summaryrefslogtreecommitdiff
path: root/drivers/net/slhc.c
blob: 24bbe00852b29388c5b0cfc78269ce17bd88f0a4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
/*
 * Routines to compress and uncompress tcp packets (for transmission
 * over low speed serial lines).
 *
 * Copyright (c) 1989 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
 *	- Initial distribution.
 *
 *
 * modified for KA9Q Internet Software Package by
 * Katie Stevens (dkstevens@ucdavis.edu)
 * University of California, Davis
 * Computing Services
 *	- 01-31-90	initial adaptation (from 1.19)
 *	PPP.05	02-15-90 [ks]
 *	PPP.08	05-02-90 [ks]	use PPP protocol field to signal compression
 *	PPP.15	09-90	 [ks]	improve mbuf handling
 *	PPP.16	11-02	 [karn]	substantially rewritten to use NOS facilities
 *
 *	- Feb 1991	Bill_Simpson@um.cc.umich.edu
 *			variable number of conversation slots
 *			allow zero or one slots
 *			separate routines
 *			status display
 *	- Jul 1994	Dmitry Gorodchanin
 *			Fixes for memory leaks.
 *      - Oct 1994      Dmitry Gorodchanin
 *                      Modularization.
 *	- Jan 1995	Bjorn Ekwall
 *			Use ip_fast_csum from ip.h
 *	- July 1995	Christos A. Polyzols 
 *			Spotted bug in tcp option checking
 *
 *
 *	This module is a difficult issue. It's clearly inet code but it's also clearly
 *	driver code belonging close to PPP and SLIP
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <net/slhc_vj.h>

#ifdef CONFIG_INET
/* Entire module is for IP only */
#include <linux/mm.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/termios.h>
#include <linux/in.h>
#include <linux/fcntl.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <net/ip.h>
#include <net/protocol.h>
#include <net/icmp.h>
#include <net/tcp.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/timer.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <net/checksum.h>
#include <asm/unaligned.h>

static unsigned char *encode(unsigned char *cp, unsigned short n);
static long decode(unsigned char **cpp);
static unsigned char * put16(unsigned char *cp, unsigned short x);
static unsigned short pull16(unsigned char **cpp);

/* Initialize compression data structure
 *	slots must be in range 0 to 255 (zero meaning no compression)
 */
struct slcompress *
slhc_init(int rslots, int tslots)
{
	register short i;
	register struct cstate *ts;
	struct slcompress *comp;

	comp = kzalloc(sizeof(struct slcompress), GFP_KERNEL);
	if (! comp)
		goto out_fail;

	if ( rslots > 0  &&  rslots < 256 ) {
		size_t rsize = rslots * sizeof(struct cstate);
		comp->rstate = kzalloc(rsize, GFP_KERNEL);
		if (! comp->rstate)
			goto out_free;
		comp->rslot_limit = rslots - 1;
	}

	if ( tslots > 0  &&  tslots < 256 ) {
		size_t tsize = tslots * sizeof(struct cstate);
		comp->tstate = kzalloc(tsize, GFP_KERNEL);
		if (! comp->tstate)
			goto out_free2;
		comp->tslot_limit = tslots - 1;
	}

	comp->xmit_oldest = 0;
	comp->xmit_current = 255;
	comp->recv_current = 255;
	/*
	 * don't accept any packets with implicit index until we get
	 * one with an explicit index.  Otherwise the uncompress code
	 * will try to use connection 255, which is almost certainly
	 * out of range
	 */
	comp->flags |= SLF_TOSS;

	if ( tslots > 0 ) {
		ts = comp->tstate;
		for(i = comp->tslot_limit; i > 0; --i){
			ts[i].cs_this = i;
			ts[i].next = &(ts[i - 1]);
		}
		ts[0].next = &(ts[comp->tslot_limit]);
		ts[0].cs_this = 0;
	}
	return comp;

out_free2:
	kfree(comp->rstate);
out_free:
	kfree(comp);
out_fail:
	return NULL;
}


/* Free a compression data structure */
void
slhc_free(struct slcompress *comp)
{
	if ( comp == NULLSLCOMPR )
		return;

	if ( comp->tstate != NULLSLSTATE )
		kfree( comp->tstate );

	if ( comp->rstate != NULLSLSTATE )
		kfree( comp->rstate );

	kfree( comp );
}


/* Put a short in host order into a char array in network order */
static inline unsigned char *
put16(unsigned char *cp, unsigned short x)
{
	*cp++ = x >> 8;
	*cp++ = x;

	return cp;
}


/* Encode a number */
unsigned char *
encode(unsigned char *cp, unsigned short n)
{
	if(n >= 256 || n == 0){
		*cp++ = 0;
		cp = put16(cp,n);
	} else {
		*cp++ = n;
	}
	return cp;
}

