blob: 4d51c0c8023d160b5d82c3d09e37e440fe0e16bf [file] [log] [blame]
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.
9 *
10 * 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;
111 static char hex[] = "0123456789ABCDEF";
112
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;
240
241 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
387static int
388ppp_sync_room(struct tty_struct *tty)
389{
390 return 65535;
391}
392
393/*
394 * This can now be called from hard interrupt level as well
395 * as soft interrupt level or mainline.
396 */
397static void
398ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
399 char *cflags, int count)
400{
401 struct syncppp *ap = sp_get(tty);
402 unsigned long flags;
403
404 if (ap == 0)
405 return;
406 spin_lock_irqsave(&ap->recv_lock, flags);
407 ppp_sync_input(ap, buf, cflags, count);
408 spin_unlock_irqrestore(&ap->recv_lock, flags);
David S. Millerb03efcf2005-07-08 14:57:23 -0700409 if (!skb_queue_empty(&ap->rqueue))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700410 tasklet_schedule(&ap->tsk);
411 sp_put(ap);
412 if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
413 && tty->driver->unthrottle)
414 tty->driver->unthrottle(tty);
415}
416
417static void
418ppp_sync_wakeup(struct tty_struct *tty)
419{
420 struct syncppp *ap = sp_get(tty);
421
422 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
423 if (ap == 0)
424 return;
425 set_bit(XMIT_WAKEUP, &ap->xmit_flags);
426 tasklet_schedule(&ap->tsk);
427 sp_put(ap);
428}
429
430
431static struct tty_ldisc ppp_sync_ldisc = {
432 .owner = THIS_MODULE,
433 .magic = TTY_LDISC_MAGIC,
434 .name = "pppsync",
435 .open = ppp_sync_open,
436 .close = ppp_sync_close,
437 .hangup = ppp_sync_hangup,
438 .read = ppp_sync_read,
439 .write = ppp_sync_write,
440 .ioctl = ppp_synctty_ioctl,
441 .poll = ppp_sync_poll,
442 .receive_room = ppp_sync_room,
443 .receive_buf = ppp_sync_receive,
444 .write_wakeup = ppp_sync_wakeup,
445};
446
447static int __init
448ppp_sync_init(void)
449{
450 int err;
451
452 err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
453 if (err != 0)
454 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
455 err);
456 return err;
457}
458
459/*
460 * The following routines provide the PPP channel interface.
461 */
462static int
463ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
464{
465 struct syncppp *ap = chan->private;
466 int err, val;
467 u32 accm[8];
468 void __user *argp = (void __user *)arg;
469 u32 __user *p = argp;
470
471 err = -EFAULT;
472 switch (cmd) {
473 case PPPIOCGFLAGS:
474 val = ap->flags | ap->rbits;
475 if (put_user(val, (int __user *) argp))
476 break;
477 err = 0;
478 break;
479 case PPPIOCSFLAGS:
480 if (get_user(val, (int __user *) argp))
481 break;
482 ap->flags = val & ~SC_RCV_BITS;
483 spin_lock_irq(&ap->recv_lock);
484 ap->rbits = val & SC_RCV_BITS;
485 spin_unlock_irq(&ap->recv_lock);
486 err = 0;
487 break;
488
489 case PPPIOCGASYNCMAP:
490 if (put_user(ap->xaccm[0], p))
491 break;
492 err = 0;
493 break;
494 case PPPIOCSASYNCMAP:
495 if (get_user(ap->xaccm[0], p))
496 break;
497 err = 0;
498 break;
499
500 case PPPIOCGRASYNCMAP:
501 if (put_user(ap->raccm, p))
502 break;
503 err = 0;
504 break;
505 case PPPIOCSRASYNCMAP:
506 if (get_user(ap->raccm, p))
507 break;
508 err = 0;
509 break;
510
511 case PPPIOCGXASYNCMAP:
512 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
513 break;
514 err = 0;
515 break;
516 case PPPIOCSXASYNCMAP:
517 if (copy_from_user(accm, argp, sizeof(accm)))
518 break;
519 accm[2] &= ~0x40000000U; /* can't escape 0x5e */
520 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
521 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
522 err = 0;
523 break;
524
525 case PPPIOCGMRU:
526 if (put_user(ap->mru, (int __user *) argp))
527 break;
528 err = 0;
529 break;
530 case PPPIOCSMRU:
531 if (get_user(val, (int __user *) argp))
532 break;
533 if (val < PPP_MRU)
534 val = PPP_MRU;
535 ap->mru = val;
536 err = 0;
537 break;
538
539 default:
540 err = -ENOTTY;
541 }
542 return err;
543}
544
545/*
546 * This is called at softirq level to deliver received packets
547 * to the ppp_generic code, and to tell the ppp_generic code
548 * if we can accept more output now.
