xref: /linux/drivers/net/slip/slip.c (revision 621cde16e49b3ecf7d59a8106a20aaebfb4a59a9)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * slip.c	This module implements the SLIP protocol for kernel-based
4  *		devices like TTY.  It interfaces between a raw TTY, and the
5  *		kernel's INET protocol layers.
6  *
7  * Version:	@(#)slip.c	0.8.3	12/24/94
8  *
9  * Authors:	Laurence Culhane, <loz@holmes.demon.co.uk>
10  *		Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
11  *
12  * Fixes:
13  *		Alan Cox	: 	Sanity checks and avoid tx overruns.
14  *					Has a new sl->mtu field.
15  *		Alan Cox	: 	Found cause of overrun. ifconfig sl0
16  *					mtu upwards. Driver now spots this
17  *					and grows/shrinks its buffers(hack!).
18  *					Memory leak if you run out of memory
19  *					setting up a slip driver fixed.
20  *		Matt Dillon	:	Printable slip (borrowed from NET2E)
21  *	Pauline Middelink	:	Slip driver fixes.
22  *		Alan Cox	:	Honours the old SL_COMPRESSED flag
23  *		Alan Cox	:	KISS AX.25 and AXUI IP support
24  *		Michael Riepe	:	Automatic CSLIP recognition added
25  *		Charles Hedrick :	CSLIP header length problem fix.
26  *		Alan Cox	:	Corrected non-IP cases of the above.
27  *		Alan Cox	:	Now uses hardware type as per FvK.
28  *		Alan Cox	:	Default to 192.168.0.0 (RFC 1597)
29  *		A.N.Kuznetsov	:	dev_tint() recursion fix.
30  *	Dmitry Gorodchanin	:	SLIP memory leaks
31  *      Dmitry Gorodchanin      :       Code cleanup. Reduce tty driver
32  *                                      buffering from 4096 to 256 bytes.
33  *                                      Improving SLIP response time.
34  *                                      CONFIG_SLIP_MODE_SLIP6.
35  *                                      ifconfig sl? up & down now works
36  *					correctly.
37  *					Modularization.
38  *              Alan Cox        :       Oops - fix AX.25 buffer lengths
39  *      Dmitry Gorodchanin      :       Even more cleanups. Preserve CSLIP
40  *                                      statistics. Include CSLIP code only
41  *                                      if it really needed.
42  *		Alan Cox	:	Free slhc buffers in the right place.
43  *		Alan Cox	:	Allow for digipeated IP over AX.25
44  *		Matti Aarnio	:	Dynamic SLIP devices, with ideas taken
45  *					from Jim Freeman's <jfree@caldera.com>
46  *					dynamic PPP devices.  We do NOT kfree()
47  *					device entries, just reg./unreg. them
48  *					as they are needed.  We kfree() them
49  *					at module cleanup.
50  *					With MODULE-loading ``insmod'', user
51  *					can issue parameter:  slip_maxdev=1024
52  *					(Or how much he/she wants.. Default
53  *					is 256)
54  *	Stanislav Voronyi	:	Slip line checking, with ideas taken
55  *					from multislip BSDI driver which was
56  *					written by Igor Chechik, RELCOM Corp.
57  *					Only algorithms have been ported to
58  *					Linux SLIP driver.
59  *	Vitaly E. Lavrov	:	Sane behaviour on tty hangup.
60  *	Alexey Kuznetsov	:	Cleanup interfaces to tty & netdevice
61  *					modules.
62  */
63 
64 #define SL_CHECK_TRANSMIT
65 #include <linux/compat.h>
66 #include <linux/module.h>
67 #include <linux/moduleparam.h>
68 
69 #include <linux/uaccess.h>
70 #include <linux/bitops.h>
71 #include <linux/sched/signal.h>
72 #include <linux/string.h>
73 #include <linux/mm.h>
74 #include <linux/interrupt.h>
75 #include <linux/in.h>
76 #include <linux/tty.h>
77 #include <linux/errno.h>
78 #include <linux/netdevice.h>
79 #include <linux/etherdevice.h>
80 #include <linux/skbuff.h>
81 #include <linux/rtnetlink.h>
82 #include <linux/if_arp.h>
83 #include <linux/if_slip.h>
84 #include <linux/delay.h>
85 #include <linux/init.h>
86 #include <linux/slab.h>
87 #include <linux/workqueue.h>
88 #include "slip.h"
89 #ifdef CONFIG_INET
90 #include <linux/ip.h>
91 #include <linux/tcp.h>
92 #include <net/slhc_vj.h>
93 #endif
94 
95 #define SLIP_VERSION	"0.8.4-NET3.019-NEWTTY"
96 
97 static struct net_device **slip_devs;
98 
99 static int slip_maxdev = SL_NRUNIT;
100 module_param(slip_maxdev, int, 0);
101 MODULE_PARM_DESC(slip_maxdev, "Maximum number of slip devices");
102 
103 static int slip_esc(unsigned char *p, unsigned char *d, int len);
104 static void slip_unesc(struct slip *sl, unsigned char c);
105 #ifdef CONFIG_SLIP_MODE_SLIP6
106 static int slip_esc6(unsigned char *p, unsigned char *d, int len);
107 static void slip_unesc6(struct slip *sl, unsigned char c);
108 #endif
109 #ifdef CONFIG_SLIP_SMART
110 static void sl_keepalive(struct timer_list *t);
111 static void sl_outfill(struct timer_list *t);
112 static int sl_siocdevprivate(struct net_device *dev, struct ifreq *rq, void __user *data, int cmd);
113 #endif
114 
115 /********************************
116 *  Buffer administration routines:
117 *	sl_alloc_bufs()
118 *	sl_free_bufs()
119 *	sl_realloc_bufs()
120 *
121 * NOTE: sl_realloc_bufs != sl_free_bufs + sl_alloc_bufs, because
122 *	sl_realloc_bufs provides strong atomicity and reallocation
123 *	on actively running device.
124 *********************************/
125 
126 /*
127    Allocate channel buffers.
128  */
129 
sl_alloc_bufs(struct slip * sl,int mtu)130 static int sl_alloc_bufs(struct slip *sl, int mtu)
131 {
132 	int err = -ENOBUFS;
133 	unsigned long len;
134 	char *rbuff = NULL;
135 	char *xbuff = NULL;
136 #ifdef SL_INCLUDE_CSLIP
137 	char *cbuff = NULL;
138 	struct slcompress *slcomp = NULL;
139 #endif
140 
141 	/*
142 	 * Allocate the SLIP frame buffers:
143 	 *
144 	 * rbuff	Receive buffer.
145 	 * xbuff	Transmit buffer.
