goto out_free;
238
239 tty->disc_data = ap;
Alan Cox33f0f882006-01-09 20:54:13 -0800240 tty->receive_room = 65536;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241 return 0;
242
243 out_free:
244 kfree(ap);
245 out:
246 return err;
247}
248
249/*
250 * Called when the tty is put into another line discipline
251 * or it hangs up. We have to wait for any cpu currently
252 * executing in any of the other ppp_synctty_* routines to
253 * finish before we can call ppp_unregister_channel and free
254 * the syncppp struct. This routine must be called from
255 * process context, not interrupt or softirq context.
256 */
257static void
258ppp_sync_close(struct tty_struct *tty)
259{
260 struct syncppp *ap;
261
262 write_lock_irq(&disc_data_lock);
263 ap = tty->disc_data;
264 tty->disc_data = NULL;
265 write_unlock_irq(&disc_data_lock);
266 if (ap == 0)
267 return;
268
269 /*
270 * We have now ensured that nobody can start using ap from now
271 * on, but we have to wait for all existing users to finish.
272 * Note that ppp_unregister_channel ensures that no calls to
273 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
274 * by the time it returns.
275 */
276 if (!atomic_dec_and_test(&ap->refcnt))
277 down(&ap->dead_sem);
278 tasklet_kill(&ap->tsk);
279
280 ppp_unregister_channel(&ap->chan);
281 skb_queue_purge(&ap->rqueue);
282 if (ap->tpkt != 0)
283 kfree_skb(ap->tpkt);
284 kfree(ap);
285}
286
287/*
288 * Called on tty hangup in process context.
289 *
290 * Wait for I/O to driver to complete and unregister PPP channel.
291 * This is already done by the close routine, so just call that.
292 */
293static int ppp_sync_hangup(struct tty_struct *tty)
294{
295 ppp_sync_close(tty);
296 return 0;
297}
298
299/*
300 * Read does nothing - no data is ever available this way.
301 * Pppd reads and writes packets via /dev/ppp instead.
302 */
303static ssize_t
304ppp_sync_read(struct tty_struct *tty, struct file *file,
305 unsigned char __user *buf, size_t count)
306{
307 return -EAGAIN;
308}
309
310/*
311 * Write on the tty does nothing, the packets all come in
312 * from the ppp generic stuff.
313 */
314static ssize_t
315ppp_sync_write(struct tty_struct *tty, struct file *file,
316 const unsigned char *buf, size_t count)
317{
318 return -EAGAIN;
319}
320
321static int
322ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
323 unsigned int cmd, unsigned long arg)
324{
325 struct syncppp *ap = sp_get(tty);
326 int __user *p = (int __user *)arg;
327 int err, val;
328
329 if (ap == 0)
330 return -ENXIO;
331 err = -EFAULT;
332 switch (cmd) {
333 case PPPIOCGCHAN:
334 err = -ENXIO;
335 if (ap == 0)
336 break;
337 err = -EFAULT;
338 if (put_user(ppp_channel_index(&ap->chan), p))
339 break;
340 err = 0;
341 break;
342
343 case PPPIOCGUNIT:
344 err = -ENXIO;
345 if (ap == 0)
346 break;
347 err = -EFAULT;
348 if (put_user(ppp_unit_number(&ap->chan), p))
349 break;
350 err = 0;
351 break;
352
353 case TCGETS:
354 case TCGETA:
355 err = n_tty_ioctl(tty, file, cmd, arg);
356 break;
357
358 case TCFLSH:
359 /* flush our buffers and the serial port's buffer */
360 if (arg == TCIOFLUSH || arg == TCOFLUSH)
361 ppp_sync_flush_output(ap);
362 err = n_tty_ioctl(tty, file, cmd, arg);
363 break;
364
365 case FIONREAD:
366 val = 0;
367 if (put_user(val, p))
368 break;
369 err = 0;
370 break;
371
372 default:
373 err = -ENOIOCTLCMD;
374 }
375
376 sp_put(ap);
377 return err;
378}
379
380/* No kernel lock - fine */
381static unsigned int
382ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
383{
384 return 0;
385}
386
Linus Torvalds1da177e2005-04-16 15:20:36 -0700387/*
388 * This can now be called from hard interrupt level as well
389 * as soft interrupt level or mainline.