/* Pull a 16-bit integer in host order from buffer in network byte order */
static unsigned short
pull16(unsigned char **cpp)
{
	short rval;

	rval = *(*cpp)++;
	rval <<= 8;
	rval |= *(*cpp)++;
	return rval;
}

/* Decode a number */
long
decode(unsigned char **cpp)
{
	register int x;

	x = *(*cpp)++;
	if(x == 0){
		return pull16(cpp) & 0xffff;	/* pull16 returns -1 on error */
	} else {
		return x & 0xff;		/* -1 if PULLCHAR returned error */
	}
}

/*
 * icp and isize are the original packet.
 * ocp is a place to put a copy if necessary.
 * cpp is initially a pointer to icp.  If the copy is used,
 *    change it to ocp.
 */

int
slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
	unsigned char *ocp, unsigned char **cpp, int compress_cid)
{
	register struct cstate *ocs = &(comp->tstate[comp->xmit_oldest]);
	register struct cstate *lcs = ocs;
	register struct cstate *cs = lcs->next;
	register unsigned long deltaS, deltaA;
	register short changes = 0;
	int hlen;
	unsigned char new_seq[16];
	register unsigned char *cp = new_seq;
	struct iphdr *ip;
	struct tcphdr *th, *oth;


	/*
	 *	Don't play with runt packets.
	 */
	 
	if(isize<sizeof(struct iphdr))
		return isize;
		
	ip = (struct iphdr *) icp;

	/* Bail if this packet isn't TCP, or is an IP fragment */
	if (ip->protocol != IPPROTO_TCP || (ntohs(ip->frag_off) & 0x3fff)) {
		/* Send as regular IP */
		if(ip->protocol != IPPROTO_TCP)
			comp->sls_o_nontcp++;
		else
			comp->sls_o_tcp++;
		return isize;
	}
	/* Extract TCP header */

	th = (struct tcphdr *)(((unsigned char *)ip) + ip->ihl*4);
	hlen = ip->ihl*4 + th->doff*4;

	/*  Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
	 *  some other control bit is set). Also uncompressible if
	 *  it's a runt.
	 */
	if(hlen > isize || th->syn || th->fin || th->rst ||
	    ! (th->ack)){
		/* TCP connection stuff; send as regular IP */
		comp->sls_o_tcp++;
		return isize;
	}
	/*
	 * Packet is compressible -- we're going to send either a
	 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way,
	 * we need to locate (or create) the connection state.
	 *
	 * States are kept in a circularly linked list with
	 * xmit_oldest pointing to the end of the list.  The
	 * list is kept in lru order by moving a state to the
	 * head of the list whenever it is referenced.  Since
	 * the list is short and, empirically, the connection
	 * we want is almost always near the front, we locate
	 * states via linear search.  If we don't find a state
	 * for the datagram, the oldest state is (re-)used.
	 */
	for ( ; ; ) {
		if( ip->saddr == cs->cs_ip.saddr
		 && ip->daddr == cs->cs_ip.daddr
		 && th->source == cs->cs_tcp.source
		 && th->dest == cs->cs_tcp.dest)
			goto found;

		/* if current equal oldest, at end of list */
		if ( cs == ocs )
			break;
		lcs = cs;
		cs = cs->next;
		comp->sls_o_searches++;
	};
	/*
	 * Didn't find it -- re-use oldest cstate.  Send an
	 * uncompressed packet that tells the other side what
	 * connection number we're using for this conversation.
	 *
	 * Note that since the state list is circular, the oldest
	 * state points to the newest and we only need to set
	 * xmit_oldest to update the lru linkage.
	 */
	comp->sls_o_misses++;
	comp->xmit_oldest = lcs->cs_this;
	goto uncompressed;

found:
	/*
	 * Found it -- move to the front on the connection list.
	 */
	if(lcs == ocs) {
 		/* found at most recently used */
	} else if (cs == ocs) {
		/* found at least recently used */
		comp->xmit_oldest = lcs->cs_this;
	} else {
		/* more than 2 elements */
		lcs->next = cs->next;
		cs->next = ocs->next;
		ocs->next = cs;
	}

