Linux 4.6-rc6

[linux/fpc-iii.git] / net / 6lowpan / iphc.c

/*
 * 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>

/* special link-layer handling */
#include <net/mac802154.h>

#include "6lowpan_i.h"
#include "nhc.h"

/* Values of fields within the IPHC encoding first byte */
#define LOWPAN_IPHC_TF_MASK     0x18
#define LOWPAN_IPHC_TF_00       0x00
#define LOWPAN_IPHC_TF_01       0x08
#define LOWPAN_IPHC_TF_10       0x10
#define LOWPAN_IPHC_TF_11       0x18

#define LOWPAN_IPHC_NH          0x04

#define LOWPAN_IPHC_HLIM_MASK   0x03
#define LOWPAN_IPHC_HLIM_00     0x00
#define LOWPAN_IPHC_HLIM_01     0x01
#define LOWPAN_IPHC_HLIM_10     0x02
#define LOWPAN_IPHC_HLIM_11     0x03

/* Values of fields within the IPHC encoding second byte */
#define LOWPAN_IPHC_CID         0x80

#define LOWPAN_IPHC_SAC         0x40

#define LOWPAN_IPHC_SAM_MASK    0x30
#define LOWPAN_IPHC_SAM_00      0x00
#define LOWPAN_IPHC_SAM_01      0x10
#define LOWPAN_IPHC_SAM_10      0x20
#define LOWPAN_IPHC_SAM_11      0x30

#define LOWPAN_IPHC_M           0x08

#define LOWPAN_IPHC_DAC         0x04

#define LOWPAN_IPHC_DAM_MASK    0x03
#define LOWPAN_IPHC_DAM_00      0x00
#define LOWPAN_IPHC_DAM_01      0x01
#define LOWPAN_IPHC_DAM_10      0x02
#define LOWPAN_IPHC_DAM_11      0x03

/* ipv6 address based on mac
 * second bit-flip (Universe/Local) is done according RFC2464
 */
#define is_addr_mac_addr_based(a, m) \
        ((((a)->s6_addr[8])  == (((m)[0]) ^ 0x02)) &&   \
         (((a)->s6_addr[9])  == (m)[1]) &&              \
         (((a)->s6_addr[10]) == (m)[2]) &&              \
         (((a)->s6_addr[11]) == (m)[3]) &&              \
         (((a)->s6_addr[12]) == (m)[4]) &&              \
         (((a)->s6_addr[13]) == (m)[5]) &&              \
         (((a)->s6_addr[14]) == (m)[6]) &&              \
         (((a)->s6_addr[15]) == (m)[7]))

/* check whether we can compress the IID to 16 bits,
 * it's possible for unicast addresses with first 49 bits are zero only.
 */
#define lowpan_is_iid_16_bit_compressable(a)    \
        ((((a)->s6_addr16[4]) == 0) &&          \
         (((a)->s6_addr[10]) == 0) &&           \
         (((a)->s6_addr[11]) == 0xff) &&        \
         (((a)->s6_addr[12]) == 0xfe) &&        \
         (((a)->s6_addr[13]) == 0))

/* check whether the 112-bit gid of the multicast address is mappable to: */

/* 48 bits, FFXX::00XX:XXXX:XXXX */
#define lowpan_is_mcast_addr_compressable48(a)  \
        ((((a)->s6_addr16[1]) == 0) &&          \
         (((a)->s6_addr16[2]) == 0) &&          \
         (((a)->s6_addr16[3]) == 0) &&          \
         (((a)->s6_addr16[4]) == 0) &&          \
         (((a)->s6_addr[10]) == 0))

/* 32 bits, FFXX::00XX:XXXX */
#define lowpan_is_mcast_addr_compressable32(a)  \
        ((((a)->s6_addr16[1]) == 0) &&          \
         (((a)->s6_addr16[2]) == 0) &&          \
         (((a)->s6_addr16[3]) == 0) &&          \
         (((a)->s6_addr16[4]) == 0) &&          \
         (((a)->s6_addr16[5]) == 0) &&          \
         (((a)->s6_addr[12]) == 0))

/* 8 bits, FF02::00XX */
#define lowpan_is_mcast_addr_compressable8(a)   \
        ((((a)->s6_addr[1])  == 2) &&           \
         (((a)->s6_addr16[1]) == 0) &&          \
         (((a)->s6_addr16[2]) == 0) &&          \
         (((a)->s6_addr16[3]) == 0) &&          \
         (((a)->s6_addr16[4]) == 0) &&          \
         (((a)->s6_addr16[5]) == 0) &&          \
         (((a)->s6_addr16[6]) == 0) &&          \
         (((a)->s6_addr[14]) == 0))