146 	 * cbuff        Temporary compression buffer.
147 	 */
148 	len = mtu * 2;
149 
150 	/*
151 	 * allow for arrival of larger UDP packets, even if we say not to
152 	 * also fixes a bug in which SunOS sends 512-byte packets even with
153 	 * an MSS of 128
154 	 */
155 	if (len < 576 * 2)
156 		len = 576 * 2;
157 	rbuff = kmalloc(len + 4, GFP_KERNEL);
158 	if (rbuff == NULL)
159 		goto err_exit;
160 	xbuff = kmalloc(len + 4, GFP_KERNEL);
161 	if (xbuff == NULL)
162 		goto err_exit;
163 #ifdef SL_INCLUDE_CSLIP
164 	cbuff = kmalloc(len + 4, GFP_KERNEL);
165 	if (cbuff == NULL)
166 		goto err_exit;
167 	slcomp = slhc_init(16, 16);
168 	if (IS_ERR(slcomp))
169 		goto err_exit;
170 #endif
171 	spin_lock_bh(&sl->lock);
172 	if (sl->tty == NULL) {
173 		spin_unlock_bh(&sl->lock);
174 		err = -ENODEV;
175 		goto err_exit;
176 	}
177 	sl->mtu	     = mtu;
178 	sl->buffsize = len;
179 	sl->rcount   = 0;
180 	sl->xleft    = 0;
181 	rbuff = xchg(&sl->rbuff, rbuff);
182 	xbuff = xchg(&sl->xbuff, xbuff);
183 #ifdef SL_INCLUDE_CSLIP
184 	cbuff = xchg(&sl->cbuff, cbuff);
185 	slcomp = xchg(&sl->slcomp, slcomp);
186 #endif
187 #ifdef CONFIG_SLIP_MODE_SLIP6
188 	sl->xdata    = 0;
189 	sl->xbits    = 0;
190 #endif
191 	spin_unlock_bh(&sl->lock);
192 	err = 0;
193 
194 	/* Cleanup */
195 err_exit:
196 #ifdef SL_INCLUDE_CSLIP
197 	kfree(cbuff);
198 	slhc_free(slcomp);
199 #endif
200 	kfree(xbuff);
201 	kfree(rbuff);
202 	return err;
203 }
204 
205 /* Free a SLIP channel buffers. */
sl_free_bufs(struct slip * sl)206 static void sl_free_bufs(struct slip *sl)
207 {
208 	/* Free all SLIP frame buffers. */
209 	kfree(xchg(&sl->rbuff, NULL));
210 	kfree(xchg(&sl->xbuff, NULL));
211 #ifdef SL_INCLUDE_CSLIP
212 	kfree(xchg(&sl->cbuff, NULL));
213 	slhc_free(xchg(&sl->slcomp, NULL));
214 #endif
215 }
216 
217 /*
218    Reallocate slip channel buffers.
219  */
220 
sl_realloc_bufs(struct slip * sl,int mtu)221 static int sl_realloc_bufs(struct slip *sl, int mtu)
222 {
223 	int err = 0;
224 	struct net_device *dev = sl->dev;
225 	unsigned char *xbuff, *rbuff;
226 #ifdef SL_INCLUDE_CSLIP
227 	unsigned char *cbuff;
228 #endif
229 	int len = mtu * 2;
230 
231 /*
232  * allow for arrival of larger UDP packets, even if we say not to
233  * also fixes a bug in which SunOS sends 512-byte packets even with
234  * an MSS of 128
235  */
236 	if (len < 576 * 2)
237 		len = 576 * 2;
238 
239 	xbuff = kmalloc(len + 4, GFP_ATOMIC);
240 	rbuff = kmalloc(len + 4, GFP_ATOMIC);
241 #ifdef SL_INCLUDE_CSLIP
242 	cbuff = kmalloc(len + 4, GFP_ATOMIC);
243 #endif
244 
245 
246 #ifdef SL_INCLUDE_CSLIP
247 	if (xbuff == NULL || rbuff == NULL || cbuff == NULL)  {
248 #else
249 	if (xbuff == NULL || rbuff == NULL)  {
250 #endif
251 		if (mtu > sl->mtu) {
252 			printk(KERN_WARNING "%s: unable to grow slip buffers, MTU change cancelled.\n",
253 			       dev->name);
254 			err = -ENOBUFS;
255 		}
256 		goto done;
257 	}
258 	spin_lock_bh(&sl->lock);
259 
260 	err = -ENODEV;
261 	if (sl->tty == NULL)
262 		goto done_on_bh;
263 
264 	xbuff    = xchg(&sl->xbuff, xbuff);
265 	rbuff    = xchg(&sl->rbuff, rbuff);
266 #ifdef SL_INCLUDE_CSLIP
267 	cbuff    = xchg(&sl->cbuff, cbuff);
268 #endif
269 	if (sl->xleft)  {
270 		if (sl->xleft <= len)  {
271 			memcpy(sl->xbuff, sl->xhead, sl->xleft);
272 		} else  {
273 			sl->xleft = 0;
274 			dev->stats.tx_dropped++;
275 		}
276 	}
277 	sl->xhead = sl->xbuff;
278 
279 	if (sl->rcount)  {
280 		if (sl->rcount <= len) {
281 			memcpy(sl->rbuff, rbuff, sl->rcount);
282 		} else  {
283 			sl->rcount = 0;
284 			dev->stats.rx_over_errors++;
285 			set_bit(SLF_ERROR, &sl->flags);
286 		}
287 	}
288 	sl->mtu      = mtu;
289 	WRITE_ONCE(dev->mtu, mtu);
290 	sl->buffsize = len;
291 	err = 0;
292 
293 done_on_bh:
294 	spin_unlock_bh(&sl->lock);
295 
296 done:
297 	kfree(xbuff);
298 	kfree(rbuff);
299 #ifdef SL_INCLUDE_CSLIP
300 	kfree(cbuff);
301 #endif
302 	return err;
303 }
304 
305 
306 /* Set the "sending" flag.  This must be atomic hence the set_bit. */
307 static inline void sl_lock(struct slip *sl)
308 {
309 	netif_stop_queue(sl->dev);
310 }
311 
312 
313 /* Clear the "sending" flag.  This must be atomic, hence the ASM. */
314 static inline void sl_unlock(struct slip *sl)
315 {
316 	netif_wake_queue(sl->dev);
317 }
318 
319 /* Send one completely decapsulated IP datagram to the IP layer. */
320 static void sl_bump(struct slip *sl)
321 {
322 	struct net_device *dev = sl->dev;
323 	struct sk_buff *skb;
324 	int count;
325 
326 	count = sl->rcount;
327 #ifdef SL_INCLUDE_CSLIP
328 	if (sl->mode & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) {
329 		unsigned char c = sl->rbuff[0];
330 		if (c & SL_TYPE_COMPRESSED_TCP) {
331 			/* ignore compressed packets when CSLIP is off */