390 */
391static void
392ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
393 char *cflags, int count)
394{
395 struct syncppp *ap = sp_get(tty);
396 unsigned long flags;
397
398 if (ap == 0)
399 return;
400 spin_lock_irqsave(&ap->recv_lock, flags);
401 ppp_sync_input(ap, buf, cflags, count);
402 spin_unlock_irqrestore(&ap->recv_lock, flags);
David S. Millerb03efcf2005-07-08 14:57:23 -0700403 if (!skb_queue_empty(&ap->rqueue))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700404 tasklet_schedule(&ap->tsk);
405 sp_put(ap);
406 if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
407 && tty->driver->unthrottle)
408 tty->driver->unthrottle(tty);
409}
410
411static void
412ppp_sync_wakeup(struct tty_struct *tty)
413{
414 struct syncppp *ap = sp_get(tty);
415
416 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
417 if (ap == 0)
418 return;
419 set_bit(XMIT_WAKEUP, &ap->xmit_flags);
420 tasklet_schedule(&ap->tsk);
421 sp_put(ap);
422}
423
424
425static struct tty_ldisc ppp_sync_ldisc = {
426 .owner = THIS_MODULE,
427 .magic = TTY_LDISC_MAGIC,
428 .name = "pppsync",
429 .open = ppp_sync_open,
430 .close = ppp_sync_close,
431 .hangup = ppp_sync_hangup,
432 .read = ppp_sync_read,
433 .write = ppp_sync_write,
434 .ioctl = ppp_synctty_ioctl,
435 .poll = ppp_sync_poll,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700436 .receive_buf = ppp_sync_receive,
437 .write_wakeup = ppp_sync_wakeup,
438};
439
440static int __init
441ppp_sync_init(void)
442{
443 int err;
444
445 err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
446 if (err != 0)
447 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
448 err);
449 return err;
450}
451
452/*
453 * The following routines provide the PPP channel interface.
454 */
455static int
456ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
457{
458 struct syncppp *ap = chan->private;
459 int err, val;
460 u32 accm[8];
461 void __user *argp = (void __user *)arg;
462 u32 __user *p = argp;
463
464 err = -EFAULT;
465 switch (cmd) {
466 case PPPIOCGFLAGS:
467 val = ap->flags | ap->rbits;
468 if (put_user(val, (int __user *) argp))
469 break;
470 err = 0;
471 break;
472 case PPPIOCSFLAGS:
473 if (get_user(val, (int __user *) argp))
474 break;
475 ap->flags = val & ~SC_RCV_BITS;
476 spin_lock_irq(&ap->recv_lock);
477 ap->rbits = val & SC_RCV_BITS;
478 spin_unlock_irq(&ap->recv_lock);
479 err = 0;
480 break;
481
482 case PPPIOCGASYNCMAP:
483 if (put_user(ap->xaccm[0], p))
484 break;
485 err = 0;
486 break;
487 case PPPIOCSASYNCMAP:
488 if (get_user(ap->xaccm[0], p))
489 break;
490 err = 0;
491 break;
492
493 case PPPIOCGRASYNCMAP:
494 if (put_user(ap->raccm, p))
495 break;
496 err = 0;
497 break;
498 case PPPIOCSRASYNCMAP:
499 if (get_user(ap->raccm, p))
500 break;
501 err = 0;
502 break;
503
504 case PPPIOCGXASYNCMAP:
505 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
506 break;
507 err = 0;
508 break;
509 case PPPIOCSXASYNCMAP:
510 if (copy_from_user(accm, argp, sizeof(accm)))
511 break;
512 accm[2] &= ~0x40000000U; /* can't escape 0x5e */
513 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
514 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
515 err = 0;
516 break;
517
518 case PPPIOCGMRU:
519 if (put_user(ap->mru, (int __user *) argp))
520 break;
521 err = 0;
522 break;
523 case PPPIOCSMRU:
524 if (get_user(val, (int __user *) argp))
525 break;
526 if (val < PPP_MRU)
527 val = PPP_MRU;
528 ap->mru = val;
529 err = 0;
530 break;
531
532 default:
533 err = -ENOTTY;
534 }
535 return err;
536}
537
538/*
539 * This is called at softirq level to deliver received packets
540 * to the ppp_generic code, and to tell the ppp_generic code
541 * if we can accept more output now.