#define LOWPAN_IPHC_CID_DCI(cid)        (cid & 0x0f)
#define LOWPAN_IPHC_CID_SCI(cid)        ((cid & 0xf0) >> 4)

static inline void iphc_uncompress_eui64_lladdr(struct in6_addr *ipaddr,
                                                const void *lladdr)
{
        /* fe:80::XXXX:XXXX:XXXX:XXXX
         *        \_________________/
         *              hwaddr
         */
        ipaddr->s6_addr[0] = 0xFE;
        ipaddr->s6_addr[1] = 0x80;
        memcpy(&ipaddr->s6_addr[8], lladdr, EUI64_ADDR_LEN);
        /* second bit-flip (Universe/Local)
         * is done according RFC2464
         */
        ipaddr->s6_addr[8] ^= 0x02;
}

static inline void iphc_uncompress_802154_lladdr(struct in6_addr *ipaddr,
                                                 const void *lladdr)
{
        const struct ieee802154_addr *addr = lladdr;
        u8 eui64[EUI64_ADDR_LEN] = { };

        switch (addr->mode) {
        case IEEE802154_ADDR_LONG:
                ieee802154_le64_to_be64(eui64, &addr->extended_addr);
                iphc_uncompress_eui64_lladdr(ipaddr, eui64);
                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;
                ieee802154_le16_to_be16(&ipaddr->s6_addr16[7],
                                        &addr->short_addr);
                break;
        default:
                /* should never handled and filtered by 802154 6lowpan */
                WARN_ON_ONCE(1);
                break;
        }
}

static struct lowpan_iphc_ctx *
lowpan_iphc_ctx_get_by_id(const struct net_device *dev, u8 id)
{
        struct lowpan_iphc_ctx *ret = &lowpan_priv(dev)->ctx.table[id];

        if (!lowpan_iphc_ctx_is_active(ret))
                return NULL;

        return ret;
}

static struct lowpan_iphc_ctx *
lowpan_iphc_ctx_get_by_addr(const struct net_device *dev,
                            const struct in6_addr *addr)
{
        struct lowpan_iphc_ctx *table = lowpan_priv(dev)->ctx.table;
        struct lowpan_iphc_ctx *ret = NULL;
        struct in6_addr addr_pfx;
        u8 addr_plen;
        int i;

        for (i = 0; i < LOWPAN_IPHC_CTX_TABLE_SIZE; i++) {
                /* Check if context is valid. A context that is not valid
                 * MUST NOT be used for compression.
                 */
                if (!lowpan_iphc_ctx_is_active(&table[i]) ||
                    !lowpan_iphc_ctx_is_compression(&table[i]))
                        continue;

                ipv6_addr_prefix(&addr_pfx, addr, table[i].plen);

                /* if prefix len < 64, the remaining bits until 64th bit is
                 * zero. Otherwise we use table[i]->plen.
                 */
                if (table[i].plen < 64)
                        addr_plen = 64;
                else
                        addr_plen = table[i].plen;

                if (ipv6_prefix_equal(&addr_pfx, &table[i].pfx, addr_plen)) {
                        /* remember first match */
                        if (!ret) {
                                ret = &table[i];
                                continue;
                        }

                        /* get the context with longest prefix len */
                        if (table[i].plen > ret->plen)
                                ret = &table[i];
                }
        }

        return ret;
}

static struct lowpan_iphc_ctx *
lowpan_iphc_ctx_get_by_mcast_addr(const struct net_device *dev,
                                  const struct in6_addr *addr)
{
        struct lowpan_iphc_ctx *table = lowpan_priv(dev)->ctx.table;
        struct lowpan_iphc_ctx *ret = NULL;
        struct in6_addr addr_mcast, network_pfx = {};
        int i;

        /* init mcast address with  */
        memcpy(&addr_mcast, addr, sizeof(*addr));

        for (i = 0; i < LOWPAN_IPHC_CTX_TABLE_SIZE; i++) {
                /* Check if context is valid. A context that is not valid
                 * MUST NOT be used for compression.
                 */
                if (!lowpan_iphc_ctx_is_active(&table[i]) ||
                    !lowpan_iphc_ctx_is_compression(&table[i]))
                        continue;