332 			if (!(sl->mode & SL_MODE_CSLIP)) {
333 				printk(KERN_WARNING "%s: compressed packet ignored\n", dev->name);
334 				return;
335 			}
336 			/* make sure we've reserved enough space for uncompress
337 			   to use */
338 			if (count + 80 > sl->buffsize) {
339 				dev->stats.rx_over_errors++;
340 				return;
341 			}
342 			count = slhc_uncompress(sl->slcomp, sl->rbuff, count);
343 			if (count <= 0)
344 				return;
345 		} else if (c >= SL_TYPE_UNCOMPRESSED_TCP) {
346 			if (!(sl->mode & SL_MODE_CSLIP)) {
347 				/* turn on header compression */
348 				sl->mode |= SL_MODE_CSLIP;
349 				sl->mode &= ~SL_MODE_ADAPTIVE;
350 				printk(KERN_INFO "%s: header compression turned on\n", dev->name);
351 			}
352 			sl->rbuff[0] &= 0x4f;
353 			if (slhc_remember(sl->slcomp, sl->rbuff, count) <= 0)
354 				return;
355 		}
356 	}
357 #endif  /* SL_INCLUDE_CSLIP */
358 
359 	dev->stats.rx_bytes += count;
360 
361 	skb = dev_alloc_skb(count);
362 	if (skb == NULL) {
363 		printk(KERN_WARNING "%s: memory squeeze, dropping packet.\n", dev->name);
364 		dev->stats.rx_dropped++;
365 		return;
366 	}
367 	skb->dev = dev;
368 	skb_put_data(skb, sl->rbuff, count);
369 	skb_reset_mac_header(skb);
370 	skb->protocol = htons(ETH_P_IP);
371 	netif_rx(skb);
372 	dev->stats.rx_packets++;
373 }
374 
375 /* Encapsulate one IP datagram and stuff into a TTY queue. */
376 static void sl_encaps(struct slip *sl, unsigned char *icp, int len)
377 {
378 	unsigned char *p;
379 	int actual, count;
380 
381 	if (len > sl->mtu) {		/* Sigh, shouldn't occur BUT ... */
382 		printk(KERN_WARNING "%s: truncating oversized transmit packet!\n", sl->dev->name);
383 		sl->dev->stats.tx_dropped++;
384 		sl_unlock(sl);
385 		return;
386 	}
387 
388 	p = icp;
389 #ifdef SL_INCLUDE_CSLIP
390 	if (sl->mode & SL_MODE_CSLIP)
391 		len = slhc_compress(sl->slcomp, p, len, sl->cbuff, &p, 1);
392 #endif
393 #ifdef CONFIG_SLIP_MODE_SLIP6
394 	if (sl->mode & SL_MODE_SLIP6)
395 		count = slip_esc6(p, sl->xbuff, len);
396 	else
397 #endif
398 		count = slip_esc(p, sl->xbuff, len);
399 
400 	/* Order of next two lines is *very* important.
401 	 * When we are sending a little amount of data,
402 	 * the transfer may be completed inside the ops->write()
403 	 * routine, because it's running with interrupts enabled.
404 	 * In this case we *never* got WRITE_WAKEUP event,
405 	 * if we did not request it before write operation.
406 	 *       14 Oct 1994  Dmitry Gorodchanin.
407 	 */
408 	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
409 	actual = sl->tty->ops->write(sl->tty, sl->xbuff, count);
410 #ifdef SL_CHECK_TRANSMIT
411 	netif_trans_update(sl->dev);
412 #endif
413 	sl->xleft = count - actual;
414 	sl->xhead = sl->xbuff + actual;
415 #ifdef CONFIG_SLIP_SMART
416 	/* VSV */
417 	clear_bit(SLF_OUTWAIT, &sl->flags);	/* reset outfill flag */
418 #endif
419 }
420 
421 /* Write out any remaining transmit buffer. Scheduled when tty is writable */
422 static void slip_transmit(struct work_struct *work)
423 {
424 	struct slip *sl = container_of(work, struct slip, tx_work);
425 	int actual;
426 
427 	spin_lock_bh(&sl->lock);
428 	/* First make sure we're connected. */
429 	if (!sl->tty || sl->magic != SLIP_MAGIC || !netif_running(sl->dev)) {
430 		spin_unlock_bh(&sl->lock);
431 		return;
432 	}
433 
434 	if (sl->xleft <= 0)  {
435 		/* Now serial buffer is almost free & we can start
436 		 * transmission of another packet */
437 		sl->dev->stats.tx_packets++;
438 		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
439 		spin_unlock_bh(&sl->lock);
440 		sl_unlock(sl);
441 		return;
442 	}
443 
444 	actual = sl->tty->ops->write(sl->tty, sl->xhead, sl->xleft);
445 	sl->xleft -= actual;
446 	sl->xhead += actual;
447 	spin_unlock_bh(&sl->lock);
448 }
449 
450 /*
451  * Called by the driver when there's room for more data.
452  * Schedule the transmit.
453  */
454 static void slip_write_wakeup(struct tty_struct *tty)
455 {
456 	struct slip *sl;
457 
458 	rcu_read_lock();
459 	sl = rcu_dereference(tty->disc_data);
460 	if (sl)
461 		schedule_work(&sl->tx_work);
462 	rcu_read_unlock();
463 }
464 
465 static void sl_tx_timeout(struct net_device *dev, unsigned int txqueue)
466 {
467 	struct slip *sl = netdev_priv(dev);
468 
469 	spin_lock(&sl->lock);
470 
471 	if (netif_queue_stopped(dev)) {
472 		if (!netif_running(dev) || !sl->tty)
473 			goto out;
474 
475 		/* May be we must check transmitter timeout here ?
476 		 *      14 Oct 1994 Dmitry Gorodchanin.
477 		 */
478 #ifdef SL_CHECK_TRANSMIT
479 		if (time_before(jiffies, dev_trans_start(dev) + 20 * HZ))  {
480 			/* 20 sec timeout not reached */
481 			goto out;
482 		}
483 		printk(KERN_WARNING "%s: transmit timed out, %s?\n",
484 			dev->name,
485 			(tty_chars_in_buffer(sl->tty) || sl->xleft) ?
