summaryrefslogtreecommitdiffstats
path: root/net/6lowpan/iphc.c
blob: dd5f27d5358eca32d1449e679a1cc9d28635b42d (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
/*
 * Copyright 2011, Siemens AG
 * written by Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
 */

/* Based on patches from Jon Smirl <jonsmirl@gmail.com>
 * Copyright (c) 2011 Jon Smirl <jonsmirl@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

/* Jon's code is based on 6lowpan implementation for Contiki which is:
 * Copyright (c) 2008, Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <linux/bitops.h>
#include <linux/if_arp.h>
#include <linux/netdevice.h>
#include <net/6lowpan.h>
#include <net/ipv6.h>
#include <net/af_ieee802154.h>

#include "nhc.h"

/* Uncompress address function for source and
 * destination address(non-multicast).
 *
 * address_mode is sam value or dam value.
 */
static int uncompress_addr(struct sk_buff *skb,
			   struct in6_addr *ipaddr, const u8 address_mode,
			   const u8 *lladdr, const u8 addr_type,
			   const u8 addr_len)
{
	bool fail;

	switch (address_mode) {
	case LOWPAN_IPHC_ADDR_00:
		/* for global link addresses */
		fail = lowpan_fetch_skb(skb, ipaddr->s6_addr, 16);
		break;
	case LOWPAN_IPHC_ADDR_01:
		/* fe:80::XXXX:XXXX:XXXX:XXXX */
		ipaddr->s6_addr[0] = 0xFE;
		ipaddr->s6_addr[1] = 0x80;
		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[8], 8);
		break;
	case LOWPAN_IPHC_ADDR_02:
		/* fe:80::ff:fe00:XXXX */
		ipaddr->s6_addr[0] = 0xFE;
		ipaddr->s6_addr[1] = 0x80;
		ipaddr->s6_addr[11] = 0xFF;
		ipaddr->s6_addr[12] = 0xFE;
		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[14], 2);
		break;
	case LOWPAN_IPHC_ADDR_03:
		fail = false;
		switch (addr_type) {
		case IEEE802154_ADDR_LONG:
			/* fe:80::XXXX:XXXX:XXXX:XXXX
			 *        \_________________/
			 *              hwaddr
			 */
			ipaddr->s6_addr[0] = 0xFE;
			ipaddr->s6_addr[1] = 0x80;
			memcpy(&ipaddr->s6_addr[8], lladdr, addr_len);
			/* second bit-flip (Universe/Local)
			 * is done according RFC2464
			 */
			ipaddr->s6_addr[8] ^= 0x02;
			break;
		case IEEE802154_ADDR_SHORT:
			/* fe:80::ff:fe00:XXXX
			 *		  \__/
			 *	       short_addr
			 *
			 * Universe/Local bit is zero.
			 */
			ipaddr->s6_addr[0] = 0xFE;
			ipaddr->s6_addr[1] = 0x80;
			ipaddr->s6_addr[11] = 0xFF;
			ipaddr->s6_addr[12] = 0xFE;
			ipaddr->s6_addr16[7] = htons(*((u16 *)lladdr));
			break;
		default:
			pr_debug("Invalid addr_type set\n");
			return -EINVAL;
		}
		break;
	default:
		pr_debug("Invalid address mode value: 0x%x\n", address_mode);
		return -EINVAL;
	}

	if (fail) {
		pr_debug("Failed to fetch skb data\n");
		return -EIO;
	}

	raw_dump_inline(NULL, "Reconstructed ipv6 addr is",
			ipaddr->s6_addr, 16);

	return 0;
}

/* Uncompress address function for source context
 * based address(non-multicast).
 */
static int uncompress_context_based_src_addr(struct sk_buff *skb,
					     struct in6_addr *ipaddr,
					     const u8 sam)
{
	switch (sam) {
	case LOWPAN_IPHC_ADDR_00:
		/* unspec address ::
		 * Do nothing, address is already ::
		 */
		break;
	case LOWPAN_IPHC_ADDR_01:
		/* TODO */
	case LOWPAN_IPHC_ADDR_02:
		/* TODO */
	case LOWPAN_IPHC_ADDR_03:
		/* TODO */
		netdev_warn(skb->dev, "SAM value 0x%x not supported\n", sam);
		return -EINVAL;
	default:
		pr_debug("Invalid sam value: 0x%x\n", sam);
		return -EINVAL;
	}

	raw_dump_inline(NULL,
			"Reconstructed context based ipv6 src addr is",
			ipaddr->s6_addr, 16);