	/*
	 * Make sure that only what we expect to change changed.
	 * Check the following:
	 * IP protocol version, header length & type of service.
	 * The "Don't fragment" bit.
	 * The time-to-live field.
	 * The TCP header length.
	 * IP options, if any.
	 * TCP options, if any.
	 * If any of these things are different between the previous &
	 * current datagram, we send the current datagram `uncompressed'.
	 */
	oth = &cs->cs_tcp;

	if(ip->version != cs->cs_ip.version || ip->ihl != cs->cs_ip.ihl
	 || ip->tos != cs->cs_ip.tos
	 || (ip->frag_off & htons(0x4000)) != (cs->cs_ip.frag_off & htons(0x4000))
	 || ip->ttl != cs->cs_ip.ttl
	 || th->doff != cs->cs_tcp.doff
	 || (ip->ihl > 5 && memcmp(ip+1,cs->cs_ipopt,((ip->ihl)-5)*4) != 0)
	 || (th->doff > 5 && memcmp(th+1,cs->cs_tcpopt,((th->doff)-5)*4) != 0)){
		goto uncompressed;
	}

	/*
	 * Figure out which of the changing fields changed.  The
	 * receiver expects changes in the order: urgent, window,
	 * ack, seq (the order minimizes the number of temporaries
	 * needed in this section of code).
	 */
	if(th->urg){
		deltaS = ntohs(th->urg_ptr);
		cp = encode(cp,deltaS);
		changes |= NEW_U;
	} else if(th->urg_ptr != oth->urg_ptr){
		/* argh! URG not set but urp changed -- a sensible
		 * implementation should never do this but RFC793
		 * doesn't prohibit the change so we have to deal
		 * with it. */
		goto uncompressed;
	}
	if((deltaS = ntohs(th->window) - ntohs(oth->window)) != 0){
		cp = encode(cp,deltaS);
		changes |= NEW_W;
	}
	if((deltaA = ntohl(th->ack_seq) - ntohl(oth->ack_seq)) != 0L){
		if(deltaA > 0x0000ffff)
			goto uncompressed;
		cp = encode(cp,deltaA);
		changes |= NEW_A;
	}
	if((deltaS = ntohl(th->seq) - ntohl(oth->seq)) != 0L){
		if(deltaS > 0x0000ffff)
			goto uncompressed;
		cp = encode(cp,deltaS);
		changes |= NEW_S;
	}

	switch(changes){
	case 0:	/* Nothing changed. If this packet contains data and the
		 * last one didn't, this is probably a data packet following
		 * an ack (normal on an interactive connection) and we send
		 * it compressed.  Otherwise it's probably a retransmit,
		 * retransmitted ack or window probe.  Send it uncompressed
		 * in case the other side missed the compressed version.
		 */
		if(ip->tot_len != cs->cs_ip.tot_len &&
		   ntohs(cs->cs_ip.tot_len) == hlen)
			break;
		goto uncompressed;
		break;
	case SPECIAL_I:
	case SPECIAL_D:
		/* actual changes match one of our special case encodings --
		 * send packet uncompressed.
		 */
		goto uncompressed;
	case NEW_S|NEW_A:
		if(deltaS == deltaA &&
		    deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
			/* special case for echoed terminal traffic */
			changes = SPECIAL_I;
			cp = new_seq;
		}
		break;
	case NEW_S:
		if(deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
			/* special case for data xfer */
			changes = SPECIAL_D;
			cp = new_seq;
		}
		break;
	}
	deltaS = ntohs(ip->id) - ntohs(cs->cs_ip.id);
	if(deltaS != 1){
		cp = encode(cp,deltaS);
		changes |= NEW_I;
	}
	if(th->psh)
		changes |= TCP_PUSH_BIT;
	/* Grab the cksum before we overwrite it below.  Then update our
	 * state with this packet's header.
	 */
	deltaA = ntohs(th->check);
	memcpy(&cs->cs_ip,ip,20);
	memcpy(&cs->cs_tcp,th,20);
	/* We want to use the original packet as our compressed packet.
	 * (cp - new_seq) is the number of bytes we need for compressed
	 * sequence numbers.  In addition we need one byte for the change
	 * mask, one for the connection id and two for the tcp checksum.
	 * So, (cp - new_seq) + 4 bytes of header are needed.
	 */
	deltaS = cp - new_seq;
	if(compress_cid == 0 || comp->xmit_current != cs->cs_this){
		cp = ocp;
		*cpp = ocp;
		*cp++ = changes | NEW_C;
		*cp++ = cs->cs_this;
		comp->xmit_current = cs->cs_this;
	} else {
		cp = ocp;
		*cpp = ocp;
		*cp++ = changes;
	}
	cp = put16(cp,(short)deltaA);	/* Write TCP checksum */
/* deltaS is now the size of the change section of the compressed header */
	memcpy(cp,new_seq,deltaS);	/* Write list of deltas */
	memcpy(cp+deltaS,icp+hlen,isize-hlen);
	comp->sls_o_compressed++;
	ocp[0] |= SL_TYPE_COMPRESSED_TCP;
	return isize - hlen + deltaS + (cp - ocp);