542 */
543static void ppp_sync_process(unsigned long arg)
544{
545 struct syncppp *ap = (struct syncppp *) arg;
546 struct sk_buff *skb;
547
548 /* process received packets */
549 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
550 if (skb->len == 0) {
551 /* zero length buffers indicate error */
552 ppp_input_error(&ap->chan, 0);
553 kfree_skb(skb);
554 }
555 else
556 ppp_input(&ap->chan, skb);
557 }
558
559 /* try to push more stuff out */
560 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
561 ppp_output_wakeup(&ap->chan);
562}
563
564/*
565 * Procedures for encapsulation and framing.
566 */
567
568struct sk_buff*
569ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
570{
571 int proto;
572 unsigned char *data;
573 int islcp;
574
575 data = skb->data;
576 proto = (data[0] << 8) + data[1];
577
578 /* LCP packets with codes between 1 (configure-request)
579 * and 7 (code-reject) must be sent as though no options
580 * have been negotiated.
581 */
582 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
583
584 /* compress protocol field if option enabled */
585 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
586 skb_pull(skb,1);
587
588 /* prepend address/control fields if necessary */
589 if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
590 if (skb_headroom(skb) < 2) {
591 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
592 if (npkt == NULL) {
593 kfree_skb(skb);
594 return NULL;
595 }
596 skb_reserve(npkt,2);
Arnaldo Carvalho de Melod626f622007-03-27 18:55:52 -0300597 skb_copy_from_linear_data(skb,
598 skb_put(npkt, skb->len), skb->len);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700599 kfree_skb(skb);
600 skb = npkt;
601 }
602 skb_push(skb,2);
603 skb->data[0] = PPP_ALLSTATIONS;
604 skb->data[1] = PPP_UI;
605 }
606
607 ap->last_xmit = jiffies;
608
609 if (skb && ap->flags & SC_LOG_OUTPKT)
610 ppp_print_buffer ("send buffer", skb->data, skb->len);
611
612 return skb;
613}
614
615/*
616 * Transmit-side routines.
617 */
618
619/*
620 * Send a packet to the peer over an sync tty line.
621 * Returns 1 iff the packet was accepted.
622 * If the packet was not accepted, we will call ppp_output_wakeup
623 * at some later time.
624 */
625static int
626ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
627{
628 struct syncppp *ap = chan->private;
629
630 ppp_sync_push(ap);
631
632 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
633 return 0; /* already full */
634 skb = ppp_sync_txmunge(ap, skb);
635 if (skb != NULL)
636 ap->tpkt = skb;
637 else
638 clear_bit(XMIT_FULL, &ap->xmit_flags);
639
640 ppp_sync_push(ap);
641 return 1;
642}
643
644/*
645 * Push as much data as possible out to the tty.