	return 0;
}

/* Uncompress function for multicast destination address,
 * when M bit is set.
 */
static int lowpan_uncompress_multicast_daddr(struct sk_buff *skb,
					     struct in6_addr *ipaddr,
					     const u8 dam)
{
	bool fail;

	switch (dam) {
	case LOWPAN_IPHC_DAM_00:
		/* 00:  128 bits.  The full address
		 * is carried in-line.
		 */
		fail = lowpan_fetch_skb(skb, ipaddr->s6_addr, 16);
		break;
	case LOWPAN_IPHC_DAM_01:
		/* 01:  48 bits.  The address takes
		 * the form ffXX::00XX:XXXX:XXXX.
		 */
		ipaddr->s6_addr[0] = 0xFF;
		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[1], 1);
		fail |= lowpan_fetch_skb(skb, &ipaddr->s6_addr[11], 5);
		break;
	case LOWPAN_IPHC_DAM_10:
		/* 10:  32 bits.  The address takes
		 * the form ffXX::00XX:XXXX.
		 */
		ipaddr->s6_addr[0] = 0xFF;
		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[1], 1);
		fail |= lowpan_fetch_skb(skb, &ipaddr->s6_addr[13], 3);
		break;
	case LOWPAN_IPHC_DAM_11:
		/* 11:  8 bits.  The address takes
		 * the form ff02::00XX.
		 */
		ipaddr->s6_addr[0] = 0xFF;
		ipaddr->s6_addr[1] = 0x02;
		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[15], 1);
		break;
	default:
		pr_debug("DAM value has a wrong value: 0x%x\n", dam);
		return -EINVAL;
	}

	if (fail) {
		pr_debug("Failed to fetch skb data\n");
		return -EIO;
	}

	raw_dump_inline(NULL, "Reconstructed ipv6 multicast addr is",
			ipaddr->s6_addr, 16);

	return 0;
}

/* TTL uncompression values */
static const u8 lowpan_ttl_values[] = { 0, 1, 64, 255 };

int
lowpan_header_decompress(struct sk_buff *skb, struct net_device *dev,
			 const u8 *saddr, const u8 saddr_type,
			 const u8 saddr_len, const u8 *daddr,
			 const u8 daddr_type, const u8 daddr_len,
			 u8 iphc0, u8 iphc1)
{
	struct ipv6hdr hdr = {};
	u8 tmp, num_context = 0;
	int err;

	raw_dump_table(__func__, "raw skb data dump uncompressed",
		       skb->data, skb->len);

	/* another if the CID flag is set */
	if (iphc1 & LOWPAN_IPHC_CID) {
		pr_debug("CID flag is set, increase header with one\n");
		if (lowpan_fetch_skb(skb, &num_context, sizeof(num_context)))
			return -EINVAL;
	}

	hdr.version = 6;

	/* Traffic Class and Flow Label */
	switch ((iphc0 & LOWPAN_IPHC_TF) >> 3) {
	/* Traffic Class and FLow Label carried in-line
	 * ECN + DSCP + 4-bit Pad + Flow Label (4 bytes)
	 */
	case 0: /* 00b */
		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))
			return -EINVAL;

		memcpy(&hdr.flow_lbl, &skb->data[0], 3);
		skb_pull(skb, 3);
		hdr.priority = ((tmp >> 2) & 0x0f);
		hdr.flow_lbl[0] = ((tmp >> 2) & 0x30) | (tmp << 6) |
					(hdr.flow_lbl[0] & 0x0f);
		break;
	/* Traffic class carried in-line
	 * ECN + DSCP (1 byte), Flow Label is elided
	 */
	case 2: /* 10b */
		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))
			return -EINVAL;

		hdr.priority = ((tmp >> 2) & 0x0f);
		hdr.flow_lbl[0] = ((tmp << 6) & 0xC0) | ((tmp >> 2) & 0x30);
		break;
	/* Flow Label carried in-line
	 * ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided
	 */
	case 1: /* 01b */
		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))
			return -EINVAL;

		hdr.flow_lbl[0] = (tmp & 0x0F) | ((tmp >> 2) & 0x30);
		memcpy(&hdr.flow_lbl[1], &skb->data[0], 2);
		skb_pull(skb, 2);
		break;
	/* Traffic Class and Flow Label are elided */
	case 3: /* 11b */
		break;
	default:
		break;
	}