                /* setting plen */
                addr_mcast.s6_addr[3] = table[i].plen;
                /* get network prefix to copy into multicast address */
                ipv6_addr_prefix(&network_pfx, &table[i].pfx,
                                 table[i].plen);
                /* setting network prefix */
                memcpy(&addr_mcast.s6_addr[4], &network_pfx, 8);

                if (ipv6_addr_equal(addr, &addr_mcast)) {
                        ret = &table[i];
                        break;
                }
        }

        return ret;
}

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

        switch (address_mode) {
        /* SAM and DAM are the same here */
        case LOWPAN_IPHC_DAM_00:
                /* for global link addresses */
                fail = lowpan_fetch_skb(skb, ipaddr->s6_addr, 16);
                break;
        case LOWPAN_IPHC_SAM_01:
        case LOWPAN_IPHC_DAM_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_SAM_10:
        case LOWPAN_IPHC_DAM_10:
                /* 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_SAM_11:
        case LOWPAN_IPHC_DAM_11:
                fail = false;
                switch (lowpan_priv(dev)->lltype) {
                case LOWPAN_LLTYPE_IEEE802154:
                        iphc_uncompress_802154_lladdr(ipaddr, lladdr);
                        break;
                default:
                        iphc_uncompress_eui64_lladdr(ipaddr, lladdr);
                        break;
                }
                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_ctx_addr(struct sk_buff *skb,
                               const struct net_device *dev,
                               const struct lowpan_iphc_ctx *ctx,
                               struct in6_addr *ipaddr, u8 address_mode,
                               const void *lladdr)
{
        bool fail;

        switch (address_mode) {
        /* SAM and DAM are the same here */
        case LOWPAN_IPHC_DAM_00:
                fail = false;
                /* SAM_00 -> unspec address ::
                 * Do nothing, address is already ::
                 *
                 * DAM 00 -> reserved should never occur.
                 */
                break;
        case LOWPAN_IPHC_SAM_01:
        case LOWPAN_IPHC_DAM_01:
                fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[8], 8);
                ipv6_addr_prefix_copy(ipaddr, &ctx->pfx, ctx->plen);
                break;
        case LOWPAN_IPHC_SAM_10:
        case LOWPAN_IPHC_DAM_10:
                ipaddr->s6_addr[11] = 0xFF;
                ipaddr->s6_addr[12] = 0xFE;
                fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[14], 2);
                ipv6_addr_prefix_copy(ipaddr, &ctx->pfx, ctx->plen);
                break;
        case LOWPAN_IPHC_SAM_11:
        case LOWPAN_IPHC_DAM_11:
                fail = false;
                switch (lowpan_priv(dev)->lltype) {
                case LOWPAN_LLTYPE_IEEE802154:
                        iphc_uncompress_802154_lladdr(ipaddr, lladdr);
                        break;
                default:
                        iphc_uncompress_eui64_lladdr(ipaddr, lladdr);
                        break;
                }
                ipv6_addr_prefix_copy(ipaddr, &ctx->pfx, ctx->plen);
                break;
        default:
                pr_debug("Invalid sam 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 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,
                                             u8 address_mode)
{
        bool fail;

        switch (address_mode) {
        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", address_mode);
                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;
}

static int lowpan_uncompress_multicast_ctx_daddr(struct sk_buff *skb,
                                                 struct lowpan_iphc_ctx *ctx,
                                                 struct in6_addr *ipaddr,
                                                 u8 address_mode)
{
        struct in6_addr network_pfx = {};
        bool fail;

        ipaddr->s6_addr[0] = 0xFF;
        fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[1], 2);
        fail |= lowpan_fetch_skb(skb, &ipaddr->s6_addr[12], 4);
        if (fail)
                return -EIO;

        /* take prefix_len and network prefix from the context */
        ipaddr->s6_addr[3] = ctx->plen;
        /* get network prefix to copy into multicast address */
        ipv6_addr_prefix(&network_pfx, &ctx->pfx, ctx->plen);
        /* setting network prefix */
        memcpy(&ipaddr->s6_addr[4], &network_pfx, 8);

        return 0;
}

/* get the ecn values from iphc tf format and set it to ipv6hdr */
static inline void lowpan_iphc_tf_set_ecn(struct ipv6hdr *hdr, const u8 *tf)
{
        /* get the two higher bits which is ecn */
        u8 ecn = tf[0] & 0xc0;