646 */
647static int
648ppp_sync_push(struct syncppp *ap)
649{
650 int sent, done = 0;
651 struct tty_struct *tty = ap->tty;
652 int tty_stuffed = 0;
653
654 if (!spin_trylock_bh(&ap->xmit_lock))
655 return 0;
656 for (;;) {
657 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
658 tty_stuffed = 0;
659 if (!tty_stuffed && ap->tpkt != 0) {
660 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
661 sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
662 if (sent < 0)
663 goto flush; /* error, e.g. loss of CD */
664 if (sent < ap->tpkt->len) {
665 tty_stuffed = 1;
666 } else {
667 kfree_skb(ap->tpkt);
668 ap->tpkt = NULL;
669 clear_bit(XMIT_FULL, &ap->xmit_flags);
670 done = 1;
671 }
672 continue;
673 }
674 /* haven't made any progress */
675 spin_unlock_bh(&ap->xmit_lock);
676 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
677 || (!tty_stuffed && ap->tpkt != 0)))
678 break;
679 if (!spin_trylock_bh(&ap->xmit_lock))
680 break;
681 }
682 return done;
683
684flush:
685 if (ap->tpkt != 0) {
686 kfree_skb(ap->tpkt);
687 ap->tpkt = NULL;
688 clear_bit(XMIT_FULL, &ap->xmit_flags);
689 done = 1;
690 }
691 spin_unlock_bh(&ap->xmit_lock);
692 return done;
693}
694
695/*
696 * Flush output from our internal buffers.
697 * Called for the TCFLSH ioctl.
698 */
699static void
700ppp_sync_flush_output(struct syncppp *ap)
701{
702 int done = 0;
703
704 spin_lock_bh(&ap->xmit_lock);
705 if (ap->tpkt != NULL) {
706 kfree_skb(ap->tpkt);
707 ap->tpkt = NULL;
708 clear_bit(XMIT_FULL, &ap->xmit_flags);
709 done = 1;
710 }
711 spin_unlock_bh(&ap->xmit_lock);
712 if (done)
713 ppp_output_wakeup(&ap->chan);
714}
715
716/*
717 * Receive-side routines.
718 */
719
720/* called when the tty driver has data for us.
721 *
722 * Data is frame oriented: each call to ppp_sync_input is considered
723 * a whole frame. If the 1st flag byte is non-zero then the whole
724 * frame is considered to be in error and is tossed.
725 */
726static void
727ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
728 char *flags, int count)
729{
730 struct sk_buff *skb;
731 unsigned char *p;
732
733 if (count == 0)
734 return;
735
736 if (ap->flags & SC_LOG_INPKT)
737 ppp_print_buffer ("receive buffer", buf, count);
738
739 /* stuff the chars in the skb */
740 if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
741 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
742 goto err;
743 }
744 /* Try to get the payload 4-byte aligned */
745 if (buf[0] != PPP_ALLSTATIONS)
746 skb_reserve(skb, 2 + (buf[0] & 1));
747
748 if (flags != 0 && *flags) {
749 /* error flag set, ignore frame */
750 goto err;
751 } else if (count > skb_tailroom(skb)) {
752 /* packet overflowed MRU */
753 goto err;
754 }
755
756 p = skb_put(skb, count);
757 memcpy(p, buf, count);
758
759 /* strip address/control field if present */
760 p = skb->data;
761 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
762 /* chop off address/control */
763 if (skb->len < 3)
764 goto err;
765 p = skb_pull(skb, 2);
766 }
767
768 /* decompress protocol field if compressed */
769 if (p[0] & 1) {
770 /* protocol is compressed */
771 skb_push(skb, 1)[0] = 0;
772 } else if (skb->len < 2)
773 goto err;
774
775 /* queue the frame to be processed */
776 skb_queue_tail(&ap->rqueue, skb);
777 return;
778
779err:
780 /* queue zero length packet as error indication */
781 if (skb || (skb = dev_alloc_skb(0))) {
782 skb_trim(skb, 0);
783 skb_queue_tail(&ap->rqueue, skb);
784 }
785}
786
787static void __exit
788ppp_sync_cleanup(void)
789{
Alexey Dobriyan64ccd712005-06-23 00:10:33 -0700790 if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700791 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
792}
793
794module_init(ppp_sync_init);
795module_exit(ppp_sync_cleanup);
796MODULE_LICENSE("GPL");
797MODULE_ALIAS_LDISC(N_SYNC_PPP);