	/* Next Header */
	if ((iphc0 & LOWPAN_IPHC_NH_C) == 0) {
		/* Next header is carried inline */
		if (lowpan_fetch_skb(skb, &hdr.nexthdr, sizeof(hdr.nexthdr)))
			return -EINVAL;

		pr_debug("NH flag is set, next header carried inline: %02x\n",
			 hdr.nexthdr);
	}

	/* Hop Limit */
	if ((iphc0 & 0x03) != LOWPAN_IPHC_TTL_I) {
		hdr.hop_limit = lowpan_ttl_values[iphc0 & 0x03];
	} else {
		if (lowpan_fetch_skb(skb, &hdr.hop_limit,
				     sizeof(hdr.hop_limit)))
			return -EINVAL;
	}

	/* Extract SAM to the tmp variable */
	tmp = ((iphc1 & LOWPAN_IPHC_SAM) >> LOWPAN_IPHC_SAM_BIT) & 0x03;

	if (iphc1 & LOWPAN_IPHC_SAC) {
		/* Source address context based uncompression */
		pr_debug("SAC bit is set. Handle context based source address.\n");
		err = uncompress_context_based_src_addr(skb, &hdr.saddr, tmp);
	} else {
		/* Source address uncompression */
		pr_debug("source address stateless compression\n");
		err = uncompress_addr(skb, &hdr.saddr, tmp, saddr,
				      saddr_type, saddr_len);
	}

	/* Check on error of previous branch */
	if (err)
		return -EINVAL;

	/* Extract DAM to the tmp variable */
	tmp = ((iphc1 & LOWPAN_IPHC_DAM_11) >> LOWPAN_IPHC_DAM_BIT) & 0x03;

	/* check for Multicast Compression */
	if (iphc1 & LOWPAN_IPHC_M) {
		if (iphc1 & LOWPAN_IPHC_DAC) {
			pr_debug("dest: context-based mcast compression\n");
			/* TODO: implement this */
		} else {
			err = lowpan_uncompress_multicast_daddr(skb, &hdr.daddr,
								tmp);

			if (err)
				return -EINVAL;
		}
	} else {
		err = uncompress_addr(skb, &hdr.daddr, tmp, daddr,
				      daddr_type, daddr_len);
		pr_debug("dest: stateless compression mode %d dest %pI6c\n",
			 tmp, &hdr.daddr);
		if (err)
			return -EINVAL;
	}

	/* Next header data uncompression */
	if (iphc0 & LOWPAN_IPHC_NH_C) {
		err = lowpan_nhc_do_uncompression(skb, dev, &hdr);
		if (err < 0)
			return err;
	} else {
		err = skb_cow(skb, sizeof(hdr));
		if (unlikely(err))
			return err;
	}

	switch (lowpan_priv(dev)->lltype) {
	case LOWPAN_LLTYPE_IEEE802154:
		if (lowpan_802154_cb(skb)->d_size)
			hdr.payload_len = htons(lowpan_802154_cb(skb)->d_size -
						sizeof(struct ipv6hdr));
		else
			hdr.payload_len = htons(skb->len);
		break;
	default:
		hdr.payload_len = htons(skb->len);
		break;
	}

	pr_debug("skb headroom size = %d, data length = %d\n",
		 skb_headroom(skb), skb->len);

	pr_debug("IPv6 header dump:\n\tversion = %d\n\tlength  = %d\n\t"
		 "nexthdr = 0x%02x\n\thop_lim = %d\n\tdest    = %pI6c\n",
		hdr.version, ntohs(hdr.payload_len), hdr.nexthdr,
		hdr.hop_limit, &hdr.daddr);

	skb_push(skb, sizeof(hdr));
	skb_reset_network_header(skb);
	skb_copy_to_linear_data(skb, &hdr, sizeof(hdr));

	raw_dump_table(__func__, "raw header dump", (u8 *)&hdr, sizeof(hdr));

	return 0;
}
EXPORT_SYMBOL_GPL(lowpan_header_decompress);

static u8 lowpan_compress_addr_64(u8 **hc_ptr, u8 shift,
				  const struct in6_addr *ipaddr,
				  const unsigned char *lladdr)
{
	u8 val = 0;