        /* ECN takes 0x30 in hdr->flow_lbl[0] */
        hdr->flow_lbl[0] |= (ecn >> 2);
}

/* get the dscp values from iphc tf format and set it to ipv6hdr */
static inline void lowpan_iphc_tf_set_dscp(struct ipv6hdr *hdr, const u8 *tf)
{
        /* DSCP is at place after ECN */
        u8 dscp = tf[0] & 0x3f;

        /* The four highest bits need to be set at hdr->priority */
        hdr->priority |= ((dscp & 0x3c) >> 2);
        /* The two lower bits is part of hdr->flow_lbl[0] */
        hdr->flow_lbl[0] |= ((dscp & 0x03) << 6);
}

/* get the flow label values from iphc tf format and set it to ipv6hdr */
static inline void lowpan_iphc_tf_set_lbl(struct ipv6hdr *hdr, const u8 *lbl)
{
        /* flow label is always some array started with lower nibble of
         * flow_lbl[0] and followed with two bytes afterwards. Inside inline
         * data the flow_lbl position can be different, which will be handled
         * by lbl pointer. E.g. case "01" vs "00" the traffic class is 8 bit
         * shifted, the different lbl pointer will handle that.
         *
         * The flow label will started at lower nibble of flow_lbl[0], the
         * higher nibbles are part of DSCP + ECN.
         */
        hdr->flow_lbl[0] |= lbl[0] & 0x0f;
        memcpy(&hdr->flow_lbl[1], &lbl[1], 2);
}

/* lowpan_iphc_tf_decompress - decompress the traffic class.
 *      This function will return zero on success, a value lower than zero if
 *      failed.
 */
static int lowpan_iphc_tf_decompress(struct sk_buff *skb, struct ipv6hdr *hdr,
                                     u8 val)
{
        u8 tf[4];

        /* Traffic Class and Flow Label */
        switch (val) {
        case LOWPAN_IPHC_TF_00:
                /* ECN + DSCP + 4-bit Pad + Flow Label (4 bytes) */
                if (lowpan_fetch_skb(skb, tf, 4))
                        return -EINVAL;

                /*                      1                   2                   3
                 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 * |ECN|   DSCP    |  rsv  |             Flow Label                |
                 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 */
                lowpan_iphc_tf_set_ecn(hdr, tf);
                lowpan_iphc_tf_set_dscp(hdr, tf);
                lowpan_iphc_tf_set_lbl(hdr, &tf[1]);
                break;
        case LOWPAN_IPHC_TF_01:
                /* ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided. */
                if (lowpan_fetch_skb(skb, tf, 3))
                        return -EINVAL;

                /*                     1                   2
                 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
                 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 * |ECN|rsv|             Flow Label                |
                 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 */
                lowpan_iphc_tf_set_ecn(hdr, tf);
                lowpan_iphc_tf_set_lbl(hdr, &tf[0]);
                break;
        case LOWPAN_IPHC_TF_10:
                /* ECN + DSCP (1 byte), Flow Label is elided. */
                if (lowpan_fetch_skb(skb, tf, 1))
                        return -EINVAL;

                /*  0 1 2 3 4 5 6 7
                 * +-+-+-+-+-+-+-+-+
                 * |ECN|   DSCP    |
                 * +-+-+-+-+-+-+-+-+
                 */
                lowpan_iphc_tf_set_ecn(hdr, tf);
                lowpan_iphc_tf_set_dscp(hdr, tf);
                break;
        case LOWPAN_IPHC_TF_11:
                /* Traffic Class and Flow Label are elided */
                break;
        default:
                WARN_ON_ONCE(1);
                return -EINVAL;
        }

        return 0;
}

/* TTL uncompression values */
static const u8 lowpan_ttl_values[] = {
        [LOWPAN_IPHC_HLIM_01] = 1,
        [LOWPAN_IPHC_HLIM_10] = 64,
        [LOWPAN_IPHC_HLIM_11] = 255,
};

int lowpan_header_decompress(struct sk_buff *skb, const struct net_device *dev,
                             const void *daddr, const void *saddr)
{
        struct ipv6hdr hdr = {};
        struct lowpan_iphc_ctx *ci;
        u8 iphc0, iphc1, cid = 0;
        int err;

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

        if (lowpan_fetch_skb(skb, &iphc0, sizeof(iphc0)) ||
            lowpan_fetch_skb(skb, &iphc1, sizeof(iphc1)))
                return -EINVAL;

        hdr.version = 6;