	/* Update connection state cs & send uncompressed packet (i.e.,
	 * a regular ip/tcp packet but with the 'conversation id' we hope
	 * to use on future compressed packets in the protocol field).
	 */
uncompressed:
	memcpy(&cs->cs_ip,ip,20);
	memcpy(&cs->cs_tcp,th,20);
	if (ip->ihl > 5)
	  memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);
	if (th->doff > 5)
	  memcpy(cs->cs_tcpopt, th+1, ((th->doff) - 5) * 4);
	comp->xmit_current = cs->cs_this;
	comp->sls_o_uncompressed++;
	memcpy(ocp, icp, isize);
	*cpp = ocp;
	ocp[9] = cs->cs_this;
	ocp[0] |= SL_TYPE_UNCOMPRESSED_TCP;
	return isize;
}


int
slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
{
	register int changes;
	long x;
	register struct tcphdr *thp;
	register struct iphdr *ip;
	register struct cstate *cs;
	int len, hdrlen;
	unsigned char *cp = icp;

	/* We've got a compressed packet; read the change byte */
	comp->sls_i_compressed++;
	if(isize < 3){
		comp->sls_i_error++;
		return 0;
	}
	changes = *cp++;
	if(changes & NEW_C){
		/* Make sure the state index is in range, then grab the state.
		 * If we have a good state index, clear the 'discard' flag.
		 */
		x = *cp++;	/* Read conn index */
		if(x < 0 || x > comp->rslot_limit)
			goto bad;

		comp->flags &=~ SLF_TOSS;
		comp->recv_current = x;
	} else {
		/* this packet has an implicit state index.  If we've
		 * had a line error since the last time we got an
		 * explicit state index, we have to toss the packet. */
		if(comp->flags & SLF_TOSS){
			comp->sls_i_tossed++;
			return 0;
		}
	}
	cs = &comp->rstate[comp->recv_current];
	thp = &cs->cs_tcp;
	ip = &cs->cs_ip;

	if((x = pull16(&cp)) == -1) {	/* Read the TCP checksum */
		goto bad;
        }
	thp->check = htons(x);

	thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
/*
 * we can use the same number for the length of the saved header and
 * the current one, because the packet wouldn't have been sent
 * as compressed unless the options were the same as the previous one
 */

	hdrlen = ip->ihl * 4 + thp->doff * 4;

	switch(changes & SPECIALS_MASK){
	case SPECIAL_I:		/* Echoed terminal traffic */
		{
		register short i;
		i = ntohs(ip->tot_len) - hdrlen;
		thp->ack_seq = htonl( ntohl(thp->ack_seq) + i);
		thp->seq = htonl( ntohl(thp->seq) + i);
		}
		break;

	case SPECIAL_D:			/* Unidirectional data */
		thp->seq = htonl( ntohl(thp->seq) +
				  ntohs(ip->tot_len) - hdrlen);
		break;

	default:
		if(changes & NEW_U){
			thp->urg = 1;
			if((x = decode(&cp)) == -1) {
				goto bad;
			}
			thp->urg_ptr = htons(x);
		} else
			thp->urg = 0;
		if(changes & NEW_W){
			if((x = decode(&cp)) == -1) {
				goto bad;
			}
			thp->window = htons( ntohs(thp->window) + x);
		}
		if(changes & NEW_A){
			if((x = decode(&cp)) == -1) {
				goto bad;
			}
			thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);
		}
		if(changes & NEW_S){
			if((x = decode(&cp)) == -1) {
				goto bad;
			}
			thp->seq = htonl( ntohl(thp->seq) + x);
		}
		break;
	}
	if(changes & NEW_I){
		if((x = decode(&cp)) == -1) {
			goto bad;
		}
		ip->id = htons (ntohs (ip->id) + x);
	} else
		ip->id = htons (ntohs (ip->id) + 1);