	if (is_addr_mac_addr_based(ipaddr, lladdr)) {
		val = 3; /* 0-bits */
		pr_debug("address compression 0 bits\n");
	} else if (lowpan_is_iid_16_bit_compressable(ipaddr)) {
		/* compress IID to 16 bits xxxx::XXXX */
		lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr16[7], 2);
		val = 2; /* 16-bits */
		raw_dump_inline(NULL, "Compressed ipv6 addr is (16 bits)",
				*hc_ptr - 2, 2);
	} else {
		/* do not compress IID => xxxx::IID */
		lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr16[4], 8);
		val = 1; /* 64-bits */
		raw_dump_inline(NULL, "Compressed ipv6 addr is (64 bits)",
				*hc_ptr - 8, 8);
	}

	return rol8(val, shift);
}

int lowpan_header_compress(struct sk_buff *skb, struct net_device *dev,
			   unsigned short type, const void *_daddr,
			   const void *_saddr, unsigned int len)
{
	u8 tmp, iphc0, iphc1, *hc_ptr;
	struct ipv6hdr *hdr;
	u8 head[LOWPAN_IPHC_MAX_HC_BUF_LEN] = {};
	int ret, addr_type;

	if (type != ETH_P_IPV6)
		return -EINVAL;

	hdr = ipv6_hdr(skb);
	hc_ptr = head + 2;

	pr_debug("IPv6 header dump:\n\tversion = %d\n\tlength  = %d\n"
		 "\tnexthdr = 0x%02x\n\thop_lim = %d\n\tdest    = %pI6c\n",
		 hdr->version, ntohs(hdr->payload_len), hdr->nexthdr,
		 hdr->hop_limit, &hdr->daddr);

	raw_dump_table(__func__, "raw skb network header dump",
		       skb_network_header(skb), sizeof(struct ipv6hdr));

	/* As we copy some bit-length fields, in the IPHC encoding bytes,
	 * we sometimes use |=
	 * If the field is 0, and the current bit value in memory is 1,
	 * this does not work. We therefore reset the IPHC encoding here
	 */
	iphc0 = LOWPAN_DISPATCH_IPHC;
	iphc1 = 0;

	/* TODO: context lookup */

	raw_dump_inline(__func__, "saddr",
			(unsigned char *)_saddr, IEEE802154_ADDR_LEN);
	raw_dump_inline(__func__, "daddr",
			(unsigned char *)_daddr, IEEE802154_ADDR_LEN);

	raw_dump_table(__func__, "sending raw skb network uncompressed packet",
		       skb->data, skb->len);

	/* Traffic class, flow label
	 * If flow label is 0, compress it. If traffic class is 0, compress it
	 * We have to process both in the same time as the offset of traffic
	 * class depends on the presence of version and flow label
	 */

	/* hc format of TC is ECN | DSCP , original one is DSCP | ECN */
	tmp = (hdr->priority << 4) | (hdr->flow_lbl[0] >> 4);
	tmp = ((tmp & 0x03) << 6) | (tmp >> 2);

	if (((hdr->flow_lbl[0] & 0x0F) == 0) &&
	    (hdr->flow_lbl[1] == 0) && (hdr->flow_lbl[2] == 0)) {
		/* flow label can be compressed */
		iphc0 |= LOWPAN_IPHC_FL_C;
		if ((hdr->priority == 0) &&
		    ((hdr->flow_lbl[0] & 0xF0) == 0)) {
			/* compress (elide) all */
			iphc0 |= LOWPAN_IPHC_TC_C;
		} else {
			/* compress only the flow label */
			*hc_ptr = tmp;
			hc_ptr += 1;
		}
	} else {
		/* Flow label cannot be compressed */
		if ((hdr->priority == 0) &&
		    ((hdr->flow_lbl[0] & 0xF0) == 0)) {
			/* compress only traffic class */
			iphc0 |= LOWPAN_IPHC_TC_C;
			*hc_ptr = (tmp & 0xc0) | (hdr->flow_lbl[0] & 0x0F);
			memcpy(hc_ptr + 1, &hdr->flow_lbl[1], 2);
			hc_ptr += 3;
		} else {
			/* compress nothing */
			memcpy(hc_ptr, hdr, 4);
			/* replace the top byte with new ECN | DSCP format */
			*hc_ptr = tmp;
			hc_ptr += 4;
		}
	}

	/* NOTE: payload length is always compressed */

	/* Check if we provide the nhc format for nexthdr and compression
	 * functionality. If not nexthdr is handled inline and not compressed.
	 */
	ret = lowpan_nhc_check_compression(skb, hdr, &hc_ptr, &iphc0);
	if (ret < 0)
		return ret;