        /* default CID = 0, another if the CID flag is set */
        if (iphc1 & LOWPAN_IPHC_CID) {
                if (lowpan_fetch_skb(skb, &cid, sizeof(cid)))
                        return -EINVAL;
        }

        err = lowpan_iphc_tf_decompress(skb, &hdr,
                                        iphc0 & LOWPAN_IPHC_TF_MASK);
        if (err < 0)
                return err;

        /* Next Header */
        if (!(iphc0 & LOWPAN_IPHC_NH)) {
                /* 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 & LOWPAN_IPHC_HLIM_MASK) != LOWPAN_IPHC_HLIM_00) {
                hdr.hop_limit = lowpan_ttl_values[iphc0 & LOWPAN_IPHC_HLIM_MASK];
        } else {
                if (lowpan_fetch_skb(skb, &hdr.hop_limit,
                                     sizeof(hdr.hop_limit)))
                        return -EINVAL;
        }

        if (iphc1 & LOWPAN_IPHC_SAC) {
                spin_lock_bh(&lowpan_priv(dev)->ctx.lock);
                ci = lowpan_iphc_ctx_get_by_id(dev, LOWPAN_IPHC_CID_SCI(cid));
                if (!ci) {
                        spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);
                        return -EINVAL;
                }

                pr_debug("SAC bit is set. Handle context based source address.\n");
                err = uncompress_ctx_addr(skb, dev, ci, &hdr.saddr,
                                          iphc1 & LOWPAN_IPHC_SAM_MASK, saddr);
                spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);
        } else {
                /* Source address uncompression */
                pr_debug("source address stateless compression\n");
                err = uncompress_addr(skb, dev, &hdr.saddr,
                                      iphc1 & LOWPAN_IPHC_SAM_MASK, saddr);
        }

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

        switch (iphc1 & (LOWPAN_IPHC_M | LOWPAN_IPHC_DAC)) {
        case LOWPAN_IPHC_M | LOWPAN_IPHC_DAC:
                spin_lock_bh(&lowpan_priv(dev)->ctx.lock);
                ci = lowpan_iphc_ctx_get_by_id(dev, LOWPAN_IPHC_CID_DCI(cid));
                if (!ci) {
                        spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);
                        return -EINVAL;
                }

                /* multicast with context */
                pr_debug("dest: context-based mcast compression\n");
                err = lowpan_uncompress_multicast_ctx_daddr(skb, ci,
                                                            &hdr.daddr,
                                                            iphc1 & LOWPAN_IPHC_DAM_MASK);
                spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);
                break;
        case LOWPAN_IPHC_M:
                /* multicast */
                err = lowpan_uncompress_multicast_daddr(skb, &hdr.daddr,
                                                        iphc1 & LOWPAN_IPHC_DAM_MASK);
                break;
        case LOWPAN_IPHC_DAC:
                spin_lock_bh(&lowpan_priv(dev)->ctx.lock);
                ci = lowpan_iphc_ctx_get_by_id(dev, LOWPAN_IPHC_CID_DCI(cid));
                if (!ci) {
                        spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);
                        return -EINVAL;
                }

                /* Destination address context based uncompression */
                pr_debug("DAC bit is set. Handle context based destination address.\n");
                err = uncompress_ctx_addr(skb, dev, ci, &hdr.daddr,
                                          iphc1 & LOWPAN_IPHC_DAM_MASK, daddr);
                spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);
                break;
        default:
                err = uncompress_addr(skb, dev, &hdr.daddr,
                                      iphc1 & LOWPAN_IPHC_DAM_MASK, daddr);
                pr_debug("dest: stateless compression mode %d dest %pI6c\n",
                         iphc1 & LOWPAN_IPHC_DAM_MASK, &hdr.daddr);
                break;
        }

        if (err)
                return -EINVAL;

        /* Next header data uncompression */
        if (iphc0 & LOWPAN_IPHC_NH) {
                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 const u8 lowpan_iphc_dam_to_sam_value[] = {
        [LOWPAN_IPHC_DAM_00] = LOWPAN_IPHC_SAM_00,
        [LOWPAN_IPHC_DAM_01] = LOWPAN_IPHC_SAM_01,
        [LOWPAN_IPHC_DAM_10] = LOWPAN_IPHC_SAM_10,
        [LOWPAN_IPHC_DAM_11] = LOWPAN_IPHC_SAM_11,
};

static u8 lowpan_compress_ctx_addr(u8 **hc_ptr, const struct in6_addr *ipaddr,
                                   const struct lowpan_iphc_ctx *ctx,
                                   const unsigned char *lladdr, bool sam)
{
        struct in6_addr tmp = {};
        u8 dam;

