slcan.c revision 2bf3440d7b8755f2627232e6a4c37efbbe053685 
1/*
2 * slcan.c - serial line CAN interface driver (using tty line discipline)
3 *
4 * This file is derived from linux/drivers/net/slip/slip.c
5 *
6 * slip.c Authors  : Laurence Culhane <loz@holmes.demon.co.uk>
7 *                   Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
8 * slcan.c Author  : Oliver Hartkopp <socketcan@hartkopp.net>
9 *
10 * This program is free software; you can redistribute it and/or modify it
11 * under the terms of the GNU General Public License as published by the
12 * Free Software Foundation; either version 2 of the License, or (at your
13 * option) any later version.
14 *
15 * This program is distributed in the hope that it will be useful, but
16 * WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 * General Public License for more details.
19 *
20 * You should have received a copy of the GNU General Public License along
21 * with this program; if not, write to the Free Software Foundation, Inc.,
22 * 59 Temple Place, Suite 330, Boston, MA 02111-1307. You can also get it
23 * at http://www.gnu.org/licenses/gpl.html
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
26 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
27 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
28 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
29 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
35 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
36 * DAMAGE.
37 *
38 */
39
40#include <linux/module.h>
41#include <linux/moduleparam.h>
42
43#include <linux/uaccess.h>
44#include <linux/bitops.h>
45#include <linux/string.h>
46#include <linux/tty.h>
47#include <linux/errno.h>
48#include <linux/netdevice.h>
49#include <linux/skbuff.h>
50#include <linux/rtnetlink.h>
51#include <linux/if_arp.h>
52#include <linux/if_ether.h>
53#include <linux/sched.h>
54#include <linux/delay.h>
55#include <linux/init.h>
56#include <linux/kernel.h>
57#include <linux/can.h>
58#include <linux/can/skb.h>
59
60static __initconst const char banner[] =
61	KERN_INFO "slcan: serial line CAN interface driver\n";
62
63MODULE_ALIAS_LDISC(N_SLCAN);
64MODULE_DESCRIPTION("serial line CAN interface");
65MODULE_LICENSE("GPL");
66MODULE_AUTHOR("Oliver Hartkopp <socketcan@hartkopp.net>");
67
68#define SLCAN_MAGIC 0x53CA
69
70static int maxdev = 10;		/* MAX number of SLCAN channels;
71				   This can be overridden with
72				   insmod slcan.ko maxdev=nnn	*/
73module_param(maxdev, int, 0);
74MODULE_PARM_DESC(maxdev, "Maximum number of slcan interfaces");
75
76/* maximum rx buffer len: extended CAN frame with timestamp */
77#define SLC_MTU (sizeof("T1111222281122334455667788EA5F\r")+1)
78
79struct slcan {
80	int			magic;
81
82	/* Various fields. */
83	struct tty_struct	*tty;		/* ptr to TTY structure	     */
84	struct net_device	*dev;		/* easy for intr handling    */
85	spinlock_t		lock;
86
87	/* These are pointers to the malloc()ed frame buffers. */
88	unsigned char		rbuff[SLC_MTU];	/* receiver buffer	     */
89	int			rcount;         /* received chars counter    */
90	unsigned char		xbuff[SLC_MTU];	/* transmitter buffer	     */
91	unsigned char		*xhead;         /* pointer to next XMIT byte */
92	int			xleft;          /* bytes left in XMIT queue  */
93
94	unsigned long		flags;		/* Flag values/ mode etc     */
95#define SLF_INUSE		0		/* Channel in use            */
96#define SLF_ERROR		1               /* Parity, etc. error        */
97};
98
99static struct net_device **slcan_devs;
100
101 /************************************************************************
102  *			SLCAN ENCAPSULATION FORMAT			 *
103  ************************************************************************/
104
105/*
106 * A CAN frame has a can_id (11 bit standard frame format OR 29 bit extended
107 * frame format) a data length code (can_dlc) which can be from 0 to 8
108 * and up to <can_dlc> data bytes as payload.