	/* Hop limit
	 * if 1:   compress, encoding is 01
	 * if 64:  compress, encoding is 10
	 * if 255: compress, encoding is 11
	 * else do not compress
	 */
	switch (hdr->hop_limit) {
	case 1:
		iphc0 |= LOWPAN_IPHC_TTL_1;
		break;
	case 64:
		iphc0 |= LOWPAN_IPHC_TTL_64;
		break;
	case 255:
		iphc0 |= LOWPAN_IPHC_TTL_255;
		break;
	default:
		lowpan_push_hc_data(&hc_ptr, &hdr->hop_limit,
				    sizeof(hdr->hop_limit));
	}

	addr_type = ipv6_addr_type(&hdr->saddr);
	/* source address compression */
	if (addr_type == IPV6_ADDR_ANY) {
		pr_debug("source address is unspecified, setting SAC\n");
		iphc1 |= LOWPAN_IPHC_SAC;
	} else {
		if (addr_type & IPV6_ADDR_LINKLOCAL) {
			iphc1 |= lowpan_compress_addr_64(&hc_ptr,
							 LOWPAN_IPHC_SAM_BIT,
							 &hdr->saddr, _saddr);
			pr_debug("source address unicast link-local %pI6c iphc1 0x%02x\n",
				 &hdr->saddr, iphc1);
		} else {
			pr_debug("send the full source address\n");
			lowpan_push_hc_data(&hc_ptr, hdr->saddr.s6_addr, 16);
		}
	}

	addr_type = ipv6_addr_type(&hdr->daddr);
	/* destination address compression */
	if (addr_type & IPV6_ADDR_MULTICAST) {
		pr_debug("destination address is multicast: ");
		iphc1 |= LOWPAN_IPHC_M;
		if (lowpan_is_mcast_addr_compressable8(&hdr->daddr)) {
			pr_debug("compressed to 1 octet\n");
			iphc1 |= LOWPAN_IPHC_DAM_11;
			/* use last byte */
			lowpan_push_hc_data(&hc_ptr,
					    &hdr->daddr.s6_addr[15], 1);
		} else if (lowpan_is_mcast_addr_compressable32(&hdr->daddr)) {
			pr_debug("compressed to 4 octets\n");
			iphc1 |= LOWPAN_IPHC_DAM_10;
			/* second byte + the last three */
			lowpan_push_hc_data(&hc_ptr,
					    &hdr->daddr.s6_addr[1], 1);
			lowpan_push_hc_data(&hc_ptr,
					    &hdr->daddr.s6_addr[13], 3);
		} else if (lowpan_is_mcast_addr_compressable48(&hdr->daddr)) {
			pr_debug("compressed to 6 octets\n");
			iphc1 |= LOWPAN_IPHC_DAM_01;
			/* second byte + the last five */
			lowpan_push_hc_data(&hc_ptr,
					    &hdr->daddr.s6_addr[1], 1);
			lowpan_push_hc_data(&hc_ptr,
					    &hdr->daddr.s6_addr[11], 5);
		} else {
			pr_debug("using full address\n");
			iphc1 |= LOWPAN_IPHC_DAM_00;
			lowpan_push_hc_data(&hc_ptr, hdr->daddr.s6_addr, 16);
		}
	} else {
		if (addr_type & IPV6_ADDR_LINKLOCAL) {
			/* TODO: context lookup */
			iphc1 |= lowpan_compress_addr_64(&hc_ptr,
				LOWPAN_IPHC_DAM_BIT, &hdr->daddr, _daddr);
			pr_debug("dest address unicast link-local %pI6c "
				 "iphc1 0x%02x\n", &hdr->daddr, iphc1);
		} else {
			pr_debug("dest address unicast %pI6c\n", &hdr->daddr);
			lowpan_push_hc_data(&hc_ptr, hdr->daddr.s6_addr, 16);
		}
	}

	/* next header compression */
	if (iphc0 & LOWPAN_IPHC_NH_C) {
		ret = lowpan_nhc_do_compression(skb, hdr, &hc_ptr);
		if (ret < 0)
			return ret;
	}

	head[0] = iphc0;
	head[1] = iphc1;

	skb_pull(skb, sizeof(struct ipv6hdr));
	skb_reset_transport_header(skb);
	memcpy(skb_push(skb, hc_ptr - head), head, hc_ptr - head);
	skb_reset_network_header(skb);

	pr_debug("header len %d skb %u\n", (int)(hc_ptr - head), skb->len);

	raw_dump_table(__func__, "raw skb data dump compressed",
		       skb->data, skb->len);
	return 0;
}
EXPORT_SYMBOL_GPL(lowpan_header_compress);