        /* check for SAM/DAM = 11 */
        memcpy(&tmp.s6_addr[8], lladdr, 8);
        /* second bit-flip (Universe/Local) is done according RFC2464 */
        tmp.s6_addr[8] ^= 0x02;
        /* context information are always used */
        ipv6_addr_prefix_copy(&tmp, &ctx->pfx, ctx->plen);
        if (ipv6_addr_equal(&tmp, ipaddr)) {
                dam = LOWPAN_IPHC_DAM_11;
                goto out;
        }

        memset(&tmp, 0, sizeof(tmp));
        /* check for SAM/DAM = 10 */
        tmp.s6_addr[11] = 0xFF;
        tmp.s6_addr[12] = 0xFE;
        memcpy(&tmp.s6_addr[14], &ipaddr->s6_addr[14], 2);
        /* context information are always used */
        ipv6_addr_prefix_copy(&tmp, &ctx->pfx, ctx->plen);
        if (ipv6_addr_equal(&tmp, ipaddr)) {
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[14], 2);
                dam = LOWPAN_IPHC_DAM_10;
                goto out;
        }

        memset(&tmp, 0, sizeof(tmp));
        /* check for SAM/DAM = 01, should always match */
        memcpy(&tmp.s6_addr[8], &ipaddr->s6_addr[8], 8);
        /* context information are always used */
        ipv6_addr_prefix_copy(&tmp, &ctx->pfx, ctx->plen);
        if (ipv6_addr_equal(&tmp, ipaddr)) {
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[8], 8);
                dam = LOWPAN_IPHC_DAM_01;
                goto out;
        }

        WARN_ONCE(1, "context found but no address mode matched\n");
        return LOWPAN_IPHC_DAM_00;
out:

        if (sam)
                return lowpan_iphc_dam_to_sam_value[dam];
        else
                return dam;
}

static u8 lowpan_compress_addr_64(u8 **hc_ptr, const struct in6_addr *ipaddr,
                                  const unsigned char *lladdr, bool sam)
{
        u8 dam = LOWPAN_IPHC_DAM_00;

        if (is_addr_mac_addr_based(ipaddr, lladdr)) {
                dam = LOWPAN_IPHC_DAM_11; /* 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);
                dam = LOWPAN_IPHC_DAM_10; /* 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);
                dam = LOWPAN_IPHC_DAM_01; /* 64-bits */
                raw_dump_inline(NULL, "Compressed ipv6 addr is (64 bits)",
                                *hc_ptr - 8, 8);
        }

        if (sam)
                return lowpan_iphc_dam_to_sam_value[dam];
        else
                return dam;
}

/* lowpan_iphc_get_tc - get the ECN + DCSP fields in hc format */
static inline u8 lowpan_iphc_get_tc(const struct ipv6hdr *hdr)
{
        u8 dscp, ecn;

        /* hdr->priority contains the higher bits of dscp, lower are part of
         * flow_lbl[0]. Note ECN, DCSP is swapped in ipv6 hdr.
         */
        dscp = (hdr->priority << 2) | ((hdr->flow_lbl[0] & 0xc0) >> 6);
        /* ECN is at the two lower bits from first nibble of flow_lbl[0] */
        ecn = (hdr->flow_lbl[0] & 0x30);
        /* for pretty debug output, also shift ecn to get the ecn value */
        pr_debug("ecn 0x%02x dscp 0x%02x\n", ecn >> 4, dscp);
        /* ECN is at 0x30 now, shift it to have ECN + DCSP */
        return (ecn << 2) | dscp;
}

/* lowpan_iphc_is_flow_lbl_zero - check if flow label is zero */
static inline bool lowpan_iphc_is_flow_lbl_zero(const struct ipv6hdr *hdr)
{
        return ((!(hdr->flow_lbl[0] & 0x0f)) &&
                !hdr->flow_lbl[1] && !hdr->flow_lbl[2]);
}

/* lowpan_iphc_tf_compress - compress the traffic class which is set by
 *      ipv6hdr. Return the corresponding format identifier which is used.
 */
static u8 lowpan_iphc_tf_compress(u8 **hc_ptr, const struct ipv6hdr *hdr)
{
        /* get ecn dscp data in a byteformat as: ECN(hi) + DSCP(lo) */
        u8 tc = lowpan_iphc_get_tc(hdr), tf[4], val;