486 				"bad line quality" : "driver error");
487 		sl->xleft = 0;
488 		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
489 		sl_unlock(sl);
490 #endif
491 	}
492 out:
493 	spin_unlock(&sl->lock);
494 }
495 
496 
497 /* Encapsulate an IP datagram and kick it into a TTY queue. */
498 static netdev_tx_t
499 sl_xmit(struct sk_buff *skb, struct net_device *dev)
500 {
501 	struct slip *sl = netdev_priv(dev);
502 
503 	spin_lock(&sl->lock);
504 	if (!netif_running(dev)) {
505 		spin_unlock(&sl->lock);
506 		printk(KERN_WARNING "%s: xmit call when iface is down\n", dev->name);
507 		dev_kfree_skb(skb);
508 		return NETDEV_TX_OK;
509 	}
510 	if (sl->tty == NULL) {
511 		spin_unlock(&sl->lock);
512 		dev_kfree_skb(skb);
513 		return NETDEV_TX_OK;
514 	}
515 
516 	sl_lock(sl);
517 	dev->stats.tx_bytes += skb->len;
518 	sl_encaps(sl, skb->data, skb->len);
519 	spin_unlock(&sl->lock);
520 
521 	dev_kfree_skb(skb);
522 	return NETDEV_TX_OK;
523 }
524 
525 
526 /******************************************
527  *   Routines looking at netdevice side.
528  ******************************************/
529 
530 /* Netdevice UP -> DOWN routine */
531 
532 static int
533 sl_close(struct net_device *dev)
534 {
535 	struct slip *sl = netdev_priv(dev);
536 
537 	spin_lock_bh(&sl->lock);
538 	if (sl->tty)
539 		/* TTY discipline is running. */
540 		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
541 	netif_stop_queue(dev);
542 	sl->rcount   = 0;
543 	sl->xleft    = 0;
544 	spin_unlock_bh(&sl->lock);
545 
546 	return 0;
547 }
548 
549 /* Netdevice DOWN -> UP routine */
550 
551 static int sl_open(struct net_device *dev)
552 {
553 	struct slip *sl = netdev_priv(dev);
554 
555 	if (sl->tty == NULL)
556 		return -ENODEV;
557 
558 	sl->flags &= (1 << SLF_INUSE);
559 	netif_start_queue(dev);
560 	return 0;
561 }
562 
563 /* Netdevice change MTU request */
564 
565 static int sl_change_mtu(struct net_device *dev, int new_mtu)
566 {
567 	struct slip *sl = netdev_priv(dev);
568 
569 	return sl_realloc_bufs(sl, new_mtu);
570 }
571 
572 /* Netdevice get statistics request */
573 
574 static void
575 sl_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
576 {
577 	struct net_device_stats *devstats = &dev->stats;
578 #ifdef SL_INCLUDE_CSLIP
579 	struct slip *sl = netdev_priv(dev);
580 	struct slcompress *comp = sl->slcomp;
581 #endif
582 	stats->rx_packets     = devstats->rx_packets;
583 	stats->tx_packets     = devstats->tx_packets;
584 	stats->rx_bytes       = devstats->rx_bytes;
585 	stats->tx_bytes       = devstats->tx_bytes;
586 	stats->rx_dropped     = devstats->rx_dropped;
587 	stats->tx_dropped     = devstats->tx_dropped;
588 	stats->tx_errors      = devstats->tx_errors;
589 	stats->rx_errors      = devstats->rx_errors;
590 	stats->rx_over_errors = devstats->rx_over_errors;
591 
592 #ifdef SL_INCLUDE_CSLIP
593 	if (comp) {
594 		/* Generic compressed statistics */
595 		stats->rx_compressed   = comp->sls_i_compressed;
596 		stats->tx_compressed   = comp->sls_o_compressed;
597 
598 		/* Are we really still needs this? */
599 		stats->rx_fifo_errors += comp->sls_i_compressed;
600 		stats->rx_dropped     += comp->sls_i_tossed;
601 		stats->tx_fifo_errors += comp->sls_o_compressed;
602 		stats->collisions     += comp->sls_o_misses;
603 	}
604 #endif
605 }
606 
607 /* Netdevice register callback */
608 
609 static int sl_init(struct net_device *dev)
610 {
611 	struct slip *sl = netdev_priv(dev);
612 
613 	/*
614 	 *	Finish setting up the DEVICE info.
615 	 */
616 
617 	dev->mtu		= sl->mtu;
618 	dev->type		= ARPHRD_SLIP + sl->mode;
619 #ifdef SL_CHECK_TRANSMIT
620 	dev->watchdog_timeo	= 20*HZ;
621 #endif
622 	return 0;
623 }
624 
625 
626 static void sl_uninit(struct net_device *dev)
627 {
628 	struct slip *sl = netdev_priv(dev);
629 
630 	sl_free_bufs(sl);
631 }
632 
633 /* Hook the destructor so we can free slip devices at the right point in time */
634 static void sl_free_netdev(struct net_device *dev)
635 {
636 	int i = dev->base_addr;
637 
638 	slip_devs[i] = NULL;
639 }
640 
641 static const struct net_device_ops sl_netdev_ops = {
642 	.ndo_init		= sl_init,
643 	.ndo_uninit	  	= sl_uninit,
644 	.ndo_open		= sl_open,
645 	.ndo_stop		= sl_close,
646 	.ndo_start_xmit		= sl_xmit,
647 	.ndo_get_stats64        = sl_get_stats64,
648 	.ndo_change_mtu		= sl_change_mtu,
649 	.ndo_tx_timeout		= sl_tx_timeout,
650 #ifdef CONFIG_SLIP_SMART
651 	.ndo_siocdevprivate	= sl_siocdevprivate,
652 #endif
653 };
654 
655 
656 static void sl_setup(struct net_device *dev)
657 {
658 	dev->netdev_ops		= &sl_netdev_ops;
659 	dev->needs_free_netdev	= true;
660 	dev->priv_destructor	= sl_free_netdev;
661 
662 	dev->hard_header_len	= 0;
663 	dev->addr_len		= 0;
664 	dev->tx_queue_len	= 10;
665 
666 	/* MTU range: 68 - 65534 */
667 	dev->min_mtu = 68;
668 	dev->max_mtu = 65534;
669 
670 	/* New-style flags. */
671 	dev->flags		= IFF_NOARP|IFF_POINTOPOINT|IFF_MULTICAST;
672 }
673 
674 /******************************************
675   Routines looking at TTY side.
676  ******************************************/
677 
678 
679 /*
680  * Handle the 'receiver data ready' interrupt.