	/*
	 * At this point, cp points to the first byte of data in the
	 * packet.  Put the reconstructed TCP and IP headers back on the
	 * packet.  Recalculate IP checksum (but not TCP checksum).
	 */

	len = isize - (cp - icp);
	if (len < 0)
		goto bad;
	len += hdrlen;
	ip->tot_len = htons(len);
	ip->check = 0;

	memmove(icp + hdrlen, cp, len - hdrlen);

	cp = icp;
	memcpy(cp, ip, 20);
	cp += 20;

	if (ip->ihl > 5) {
	  memcpy(cp, cs->cs_ipopt, (ip->ihl - 5) * 4);
	  cp += (ip->ihl - 5) * 4;
	}

	put_unaligned(ip_fast_csum(icp, ip->ihl),
		      &((struct iphdr *)icp)->check);

	memcpy(cp, thp, 20);
	cp += 20;

	if (thp->doff > 5) {
	  memcpy(cp, cs->cs_tcpopt, ((thp->doff) - 5) * 4);
	  cp += ((thp->doff) - 5) * 4;
	}

	return len;
bad:
	comp->sls_i_error++;
	return slhc_toss( comp );
}


int
slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
{
	register struct cstate *cs;
	unsigned ihl;

	unsigned char index;

	if(isize < 20) {
		/* The packet is shorter than a legal IP header */
		comp->sls_i_runt++;
		return slhc_toss( comp );
	}
	/* Peek at the IP header's IHL field to find its length */
	ihl = icp[0] & 0xf;
	if(ihl < 20 / 4){
		/* The IP header length field is too small */
		comp->sls_i_runt++;
		return slhc_toss( comp );
	}
	index = icp[9];
	icp[9] = IPPROTO_TCP;

	if (ip_fast_csum(icp, ihl)) {
		/* Bad IP header checksum; discard */
		comp->sls_i_badcheck++;
		return slhc_toss( comp );
	}
	if(index > comp->rslot_limit) {
		comp->sls_i_error++;
		return slhc_toss(comp);
	}

	/* Update local state */
	cs = &comp->rstate[comp->recv_current = index];
	comp->flags &=~ SLF_TOSS;
	memcpy(&cs->cs_ip,icp,20);
	memcpy(&cs->cs_tcp,icp + ihl*4,20);
	if (ihl > 5)
	  memcpy(cs->cs_ipopt, icp + sizeof(struct iphdr), (ihl - 5) * 4);
	if (cs->cs_tcp.doff > 5)
	  memcpy(cs->cs_tcpopt, icp + ihl*4 + sizeof(struct tcphdr), (cs->cs_tcp.doff - 5) * 4);
	cs->cs_hsize = ihl*2 + cs->cs_tcp.doff*2;
	/* Put headers back on packet
	 * Neither header checksum is recalculated
	 */
	comp->sls_i_uncompressed++;
	return isize;
}

int
slhc_toss(struct slcompress *comp)
{
	if ( comp == NULLSLCOMPR )
		return 0;

	comp->flags |= SLF_TOSS;
	return 0;
}


/* VJ header compression */
EXPORT_SYMBOL(slhc_init);
EXPORT_SYMBOL(slhc_free);
EXPORT_SYMBOL(slhc_remember);
EXPORT_SYMBOL(slhc_compress);
EXPORT_SYMBOL(slhc_uncompress);
EXPORT_SYMBOL(slhc_toss);

#ifdef MODULE

int init_module(void)
{
	printk(KERN_INFO "CSLIP: code copyright 1989 Regents of the University of California\n");
	return 0;
}

void cleanup_module(void)
{
	return;
}

#endif /* MODULE */
#else /* CONFIG_INET */


int
slhc_toss(struct slcompress *comp)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_toss");
  return -EINVAL;
}
int
slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_uncompress");
  return -EINVAL;
}
int
slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
	unsigned char *ocp, unsigned char **cpp, int compress_cid)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_compress");
  return -EINVAL;
}

int
slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_remember");
  return -EINVAL;
}

void
slhc_free(struct slcompress *comp)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_free");
  return;
}
struct slcompress *
slhc_init(int rslots, int tslots)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_init");
  return NULL;
}
EXPORT_SYMBOL(slhc_init);
EXPORT_SYMBOL(slhc_free);
EXPORT_SYMBOL(slhc_remember);
EXPORT_SYMBOL(slhc_compress);
EXPORT_SYMBOL(slhc_uncompress);
EXPORT_SYMBOL(slhc_toss);

#endif /* CONFIG_INET */
MODULE_LICENSE("Dual BSD/GPL");