        /* printout the traffic class in hc format */
        pr_debug("tc 0x%02x\n", tc);

        if (lowpan_iphc_is_flow_lbl_zero(hdr)) {
                if (!tc) {
                        /* 11:  Traffic Class and Flow Label are elided. */
                        val = LOWPAN_IPHC_TF_11;
                } else {
                        /* 10:  ECN + DSCP (1 byte), Flow Label is elided.
                         *
                         *  0 1 2 3 4 5 6 7
                         * +-+-+-+-+-+-+-+-+
                         * |ECN|   DSCP    |
                         * +-+-+-+-+-+-+-+-+
                         */
                        lowpan_push_hc_data(hc_ptr, &tc, sizeof(tc));
                        val = LOWPAN_IPHC_TF_10;
                }
        } else {
                /* check if dscp is zero, it's after the first two bit */
                if (!(tc & 0x3f)) {
                        /* 01:  ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided
                         *
                         *                     1                   2
                         * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
                         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         * |ECN|rsv|             Flow Label                |
                         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         */
                        memcpy(&tf[0], &hdr->flow_lbl[0], 3);
                        /* zero the highest 4-bits, contains DCSP + ECN */
                        tf[0] &= ~0xf0;
                        /* set ECN */
                        tf[0] |= (tc & 0xc0);

                        lowpan_push_hc_data(hc_ptr, tf, 3);
                        val = LOWPAN_IPHC_TF_01;
                } else {
                        /* 00:  ECN + DSCP + 4-bit Pad + Flow Label (4 bytes)
                         *
                         *                      1                   2                   3
                         *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         * |ECN|   DSCP    |  rsv  |             Flow Label                |
                         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         */
                        memcpy(&tf[0], &tc, sizeof(tc));
                        /* highest nibble of flow_lbl[0] is part of DSCP + ECN
                         * which will be the 4-bit pad and will be filled with
                         * zeros afterwards.
                         */
                        memcpy(&tf[1], &hdr->flow_lbl[0], 3);
                        /* zero the 4-bit pad, which is reserved */
                        tf[1] &= ~0xf0;

                        lowpan_push_hc_data(hc_ptr, tf, 4);
                        val = LOWPAN_IPHC_TF_00;
                }
        }

        return val;
}

static u8 lowpan_iphc_mcast_ctx_addr_compress(u8 **hc_ptr,
                                              const struct lowpan_iphc_ctx *ctx,
                                              const struct in6_addr *ipaddr)
{
        u8 data[6];

        /* flags/scope, reserved (RIID) */
        memcpy(data, &ipaddr->s6_addr[1], 2);
        /* group ID */
        memcpy(&data[1], &ipaddr->s6_addr[11], 4);
        lowpan_push_hc_data(hc_ptr, data, 6);

        return LOWPAN_IPHC_DAM_00;
}

static u8 lowpan_iphc_mcast_addr_compress(u8 **hc_ptr,
                                          const struct in6_addr *ipaddr)
{
        u8 val;

        if (lowpan_is_mcast_addr_compressable8(ipaddr)) {
                pr_debug("compressed to 1 octet\n");
                /* use last byte */
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[15], 1);
                val = LOWPAN_IPHC_DAM_11;
        } else if (lowpan_is_mcast_addr_compressable32(ipaddr)) {
                pr_debug("compressed to 4 octets\n");
                /* second byte + the last three */
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[1], 1);
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[13], 3);
                val = LOWPAN_IPHC_DAM_10;
        } else if (lowpan_is_mcast_addr_compressable48(ipaddr)) {
                pr_debug("compressed to 6 octets\n");
                /* second byte + the last five */
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[1], 1);
                lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[11], 5);
                val = LOWPAN_IPHC_DAM_01;
        } else {
                pr_debug("using full address\n");
                lowpan_push_hc_data(hc_ptr, ipaddr->s6_addr, 16);
                val = LOWPAN_IPHC_DAM_00;
        }

        return val;
}

int lowpan_header_compress(struct sk_buff *skb, const struct net_device *dev,
                           const void *daddr, const void *saddr)
{
        u8 iphc0, iphc1, *hc_ptr, cid = 0;
        struct ipv6hdr *hdr;
        u8 head[LOWPAN_IPHC_MAX_HC_BUF_LEN] = {};
        struct lowpan_iphc_ctx *dci, *sci, dci_entry, sci_entry;
        int ret, ipv6_daddr_type, ipv6_saddr_type;

        if (skb->protocol != htons(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;

        raw_dump_inline(__func__, "saddr", saddr, EUI64_ADDR_LEN);
        raw_dump_inline(__func__, "daddr", daddr, EUI64_ADDR_LEN);