681  * This function is called by the 'tty_io' module in the kernel when
682  * a block of SLIP data has been received, which can now be decapsulated
683  * and sent on to some IP layer for further processing. This will not
684  * be re-entered while running but other ldisc functions may be called
685  * in parallel
686  */
687 
688 static void slip_receive_buf(struct tty_struct *tty, const u8 *cp, const u8 *fp,
689 			     size_t count)
690 {
691 	struct slip *sl = tty->disc_data;
692 
693 	if (!sl || sl->magic != SLIP_MAGIC || !netif_running(sl->dev))
694 		return;
695 
696 	/* Read the characters out of the buffer */
697 	while (count--) {
698 		if (fp && *fp++) {
699 			if (!test_and_set_bit(SLF_ERROR, &sl->flags))
700 				sl->dev->stats.rx_errors++;
701 			cp++;
702 			continue;
703 		}
704 #ifdef CONFIG_SLIP_MODE_SLIP6
705 		if (sl->mode & SL_MODE_SLIP6)
706 			slip_unesc6(sl, *cp++);
707 		else
708 #endif
709 			slip_unesc(sl, *cp++);
710 	}
711 }
712 
713 /************************************
714  *  slip_open helper routines.
715  ************************************/
716 
717 /* Collect hanged up channels */
718 static void sl_sync(void)
719 {
720 	int i;
721 	struct net_device *dev;
722 	struct slip	  *sl;
723 
724 	for (i = 0; i < slip_maxdev; i++) {
725 		dev = slip_devs[i];
726 		if (dev == NULL)
727 			break;
728 
729 		sl = netdev_priv(dev);
730 		if (sl->tty || sl->leased)
731 			continue;
732 		if (dev->flags & IFF_UP)
733 			dev_close(dev);
734 	}
735 }
736 
737 
738 /* Find a free SLIP channel, and link in this `tty' line. */
739 static struct slip *sl_alloc(void)
740 {
741 	int i;
742 	char name[IFNAMSIZ];
743 	struct net_device *dev = NULL;
744 	struct slip       *sl;
745 
746 	for (i = 0; i < slip_maxdev; i++) {
747 		dev = slip_devs[i];
748 		if (dev == NULL)
749 			break;
750 	}
751 	/* Sorry, too many, all slots in use */
752 	if (i >= slip_maxdev)
753 		return NULL;
754 
755 	sprintf(name, "sl%d", i);
756 	dev = alloc_netdev(sizeof(*sl), name, NET_NAME_UNKNOWN, sl_setup);
757 	if (!dev)
758 		return NULL;
759 
760 	dev->base_addr  = i;
761 	sl = netdev_priv(dev);
762 
763 	/* Initialize channel control data */
764 	sl->magic       = SLIP_MAGIC;
765 	sl->dev	      	= dev;
766 	spin_lock_init(&sl->lock);
767 	INIT_WORK(&sl->tx_work, slip_transmit);
768 	sl->mode        = SL_MODE_DEFAULT;
769 #ifdef CONFIG_SLIP_SMART
770 	/* initialize timer_list struct */
771 	timer_setup(&sl->keepalive_timer, sl_keepalive, 0);
772 	timer_setup(&sl->outfill_timer, sl_outfill, 0);
773 #endif
774 	slip_devs[i] = dev;
775 	return sl;
776 }
777 
778 /*
779  * Open the high-level part of the SLIP channel.
780  * This function is called by the TTY module when the
781  * SLIP line discipline is called for.  Because we are
782  * sure the tty line exists, we only have to link it to
783  * a free SLIP channel...
784  *
785  * Called in process context serialized from other ldisc calls.
786  */
787 
788 static int slip_open(struct tty_struct *tty)
789 {
790 	struct slip *sl;
791 	int err;
792 
793 	if (!capable(CAP_NET_ADMIN))
794 		return -EPERM;
795 
796 	if (tty->ops->write == NULL)
797 		return -EOPNOTSUPP;
798 
799 	/* RTnetlink lock is misused here to serialize concurrent
800 	   opens of slip channels. There are better ways, but it is
801 	   the simplest one.
802 	 */
803 	rtnl_lock();
804 
805 	/* Collect hanged up channels. */
806 	sl_sync();
807 
808 	sl = tty->disc_data;
809 
810 	err = -EEXIST;
811 	/* First make sure we're not already connected. */
812 	if (sl && sl->magic == SLIP_MAGIC)
813 		goto err_exit;
814 
815 	/* OK.  Find a free SLIP channel to use. */
816 	err = -ENFILE;
817 	sl = sl_alloc();
818 	if (sl == NULL)
819 		goto err_exit;
820 
821 	sl->tty = tty;
822 	tty->disc_data = sl;
823 	sl->pid = current->pid;
824 
825 	if (!test_bit(SLF_INUSE, &sl->flags)) {
826 		/* Perform the low-level SLIP initialization. */
827 		err = sl_alloc_bufs(sl, SL_MTU);
828 		if (err)
829 			goto err_free_chan;
830 
831 		set_bit(SLF_INUSE, &sl->flags);
832 
833 		err = register_netdevice(sl->dev);
834 		if (err)
835 			goto err_free_bufs;
836 	}
837 
838 #ifdef CONFIG_SLIP_SMART
839 	if (sl->keepalive) {
840 		sl->keepalive_timer.expires = jiffies + sl->keepalive * HZ;
841 		add_timer(&sl->keepalive_timer);
842 	}
843 	if (sl->outfill) {
844 		sl->outfill_timer.expires = jiffies + sl->outfill * HZ;
845 		add_timer(&sl->outfill_timer);
846 	}
847 #endif
848 
849 	/* Done.  We have linked the TTY line to a channel. */
850 	rtnl_unlock();
851 	tty->receive_room = 65536;	/* We don't flow control */
852 
853 	/* TTY layer expects 0 on success */
854 	return 0;
855 
856 err_free_bufs:
857 	sl_free_bufs(sl);
858 
859 err_free_chan:
860 	sl->tty = NULL;
861 	tty->disc_data = NULL;
862 	clear_bit(SLF_INUSE, &sl->flags);
863 	sl_free_netdev(sl->dev);
864 	/* do not call free_netdev before rtnl_unlock */
865 	rtnl_unlock();
866 	free_netdev(sl->dev);
867 	return err;
868 
869 err_exit:
870 	rtnl_unlock();
871 
872 	/* Count references from TTY module */
873 	return err;
874 }
875 
876 /*
877  * Close down a SLIP channel.
878  * This means flushing out any pending queues, and then returning. This
879  * call is serialized against other ldisc functions.