549 */
550static void ppp_sync_process(unsigned long arg)
551{
552 struct syncppp *ap = (struct syncppp *) arg;
553 struct sk_buff *skb;
554
555 /* process received packets */
556 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
557 if (skb->len == 0) {
558 /* zero length buffers indicate error */
559 ppp_input_error(&ap->chan, 0);
560 kfree_skb(skb);
561 }
562 else
563 ppp_input(&ap->chan, skb);
564 }
565
566 /* try to push more stuff out */
567 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
568 ppp_output_wakeup(&ap->chan);
569}
570
571/*
572 * Procedures for encapsulation and framing.
573 */
574
575struct sk_buff*
576ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
577{
578 int proto;
579 unsigned char *data;
580 int islcp;
581
582 data = skb->data;
583 proto = (data[0] << 8) + data[1];
584
585 /* LCP packets with codes between 1 (configure-request)
586 * and 7 (code-reject) must be sent as though no options
587 * have been negotiated.
588 */
589 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
590
591 /* compress protocol field if option enabled */
592 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
593 skb_pull(skb,1);
594
595 /* prepend address/control fields if necessary */
596 if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
597 if (skb_headroom(skb) < 2) {
598 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
599 if (npkt == NULL) {
600 kfree_skb(skb);
601 return NULL;
602 }
603 skb_reserve(npkt,2);
604 memcpy(skb_put(npkt,skb->len), skb->data, skb->len);
605 kfree_skb(skb);
606 skb = npkt;
607 }
608 skb_push(skb,2);
609 skb->data[0] = PPP_ALLSTATIONS;
610 skb->data[1] = PPP_UI;
611 }
612
613 ap->last_xmit = jiffies;
614
615 if (skb && ap->flags & SC_LOG_OUTPKT)
616 ppp_print_buffer ("send buffer", skb->data, skb->len);
617
618 return skb;
619}
620
621/*
622 * Transmit-side routines.
623 */
624
625/*
626 * Send a packet to the peer over an sync tty line.
627 * Returns 1 iff the packet was accepted.
628 * If the packet was not accepted, we will call ppp_output_wakeup
629 * at some later time.
630 */
631static int
632ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
633{
634 struct syncppp *ap = chan->private;
635
636 ppp_sync_push(ap);
637
638 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
639 return 0; /* already full */
640 skb = ppp_sync_txmunge(ap, skb);
641 if (skb != NULL)
642 ap->tpkt = skb;
643 else
644 clear_bit(XMIT_FULL, &ap->xmit_flags);
645
646 ppp_sync_push(ap);
647 return 1;
648}
649
650/*
651 * Push as much data as possible out to the tty.