109 * Additionally a CAN frame may become a remote transmission frame if the
110 * RTR-bit is set. This causes another ECU to send a CAN frame with the
111 * given can_id.
112 *
113 * The SLCAN ASCII representation of these different frame types is:
114 * <type> <id> <dlc> <data>*
115 *
116 * Extended frames (29 bit) are defined by capital characters in the type.
117 * RTR frames are defined as 'r' types - normal frames have 't' type:
118 * t => 11 bit data frame
119 * r => 11 bit RTR frame
120 * T => 29 bit data frame
121 * R => 29 bit RTR frame
122 *
123 * The <id> is 3 (standard) or 8 (extended) bytes in ASCII Hex (base64).
124 * The <dlc> is a one byte ASCII number ('0' - '8')
125 * The <data> section has at much ASCII Hex bytes as defined by the <dlc>
126 *
127 * Examples:
128 *
129 * t1230 : can_id 0x123, can_dlc 0, no data
130 * t4563112233 : can_id 0x456, can_dlc 3, data 0x11 0x22 0x33
131 * T12ABCDEF2AA55 : extended can_id 0x12ABCDEF, can_dlc 2, data 0xAA 0x55
132 * r1230 : can_id 0x123, can_dlc 0, no data, remote transmission request
133 *
134 */
135
136 /************************************************************************
137  *			STANDARD SLCAN DECAPSULATION			 *
138  ************************************************************************/
139
140/* Send one completely decapsulated can_frame to the network layer */
141static void slc_bump(struct slcan *sl)
142{
143	struct sk_buff *skb;
144	struct can_frame cf;
145	int i, dlc_pos, tmp;
146	unsigned long ultmp;
147	char cmd = sl->rbuff[0];
148
149	if ((cmd != 't') && (cmd != 'T') && (cmd != 'r') && (cmd != 'R'))
150		return;
151
152	if (cmd & 0x20) /* tiny chars 'r' 't' => standard frame format */
153		dlc_pos = 4; /* dlc position tiiid */
154	else
155		dlc_pos = 9; /* dlc position Tiiiiiiiid */
156
157	if (!((sl->rbuff[dlc_pos] >= '0') && (sl->rbuff[dlc_pos] < '9')))
158		return;
159
160	cf.can_dlc = sl->rbuff[dlc_pos] - '0'; /* get can_dlc from ASCII val */
161
162	sl->rbuff[dlc_pos] = 0; /* terminate can_id string */
163
164	if (strict_strtoul(sl->rbuff+1, 16, &ultmp))
165		return;
166
167	cf.can_id = ultmp;
168
169	if (!(cmd & 0x20)) /* NO tiny chars => extended frame format */
170		cf.can_id |= CAN_EFF_FLAG;
171
172	if ((cmd | 0x20) == 'r') /* RTR frame */
173		cf.can_id |= CAN_RTR_FLAG;
174
175	*(u64 *) (&cf.data) = 0; /* clear payload */
176
177	for (i = 0, dlc_pos++; i < cf.can_dlc; i++) {
178		tmp = hex_to_bin(sl->rbuff[dlc_pos++]);
179		if (tmp < 0)
180			return;
181		cf.data[i] = (tmp << 4);
182		tmp = hex_to_bin(sl->rbuff[dlc_pos++]);
183		if (tmp < 0)
184			return;
185		cf.data[i] |= tmp;
186	}
187
188	skb = dev_alloc_skb(sizeof(struct can_frame) +
189			    sizeof(struct can_skb_priv));
190	if (!skb)
191		return;
192
193	skb->dev = sl->dev;
194	skb->protocol = htons(ETH_P_CAN);
195	skb->pkt_type = PACKET_BROADCAST;
196	skb->ip_summed = CHECKSUM_UNNECESSARY;
197
198	can_skb_reserve(skb);
199	can_skb_prv(skb)->ifindex = sl->dev->ifindex;
200
201	memcpy(skb_put(skb, sizeof(struct can_frame)),
202	       &cf, sizeof(struct can_frame));
203	netif_rx_ni(skb);
204
205	sl->dev->stats.rx_packets++;
206	sl->dev->stats.rx_bytes += cf.can_dlc;
207}
208
209/* parse tty input stream */
210static void slcan_unesc(struct slcan *sl, unsigned char s)
211{
212
213	if ((s == '\r') || (s == '\a')) { /* CR or BEL ends the pdu */
214		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
215		    (sl->rcount > 4))  {
216			slc_bump(sl);
217		}