880  *
881  * We also use this method fo a hangup event
882  */
883 
884 static void slip_close(struct tty_struct *tty)
885 {
886 	struct slip *sl = tty->disc_data;
887 
888 	/* First make sure we're connected. */
889 	if (!sl || sl->magic != SLIP_MAGIC || sl->tty != tty)
890 		return;
891 
892 	spin_lock_bh(&sl->lock);
893 	rcu_assign_pointer(tty->disc_data, NULL);
894 	sl->tty = NULL;
895 	spin_unlock_bh(&sl->lock);
896 
897 	synchronize_rcu();
898 	flush_work(&sl->tx_work);
899 
900 	/* VSV = very important to remove timers */
901 #ifdef CONFIG_SLIP_SMART
902 	del_timer_sync(&sl->keepalive_timer);
903 	del_timer_sync(&sl->outfill_timer);
904 #endif
905 	/* Flush network side */
906 	unregister_netdev(sl->dev);
907 	/* This will complete via sl_free_netdev */
908 }
909 
910 static void slip_hangup(struct tty_struct *tty)
911 {
912 	slip_close(tty);
913 }
914  /************************************************************************
915   *			STANDARD SLIP ENCAPSULATION		  	 *
916   ************************************************************************/
917 
918 static int slip_esc(unsigned char *s, unsigned char *d, int len)
919 {
920 	unsigned char *ptr = d;
921 	unsigned char c;
922 
923 	/*
924 	 * Send an initial END character to flush out any
925 	 * data that may have accumulated in the receiver
926 	 * due to line noise.
927 	 */
928 
929 	*ptr++ = END;
930 
931 	/*
932 	 * For each byte in the packet, send the appropriate
933 	 * character sequence, according to the SLIP protocol.
934 	 */
935 
936 	while (len-- > 0) {
937 		switch (c = *s++) {
938 		case END:
939 			*ptr++ = ESC;
940 			*ptr++ = ESC_END;
941 			break;
942 		case ESC:
943 			*ptr++ = ESC;
944 			*ptr++ = ESC_ESC;
945 			break;
946 		default:
947 			*ptr++ = c;
948 			break;
949 		}
950 	}
951 	*ptr++ = END;
952 	return ptr - d;
953 }
954 
955 static void slip_unesc(struct slip *sl, unsigned char s)
956 {
957 
958 	switch (s) {
959 	case END:
960 #ifdef CONFIG_SLIP_SMART
961 		/* drop keeptest bit = VSV */
962 		if (test_bit(SLF_KEEPTEST, &sl->flags))
963 			clear_bit(SLF_KEEPTEST, &sl->flags);
964 #endif
965 
966 		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
967 		    (sl->rcount > 2))
968 			sl_bump(sl);
969 		clear_bit(SLF_ESCAPE, &sl->flags);
970 		sl->rcount = 0;
971 		return;
972 
973 	case ESC:
974 		set_bit(SLF_ESCAPE, &sl->flags);
975 		return;
976 	case ESC_ESC:
977 		if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
978 			s = ESC;
979 		break;
980 	case ESC_END:
981 		if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
982 			s = END;
983 		break;
984 	}
985 	if (!test_bit(SLF_ERROR, &sl->flags))  {
986 		if (sl->rcount < sl->buffsize)  {
987 			sl->rbuff[sl->rcount++] = s;
988 			return;
989 		}
990 		sl->dev->stats.rx_over_errors++;
991 		set_bit(SLF_ERROR, &sl->flags);
992 	}
993 }
994 
995 
996 #ifdef CONFIG_SLIP_MODE_SLIP6
997 /************************************************************************
998  *			 6 BIT SLIP ENCAPSULATION			*
999  ************************************************************************/
1000 
1001 static int slip_esc6(unsigned char *s, unsigned char *d, int len)
1002 {
1003 	unsigned char *ptr = d;
1004 	unsigned char c;
1005 	int i;
1006 	unsigned short v = 0;
1007 	short bits = 0;
1008 
1009 	/*
1010 	 * Send an initial END character to flush out any
1011 	 * data that may have accumulated in the receiver
1012 	 * due to line noise.
1013 	 */
1014 
1015 	*ptr++ = 0x70;
1016 
1017 	/*
1018 	 * Encode the packet into printable ascii characters
1019 	 */
1020 
1021 	for (i = 0; i < len; ++i) {
1022 		v = (v << 8) | s[i];
1023 		bits += 8;
1024 		while (bits >= 6) {
1025 			bits -= 6;
1026 			c = 0x30 + ((v >> bits) & 0x3F);
1027 			*ptr++ = c;
1028 		}
1029 	}
1030 	if (bits) {
1031 		c = 0x30 + ((v << (6 - bits)) & 0x3F);
1032 		*ptr++ = c;
1033 	}
1034 	*ptr++ = 0x70;
1035 	return ptr - d;
1036 }
1037 
1038 static void slip_unesc6(struct slip *sl, unsigned char s)
1039 {
1040 	unsigned char c;
1041 
1042 	if (s == 0x70) {
1043 #ifdef CONFIG_SLIP_SMART
1044 		/* drop keeptest bit = VSV */
1045 		if (test_bit(SLF_KEEPTEST, &sl->flags))
1046 			clear_bit(SLF_KEEPTEST, &sl->flags);
1047 #endif
1048 
1049 		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
1050 		    (sl->rcount > 2))
1051 			sl_bump(sl);
1052 		sl->rcount = 0;
1053 		sl->xbits = 0;
1054 		sl->xdata = 0;
1055 	} else if (s >= 0x30 && s < 0x70) {
1056 		sl->xdata = (sl->xdata << 6) | ((s - 0x30) & 0x3F);
1057 		sl->xbits += 6;
1058 		if (sl->xbits >= 8) {
1059 			sl->xbits -= 8;
1060 			c = (unsigned char)(sl->xdata >> sl->xbits);
1061 			if (!test_bit(SLF_ERROR, &sl->flags))  {
1062 				if (sl->rcount < sl->buffsize)  {
1063 					sl->rbuff[sl->rcount++] = c;
1064 					return;
1065 				}
1066 				sl->dev->stats.rx_over_errors++;
1067 				set_bit(SLF_ERROR, &sl->flags);
1068 			}