652 */
653static int
654ppp_sync_push(struct syncppp *ap)
655{
656 int sent, done = 0;
657 struct tty_struct *tty = ap->tty;
658 int tty_stuffed = 0;
659
660 if (!spin_trylock_bh(&ap->xmit_lock))
661 return 0;
662 for (;;) {
663 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
664 tty_stuffed = 0;
665 if (!tty_stuffed && ap->tpkt != 0) {
666 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
667 sent = tty->driver->write(tty, ap->tpkt->data, ap->tpkt->len);
668 if (sent < 0)
669 goto flush; /* error, e.g. loss of CD */
670 if (sent < ap->tpkt->len) {
671 tty_stuffed = 1;
672 } else {
673 kfree_skb(ap->tpkt);
674 ap->tpkt = NULL;
675 clear_bit(XMIT_FULL, &ap->xmit_flags);
676 done = 1;
677 }
678 continue;
679 }
680 /* haven't made any progress */
681 spin_unlock_bh(&ap->xmit_lock);
682 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
683 || (!tty_stuffed && ap->tpkt != 0)))
684 break;
685 if (!spin_trylock_bh(&ap->xmit_lock))
686 break;
687 }
688 return done;
689
690flush:
691 if (ap->tpkt != 0) {
692 kfree_skb(ap->tpkt);
693 ap->tpkt = NULL;
694 clear_bit(XMIT_FULL, &ap->xmit_flags);
695 done = 1;
696 }
697 spin_unlock_bh(&ap->xmit_lock);
698 return done;
699}
700
701/*
702 * Flush output from our internal buffers.
703 * Called for the TCFLSH ioctl.
704 */
705static void
706ppp_sync_flush_output(struct syncppp *ap)
707{
708 int done = 0;
709
710 spin_lock_bh(&ap->xmit_lock);
711 if (ap->tpkt != NULL) {
712 kfree_skb(ap->tpkt);
713 ap->tpkt = NULL;
714 clear_bit(XMIT_FULL, &ap->xmit_flags);
715 done = 1;
716 }
717 spin_unlock_bh(&ap->xmit_lock);
718 if (done)
719 ppp_output_wakeup(&ap->chan);
720}
721
722/*
723 * Receive-side routines.
724 */
725
726/* called when the tty driver has data for us.
727 *
728 * Data is frame oriented: each call to ppp_sync_input is considered
729 * a whole frame. If the 1st flag byte is non-zero then the whole
730 * frame is considered to be in error and is tossed.
731 */
732static void
733ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
734 char *flags, int count)
735{
736 struct sk_buff *skb;
737 unsigned char *p;
738
739 if (count == 0)
740 return;
741
742 if (ap->flags & SC_LOG_INPKT)
743 ppp_print_buffer ("receive buffer", buf, count);
744
745 /* stuff the chars in the skb */
746 if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
747 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
748 goto err;
749 }
750 /* Try to get the payload 4-byte aligned */
751 if (buf[0] != PPP_ALLSTATIONS)
752 skb_reserve(skb, 2 + (buf[0] & 1));
753
754 if (flags != 0 && *flags) {
755 /* error flag set, ignore frame */
756 goto err;
757 } else if (count > skb_tailroom(skb)) {
758 /* packet overflowed MRU */
759 goto err;
760 }
761
762 p = skb_put(skb, count);
763 memcpy(p, buf, count);
764
765 /* strip address/control field if present */
766 p = skb->data;
767 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
768 /* chop off address/control */
769 if (skb->len < 3)
770 goto err;
771 p = skb_pull(skb, 2);
772 }
773
774 /* decompress protocol field if compressed */
775 if (p[0] & 1) {
776 /* protocol is compressed */
777 skb_push(skb, 1)[0] = 0;
778 } else if (skb->len < 2)
779 goto err;
780
781 /* queue the frame to be processed */
782 skb_queue_tail(&ap->rqueue, skb);
783 return;
784
785err:
786 /* queue zero length packet as error indication */
787 if (skb || (skb = dev_alloc_skb(0))) {
788 skb_trim(skb, 0);
789 skb_queue_tail(&ap->rqueue, skb);
790 }
791}
792
793static void __exit
794ppp_sync_cleanup(void)
795{
Alexey Dobriyan64ccd712005-06-23 00:10:33 -0700796 if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700797 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
798}
799
800module_init(ppp_sync_init);
801module_exit(ppp_sync_cleanup);
802MODULE_LICENSE("GPL");
803MODULE_ALIAS_LDISC(N_SYNC_PPP);