218		sl->rcount = 0;
219	} else {
220		if (!test_bit(SLF_ERROR, &sl->flags))  {
221			if (sl->rcount < SLC_MTU)  {
222				sl->rbuff[sl->rcount++] = s;
223				return;
224			} else {
225				sl->dev->stats.rx_over_errors++;
226				set_bit(SLF_ERROR, &sl->flags);
227			}
228		}
229	}
230}
231
232 /************************************************************************
233  *			STANDARD SLCAN ENCAPSULATION			 *
234  ************************************************************************/
235
236/* Encapsulate one can_frame and stuff into a TTY queue. */
237static void slc_encaps(struct slcan *sl, struct can_frame *cf)
238{
239	int actual, idx, i;
240	char cmd;
241
242	if (cf->can_id & CAN_RTR_FLAG)
243		cmd = 'R'; /* becomes 'r' in standard frame format */
244	else
245		cmd = 'T'; /* becomes 't' in standard frame format */
246
247	if (cf->can_id & CAN_EFF_FLAG)
248		sprintf(sl->xbuff, "%c%08X%d", cmd,
249			cf->can_id & CAN_EFF_MASK, cf->can_dlc);
250	else
251		sprintf(sl->xbuff, "%c%03X%d", cmd | 0x20,
252			cf->can_id & CAN_SFF_MASK, cf->can_dlc);
253
254	idx = strlen(sl->xbuff);
255
256	for (i = 0; i < cf->can_dlc; i++)
257		sprintf(&sl->xbuff[idx + 2*i], "%02X", cf->data[i]);
258
259	strcat(sl->xbuff, "\r"); /* add terminating character */
260
261	/* Order of next two lines is *very* important.
262	 * When we are sending a little amount of data,
263	 * the transfer may be completed inside the ops->write()
264	 * routine, because it's running with interrupts enabled.
265	 * In this case we *never* got WRITE_WAKEUP event,
266	 * if we did not request it before write operation.
267	 *       14 Oct 1994  Dmitry Gorodchanin.
268	 */
269	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
270	actual = sl->tty->ops->write(sl->tty, sl->xbuff, strlen(sl->xbuff));
271	sl->xleft = strlen(sl->xbuff) - actual;
272	sl->xhead = sl->xbuff + actual;
273	sl->dev->stats.tx_bytes += cf->can_dlc;
274}
275
276/*
277 * Called by the driver when there's room for more data.  If we have
278 * more packets to send, we send them here.
279 */
280static void slcan_write_wakeup(struct tty_struct *tty)
281{
282	int actual;
283	struct slcan *sl = (struct slcan *) tty->disc_data;
284
285	/* First make sure we're connected. */
286	if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
287		return;
288
289	if (sl->xleft <= 0)  {
290		/* Now serial buffer is almost free & we can start
291		 * transmission of another packet */
292		sl->dev->stats.tx_packets++;
293		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
294		netif_wake_queue(sl->dev);
295		return;
296	}
297
298	actual = tty->ops->write(tty, sl->xhead, sl->xleft);
299	sl->xleft -= actual;
300	sl->xhead += actual;
301}
302
303/* Send a can_frame to a TTY queue. */
304static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
305{
306	struct slcan *sl = netdev_priv(dev);
307
308	if (skb->len != sizeof(struct can_frame))
309		goto out;
310
311	spin_lock(&sl->lock);
312	if (!netif_running(dev))  {
313		spin_unlock(&sl->lock);
314		printk(KERN_WARNING "%s: xmit: iface is down\n", dev->name);
315		goto out;
316	}
317	if (sl->tty == NULL) {
318		spin_unlock(&sl->lock);
319		goto out;
320	}
321
322	netif_stop_queue(sl->dev);
323	slc_encaps(sl, (struct can_frame *) skb->data); /* encaps & send */
324	spin_unlock(&sl->lock);
325
326out:
327	kfree_skb(skb);
328	return NETDEV_TX_OK;
329}
330
331
332/******************************************
333 *   Routines looking at netdevice side.