1069 		}
1070 	}
1071 }
1072 #endif /* CONFIG_SLIP_MODE_SLIP6 */
1073 
1074 /* Perform I/O control on an active SLIP channel. */
1075 static int slip_ioctl(struct tty_struct *tty, unsigned int cmd,
1076 		unsigned long arg)
1077 {
1078 	struct slip *sl = tty->disc_data;
1079 	unsigned int tmp;
1080 	int __user *p = (int __user *)arg;
1081 
1082 	/* First make sure we're connected. */
1083 	if (!sl || sl->magic != SLIP_MAGIC)
1084 		return -EINVAL;
1085 
1086 	switch (cmd) {
1087 	case SIOCGIFNAME:
1088 		tmp = strlen(sl->dev->name) + 1;
1089 		if (copy_to_user((void __user *)arg, sl->dev->name, tmp))
1090 			return -EFAULT;
1091 		return 0;
1092 
1093 	case SIOCGIFENCAP:
1094 		if (put_user(sl->mode, p))
1095 			return -EFAULT;
1096 		return 0;
1097 
1098 	case SIOCSIFENCAP:
1099 		if (get_user(tmp, p))
1100 			return -EFAULT;
1101 #ifndef SL_INCLUDE_CSLIP
1102 		if (tmp & (SL_MODE_CSLIP|SL_MODE_ADAPTIVE))
1103 			return -EINVAL;
1104 #else
1105 		if ((tmp & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) ==
1106 		    (SL_MODE_ADAPTIVE | SL_MODE_CSLIP))
1107 			/* return -EINVAL; */
1108 			tmp &= ~SL_MODE_ADAPTIVE;
1109 #endif
1110 #ifndef CONFIG_SLIP_MODE_SLIP6
1111 		if (tmp & SL_MODE_SLIP6)
1112 			return -EINVAL;
1113 #endif
1114 		sl->mode = tmp;
1115 		sl->dev->type = ARPHRD_SLIP + sl->mode;
1116 		return 0;
1117 
1118 	case SIOCSIFHWADDR:
1119 		return -EINVAL;
1120 
1121 #ifdef CONFIG_SLIP_SMART
1122 	/* VSV changes start here */
1123 	case SIOCSKEEPALIVE:
1124 		if (get_user(tmp, p))
1125 			return -EFAULT;
1126 		if (tmp > 255) /* max for unchar */
1127 			return -EINVAL;
1128 
1129 		spin_lock_bh(&sl->lock);
1130 		if (!sl->tty) {
1131 			spin_unlock_bh(&sl->lock);
1132 			return -ENODEV;
1133 		}
1134 		sl->keepalive = (u8)tmp;
1135 		if (sl->keepalive != 0) {
1136 			mod_timer(&sl->keepalive_timer,
1137 					jiffies + sl->keepalive * HZ);
1138 			set_bit(SLF_KEEPTEST, &sl->flags);
1139 		} else
1140 			del_timer(&sl->keepalive_timer);
1141 		spin_unlock_bh(&sl->lock);
1142 		return 0;
1143 
1144 	case SIOCGKEEPALIVE:
1145 		if (put_user(sl->keepalive, p))
1146 			return -EFAULT;
1147 		return 0;
1148 
1149 	case SIOCSOUTFILL:
1150 		if (get_user(tmp, p))
1151 			return -EFAULT;
1152 		if (tmp > 255) /* max for unchar */
1153 			return -EINVAL;
1154 		spin_lock_bh(&sl->lock);
1155 		if (!sl->tty) {
1156 			spin_unlock_bh(&sl->lock);
1157 			return -ENODEV;
1158 		}
1159 		sl->outfill = (u8)tmp;
1160 		if (sl->outfill != 0) {
1161 			mod_timer(&sl->outfill_timer,
1162 						jiffies + sl->outfill * HZ);
1163 			set_bit(SLF_OUTWAIT, &sl->flags);
1164 		} else
1165 			del_timer(&sl->outfill_timer);
1166 		spin_unlock_bh(&sl->lock);
1167 		return 0;
1168 
1169 	case SIOCGOUTFILL:
1170 		if (put_user(sl->outfill, p))
1171 			return -EFAULT;
1172 		return 0;
1173 	/* VSV changes end */
1174 #endif
1175 	default:
1176 		return tty_mode_ioctl(tty, cmd, arg);
1177 	}
1178 }
1179 
1180 /* VSV changes start here */
1181 #ifdef CONFIG_SLIP_SMART
1182 /* function sl_siocdevprivate called from net/core/dev.c
1183    to allow get/set outfill/keepalive parameter
1184    by ifconfig                                 */
1185 
1186 static int sl_siocdevprivate(struct net_device *dev, struct ifreq *rq,
1187 			     void __user *data, int cmd)
1188 {
1189 	struct slip *sl = netdev_priv(dev);
1190 	unsigned long *p = (unsigned long *)&rq->ifr_ifru;
1191 
1192 	if (sl == NULL)		/* Allocation failed ?? */
1193 		return -ENODEV;
1194 
1195 	if (in_compat_syscall())
1196 		return -EOPNOTSUPP;
1197 
1198 	spin_lock_bh(&sl->lock);
1199 
1200 	if (!sl->tty) {
1201 		spin_unlock_bh(&sl->lock);
1202 		return -ENODEV;
1203 	}
1204 
1205 	switch (cmd) {
1206 	case SIOCSKEEPALIVE:
1207 		/* max for unchar */
1208 		if ((unsigned)*p > 255) {
1209 			spin_unlock_bh(&sl->lock);
1210 			return -EINVAL;
1211 		}
1212 		sl->keepalive = (u8)*p;
1213 		if (sl->keepalive != 0) {
1214 			sl->keepalive_timer.expires =
1215 						jiffies + sl->keepalive * HZ;
1216 			mod_timer(&sl->keepalive_timer,
1217 						jiffies + sl->keepalive * HZ);
1218 			set_bit(SLF_KEEPTEST, &sl->flags);
1219 		} else
1220 			del_timer(&sl->keepalive_timer);
1221 		break;
1222 
1223 	case SIOCGKEEPALIVE:
1224 		*p = sl->keepalive;
1225 		break;
1226 
1227 	case SIOCSOUTFILL:
1228 		if ((unsigned)*p > 255) { /* max for unchar */
1229 			spin_unlock_bh(&sl->lock);
1230 			return -EINVAL;
1231 		}
1232 		sl->outfill = (u8)*p;
1233 		if (sl->outfill != 0) {
1234 			mod_timer(&sl->outfill_timer,
1235 						jiffies + sl->outfill * HZ);
1236 			set_bit(SLF_OUTWAIT, &sl->flags);
1237 		} else
1238 			del_timer(&sl->outfill_timer);
1239 		break;
1240 
1241 	case SIOCGOUTFILL:
1242 		*p = sl->outfill;
1243 		break;
1244 
1245 	case SIOCSLEASE:
1246 		/* Resolve race condition, when ioctl'ing hanged up
1247 		   and opened by another process device.