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

        ipv6_daddr_type = ipv6_addr_type(&hdr->daddr);
        spin_lock_bh(&lowpan_priv(dev)->ctx.lock);
        if (ipv6_daddr_type & IPV6_ADDR_MULTICAST)
                dci = lowpan_iphc_ctx_get_by_mcast_addr(dev, &hdr->daddr);
        else
                dci = lowpan_iphc_ctx_get_by_addr(dev, &hdr->daddr);
        if (dci) {
                memcpy(&dci_entry, dci, sizeof(*dci));
                cid |= dci->id;
        }
        spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);

        spin_lock_bh(&lowpan_priv(dev)->ctx.lock);
        sci = lowpan_iphc_ctx_get_by_addr(dev, &hdr->saddr);
        if (sci) {
                memcpy(&sci_entry, sci, sizeof(*sci));
                cid |= (sci->id << 4);
        }
        spin_unlock_bh(&lowpan_priv(dev)->ctx.lock);

        /* if cid is zero it will be compressed */
        if (cid) {
                iphc1 |= LOWPAN_IPHC_CID;
                lowpan_push_hc_data(&hc_ptr, &cid, sizeof(cid));
        }

        /* Traffic Class, Flow Label compression */
        iphc0 |= lowpan_iphc_tf_compress(&hc_ptr, hdr);

        /* 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);
        if (ret == -ENOENT)
                lowpan_push_hc_data(&hc_ptr, &hdr->nexthdr,
                                    sizeof(hdr->nexthdr));
        else
                iphc0 |= LOWPAN_IPHC_NH;

        /* 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_HLIM_01;
                break;
        case 64:
                iphc0 |= LOWPAN_IPHC_HLIM_10;
                break;
        case 255:
                iphc0 |= LOWPAN_IPHC_HLIM_11;
                break;
        default:
                lowpan_push_hc_data(&hc_ptr, &hdr->hop_limit,
                                    sizeof(hdr->hop_limit));
        }

        ipv6_saddr_type = ipv6_addr_type(&hdr->saddr);
        /* source address compression */
        if (ipv6_saddr_type == IPV6_ADDR_ANY) {
                pr_debug("source address is unspecified, setting SAC\n");
                iphc1 |= LOWPAN_IPHC_SAC;
        } else {
                if (sci) {
                        iphc1 |= lowpan_compress_ctx_addr(&hc_ptr, &hdr->saddr,
                                                          &sci_entry, saddr,
                                                          true);
                        iphc1 |= LOWPAN_IPHC_SAC;
                } else {
                        if (ipv6_saddr_type & IPV6_ADDR_LINKLOCAL) {
                                iphc1 |= lowpan_compress_addr_64(&hc_ptr,
                                                                 &hdr->saddr,
                                                                 saddr, true);
                                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);
                        }
                }
        }

        /* destination address compression */
        if (ipv6_daddr_type & IPV6_ADDR_MULTICAST) {
                pr_debug("destination address is multicast: ");
                iphc1 |= LOWPAN_IPHC_M;
                if (dci) {
                        iphc1 |= lowpan_iphc_mcast_ctx_addr_compress(&hc_ptr,
                                                                     &dci_entry,
                                                                     &hdr->daddr);
                        iphc1 |= LOWPAN_IPHC_DAC;
                } else {
                        iphc1 |= lowpan_iphc_mcast_addr_compress(&hc_ptr,
                                                                 &hdr->daddr);
                }
        } else {
                if (dci) {
                        iphc1 |= lowpan_compress_ctx_addr(&hc_ptr, &hdr->daddr,
                                                          &dci_entry, daddr,
                                                          false);
                        iphc1 |= LOWPAN_IPHC_DAC;
                } else {
                        if (ipv6_daddr_type & IPV6_ADDR_LINKLOCAL) {
                                iphc1 |= lowpan_compress_addr_64(&hc_ptr,
                                                                 &hdr->daddr,
                                                                 daddr, false);
                                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) {
                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);