334 ******************************************/
335
336/* Netdevice UP -> DOWN routine */
337static int slc_close(struct net_device *dev)
338{
339	struct slcan *sl = netdev_priv(dev);
340
341	spin_lock_bh(&sl->lock);
342	if (sl->tty) {
343		/* TTY discipline is running. */
344		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
345	}
346	netif_stop_queue(dev);
347	sl->rcount   = 0;
348	sl->xleft    = 0;
349	spin_unlock_bh(&sl->lock);
350
351	return 0;
352}
353
354/* Netdevice DOWN -> UP routine */
355static int slc_open(struct net_device *dev)
356{
357	struct slcan *sl = netdev_priv(dev);
358
359	if (sl->tty == NULL)
360		return -ENODEV;
361
362	sl->flags &= (1 << SLF_INUSE);
363	netif_start_queue(dev);
364	return 0;
365}
366
367/* Hook the destructor so we can free slcan devs at the right point in time */
368static void slc_free_netdev(struct net_device *dev)
369{
370	int i = dev->base_addr;
371	free_netdev(dev);
372	slcan_devs[i] = NULL;
373}
374
375static const struct net_device_ops slc_netdev_ops = {
376	.ndo_open               = slc_open,
377	.ndo_stop               = slc_close,
378	.ndo_start_xmit         = slc_xmit,
379};
380
381static void slc_setup(struct net_device *dev)
382{
383	dev->netdev_ops		= &slc_netdev_ops;
384	dev->destructor		= slc_free_netdev;
385
386	dev->hard_header_len	= 0;
387	dev->addr_len		= 0;
388	dev->tx_queue_len	= 10;
389
390	dev->mtu		= sizeof(struct can_frame);
391	dev->type		= ARPHRD_CAN;
392
393	/* New-style flags. */
394	dev->flags		= IFF_NOARP;
395	dev->features           = NETIF_F_HW_CSUM;
396}
397
398/******************************************
399  Routines looking at TTY side.
400 ******************************************/
401
402/*
403 * Handle the 'receiver data ready' interrupt.
404 * This function is called by the 'tty_io' module in the kernel when
405 * a block of SLCAN data has been received, which can now be decapsulated
406 * and sent on to some IP layer for further processing. This will not
407 * be re-entered while running but other ldisc functions may be called
408 * in parallel
409 */
410
411static void slcan_receive_buf(struct tty_struct *tty,
412			      const unsigned char *cp, char *fp, int count)
413{
414	struct slcan *sl = (struct slcan *) tty->disc_data;
415
416	if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
417		return;
418
419	/* Read the characters out of the buffer */
420	while (count--) {
421		if (fp && *fp++) {
422			if (!test_and_set_bit(SLF_ERROR, &sl->flags))
423				sl->dev->stats.rx_errors++;
424			cp++;
425			continue;
426		}
427		slcan_unesc(sl, *cp++);
428	}
429}
430
431/************************************
432 *  slcan_open helper routines.