1248 		 */
1249 		if (sl->tty != current->signal->tty &&
1250 						sl->pid != current->pid) {
1251 			spin_unlock_bh(&sl->lock);
1252 			return -EPERM;
1253 		}
1254 		sl->leased = 0;
1255 		if (*p)
1256 			sl->leased = 1;
1257 		break;
1258 
1259 	case SIOCGLEASE:
1260 		*p = sl->leased;
1261 	}
1262 	spin_unlock_bh(&sl->lock);
1263 	return 0;
1264 }
1265 #endif
1266 /* VSV changes end */
1267 
1268 static struct tty_ldisc_ops sl_ldisc = {
1269 	.owner 		= THIS_MODULE,
1270 	.num		= N_SLIP,
1271 	.name 		= "slip",
1272 	.open 		= slip_open,
1273 	.close	 	= slip_close,
1274 	.hangup	 	= slip_hangup,
1275 	.ioctl		= slip_ioctl,
1276 	.receive_buf	= slip_receive_buf,
1277 	.write_wakeup	= slip_write_wakeup,
1278 };
1279 
1280 static int __init slip_init(void)
1281 {
1282 	int status;
1283 
1284 	if (slip_maxdev < 4)
1285 		slip_maxdev = 4; /* Sanity */
1286 
1287 	printk(KERN_INFO "SLIP: version %s (dynamic channels, max=%d)"
1288 #ifdef CONFIG_SLIP_MODE_SLIP6
1289 	       " (6 bit encapsulation enabled)"
1290 #endif
1291 	       ".\n",
1292 	       SLIP_VERSION, slip_maxdev);
1293 #if defined(SL_INCLUDE_CSLIP)
1294 	printk(KERN_INFO "CSLIP: code copyright 1989 Regents of the University of California.\n");
1295 #endif
1296 #ifdef CONFIG_SLIP_SMART
1297 	printk(KERN_INFO "SLIP linefill/keepalive option.\n");
1298 #endif
1299 
1300 	slip_devs = kcalloc(slip_maxdev, sizeof(struct net_device *),
1301 								GFP_KERNEL);
1302 	if (!slip_devs)
1303 		return -ENOMEM;
1304 
1305 	/* Fill in our line protocol discipline, and register it */
1306 	status = tty_register_ldisc(&sl_ldisc);
1307 	if (status != 0) {
1308 		printk(KERN_ERR "SLIP: can't register line discipline (err = %d)\n", status);
1309 		kfree(slip_devs);
1310 	}
1311 	return status;
1312 }
1313 
1314 static void __exit slip_exit(void)
1315 {
1316 	int i;
1317 	struct net_device *dev;
1318 	struct slip *sl;
1319 	unsigned long timeout = jiffies + HZ;
1320 	int busy = 0;
1321 
1322 	if (slip_devs == NULL)
1323 		return;
1324 
1325 	/* First of all: check for active disciplines and hangup them.
1326 	 */
1327 	do {
1328 		if (busy)
1329 			msleep_interruptible(100);
1330 
1331 		busy = 0;
1332 		for (i = 0; i < slip_maxdev; i++) {
1333 			dev = slip_devs[i];
1334 			if (!dev)
1335 				continue;
1336 			sl = netdev_priv(dev);
1337 			spin_lock_bh(&sl->lock);
1338 			if (sl->tty) {
1339 				busy++;
1340 				tty_hangup(sl->tty);
1341 			}
1342 			spin_unlock_bh(&sl->lock);
1343 		}
1344 	} while (busy && time_before(jiffies, timeout));
1345 
1346 	/* FIXME: hangup is async so we should wait when doing this second
1347 	   phase */
1348 
1349 	for (i = 0; i < slip_maxdev; i++) {
1350 		dev = slip_devs[i];
1351 		if (!dev)
1352 			continue;
1353 		slip_devs[i] = NULL;
1354 
1355 		sl = netdev_priv(dev);
1356 		if (sl->tty) {
1357 			printk(KERN_ERR "%s: tty discipline still running\n",
1358 			       dev->name);
1359 		}
1360 
1361 		unregister_netdev(dev);
1362 	}
1363 
1364 	kfree(slip_devs);
1365 	slip_devs = NULL;
1366 
1367 	tty_unregister_ldisc(&sl_ldisc);
1368 }
1369 
1370 module_init(slip_init);
1371 module_exit(slip_exit);
1372 
1373 #ifdef CONFIG_SLIP_SMART
1374 /*
1375  * This is start of the code for multislip style line checking
1376  * added by Stanislav Voronyi. All changes before marked VSV
1377  */
1378 
1379 static void sl_outfill(struct timer_list *t)
1380 {
1381 	struct slip *sl = from_timer(sl, t, outfill_timer);
1382 
1383 	spin_lock(&sl->lock);
1384 
1385 	if (sl->tty == NULL)
1386 		goto out;
1387 
1388 	if (sl->outfill) {
1389 		if (test_bit(SLF_OUTWAIT, &sl->flags)) {
1390 			/* no packets were transmitted, do outfill */
1391 #ifdef CONFIG_SLIP_MODE_SLIP6
1392 			unsigned char s = (sl->mode & SL_MODE_SLIP6)?0x70:END;
1393 #else
1394 			unsigned char s = END;
1395 #endif
1396 			/* put END into tty queue. Is it right ??? */
1397 			if (!netif_queue_stopped(sl->dev)) {
1398 				/* if device busy no outfill */
1399 				sl->tty->ops->write(sl->tty, &s, 1);
1400 			}
1401 		} else
1402 			set_bit(SLF_OUTWAIT, &sl->flags);
1403 
1404 		mod_timer(&sl->outfill_timer, jiffies+sl->outfill*HZ);
1405 	}
1406 out:
1407 	spin_unlock(&sl->lock);
1408 }
1409 
1410 static void sl_keepalive(struct timer_list *t)
1411 {
1412 	struct slip *sl = from_timer(sl, t, keepalive_timer);
1413 
1414 	spin_lock(&sl->lock);
1415 
1416 	if (sl->tty == NULL)
1417 		goto out;
1418 
1419 	if (sl->keepalive) {
1420 		if (test_bit(SLF_KEEPTEST, &sl->flags)) {
1421 			/* keepalive still high :(, we must hangup */
1422 			if (sl->outfill)
1423 				/* outfill timer must be deleted too */
1424 				(void)del_timer(&sl->outfill_timer);
1425 			printk(KERN_DEBUG "%s: no packets received during keepalive timeout, hangup.\n", sl->dev->name);
1426 			/* this must hangup tty & close slip */
1427 			tty_hangup(sl->tty);
1428 			/* I think we need not something else */
1429 			goto out;
1430 		} else
1431 			set_bit(SLF_KEEPTEST, &sl->flags);
1432 
1433 		mod_timer(&sl->keepalive_timer, jiffies+sl->keepalive*HZ);
1434 	}
1435 out:
1436 	spin_unlock(&sl->lock);
1437 }
1438 
1439 #endif
1440 MODULE_DESCRIPTION("SLIP (serial line) protocol module");
1441 MODULE_LICENSE("GPL");
1442 MODULE_ALIAS_LDISC(N_SLIP);
1443