433 ************************************/
434
435/* Collect hanged up channels */
436static void slc_sync(void)
437{
438	int i;
439	struct net_device *dev;
440	struct slcan	  *sl;
441
442	for (i = 0; i < maxdev; i++) {
443		dev = slcan_devs[i];
444		if (dev == NULL)
445			break;
446
447		sl = netdev_priv(dev);
448		if (sl->tty)
449			continue;
450		if (dev->flags & IFF_UP)
451			dev_close(dev);
452	}
453}
454
455/* Find a free SLCAN channel, and link in this `tty' line. */
456static struct slcan *slc_alloc(dev_t line)
457{
458	int i;
459	char name[IFNAMSIZ];
460	struct net_device *dev = NULL;
461	struct slcan       *sl;
462
463	for (i = 0; i < maxdev; i++) {
464		dev = slcan_devs[i];
465		if (dev == NULL)
466			break;
467
468	}
469
470	/* Sorry, too many, all slots in use */
471	if (i >= maxdev)
472		return NULL;
473
474	sprintf(name, "slcan%d", i);
475	dev = alloc_netdev(sizeof(*sl), name, slc_setup);
476	if (!dev)
477		return NULL;
478
479	dev->base_addr  = i;
480	sl = netdev_priv(dev);
481
482	/* Initialize channel control data */
483	sl->magic = SLCAN_MAGIC;
484	sl->dev	= dev;
485	spin_lock_init(&sl->lock);
486	slcan_devs[i] = dev;
487
488	return sl;
489}
490
491/*
492 * Open the high-level part of the SLCAN channel.
493 * This function is called by the TTY module when the
494 * SLCAN line discipline is called for.  Because we are
495 * sure the tty line exists, we only have to link it to
496 * a free SLCAN channel...
497 *
498 * Called in process context serialized from other ldisc calls.
499 */
500
501static int slcan_open(struct tty_struct *tty)
502{
503	struct slcan *sl;
504	int err;
505
506	if (!capable(CAP_NET_ADMIN))
507		return -EPERM;
508
509	if (tty->ops->write == NULL)
510		return -EOPNOTSUPP;
511
512	/* RTnetlink lock is misused here to serialize concurrent
513	   opens of slcan channels. There are better ways, but it is
514	   the simplest one.
515	 */
516	rtnl_lock();
517
518	/* Collect hanged up channels. */
519	slc_sync();
520
521	sl = tty->disc_data;
522
523	err = -EEXIST;
524	/* First make sure we're not already connected. */
525	if (sl && sl->magic == SLCAN_MAGIC)
526		goto err_exit;
527
528	/* OK.  Find a free SLCAN channel to use. */
529	err = -ENFILE;
530	sl = slc_alloc(tty_devnum(tty));
531	if (sl == NULL)
532		goto err_exit;
533
534	sl->tty = tty;
535	tty->disc_data = sl;
536
537	if (!test_bit(SLF_INUSE, &sl->flags)) {
538		/* Perform the low-level SLCAN initialization. */
539		sl->rcount   = 0;
540		sl->xleft    = 0;
541
542		set_bit(SLF_INUSE, &sl->flags);
543
544		err = register_netdevice(sl->dev);
545		if (err)
546			goto err_free_chan;
547	}
548
549	/* Done.  We have linked the TTY line to a channel. */
550	rtnl_unlock();
551	tty->receive_room = 65536;	/* We don't flow control */
552
553	/* TTY layer expects 0 on success */
554	return 0;
555
556err_free_chan:
557	sl->tty = NULL;
558	tty->disc_data = NULL;
559	clear_bit(SLF_INUSE, &sl->flags);
560
561err_exit:
562	rtnl_unlock();
563
564	/* Count references from TTY module */
565	return err;
566}
567
568/*
569 * Close down a SLCAN channel.
570 * This means flushing out any pending queues, and then returning. This
571 * call is serialized against other ldisc functions.
572 *
573 * We also use this method for a hangup event.
574 */
575
576static void slcan_close(struct tty_struct *tty)
577{
578	struct slcan *sl = (struct slcan *) tty->disc_data;
579
580	/* First make sure we're connected. */
581	if (!sl || sl->magic != SLCAN_MAGIC || sl->tty != tty)
582		return;
583
584	tty->disc_data = NULL;
585	sl->tty = NULL;
586
587	/* Flush network side */
588	unregister_netdev(sl->dev);
589	/* This will complete via sl_free_netdev */
590}
591
592static int slcan_hangup(struct tty_struct *tty)
593{
594	slcan_close(tty);
595	return 0;
596}
597
598/* Perform I/O control on an active SLCAN channel. */
599static int slcan_ioctl(struct tty_struct *tty, struct file *file,
600		       unsigned int cmd, unsigned long arg)
601{
602	struct slcan *sl = (struct slcan *) tty->disc_data;
603	unsigned int tmp;
604
605	/* First make sure we're connected. */
606	if (!sl || sl->magic != SLCAN_MAGIC)
607		return -EINVAL;
608
609	switch (cmd) {
610	case SIOCGIFNAME:
611		tmp = strlen(sl->dev->name) + 1;
612		if (copy_to_user((void __user *)arg, sl->dev->name, tmp))
613			return -EFAULT;
614		return 0;
615
616	case SIOCSIFHWADDR:
617		return -EINVAL;
618
619	default:
620		return tty_mode_ioctl(tty, file, cmd, arg);
621	}
622}
623
624static struct tty_ldisc_ops slc_ldisc = {
625	.owner		= THIS_MODULE,
626	.magic		= TTY_LDISC_MAGIC,
627	.name		= "slcan",
628	.open		= slcan_open,
629	.close		= slcan_close,
630	.hangup		= slcan_hangup,
631	.ioctl		= slcan_ioctl,
632	.receive_buf	= slcan_receive_buf,
633	.write_wakeup	= slcan_write_wakeup,
634};
635
636static int __init slcan_init(void)
637{
638	int status;
639
640	if (maxdev < 4)
641		maxdev = 4; /* Sanity */
642
643	printk(banner);
644	printk(KERN_INFO "slcan: %d dynamic interface channels.\n", maxdev);
645
646	slcan_devs = kzalloc(sizeof(struct net_device *)*maxdev, GFP_KERNEL);
647	if (!slcan_devs)
648		return -ENOMEM;
649
650	/* Fill in our line protocol discipline, and register it */
651	status = tty_register_ldisc(N_SLCAN, &slc_ldisc);
652	if (status)  {
653		printk(KERN_ERR "slcan: can't register line discipline\n");
654		kfree(slcan_devs);
655	}
656	return status;
657}
658
659static void __exit slcan_exit(void)
660{
661	int i;
662	struct net_device *dev;
663	struct slcan *sl;
664	unsigned long timeout = jiffies + HZ;
665	int busy = 0;
666
667	if (slcan_devs == NULL)
668		return;
669
670	/* First of all: check for active disciplines and hangup them.
671	 */
672	do {
673		if (busy)
674			msleep_interruptible(100);
675
676		busy = 0;
677		for (i = 0; i < maxdev; i++) {
678			dev = slcan_devs[i];
679			if (!dev)
680				continue;
681			sl = netdev_priv(dev);
682			spin_lock_bh(&sl->lock);
683			if (sl->tty) {
684				busy++;
685				tty_hangup(sl->tty);
686			}
687			spin_unlock_bh(&sl->lock);
688		}
689	} while (busy && time_before(jiffies, timeout));
690
691	/* FIXME: hangup is async so we should wait when doing this second
692	   phase */
693
694	for (i = 0; i < maxdev; i++) {
695		dev = slcan_devs[i];
696		if (!dev)
697			continue;
698		slcan_devs[i] = NULL;
699
700		sl = netdev_priv(dev);
701		if (sl->tty) {
702			printk(KERN_ERR "%s: tty discipline still running\n",
703			       dev->name);
704			/* Intentionally leak the control block. */
705			dev->destructor = NULL;
706		}
707
708		unregister_netdev(dev);
709	}
710
711	kfree(slcan_devs);
712	slcan_devs = NULL;
713
714	i = tty_unregister_ldisc(N_SLCAN);
715	if (i)
716		printk(KERN_ERR "slcan: can't unregister ldisc (err %d)\n", i);
717}
718
719module_init(slcan_init);
720module_exit(slcan_exit);
721