/*
 * gw.c - CAN frame Gateway/Router/Bridge with netlink interface
 *
 * Copyright (c) 2011 Volkswagen Group Electronic Research
 * 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 Volkswagen nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * The provided data structures and external interfaces from this code
 * are not restricted to be used by modules with a GPL compatible license.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
 * OWNER 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/module.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/if_arp.h>
#include <linux/skbuff.h>
#include <linux/can.h>
#include <linux/can/core.h>
#include <linux/can/skb.h>
#include <linux/can/gw.h>
#include <net/rtnetlink.h>
#include <net/net_namespace.h>
#include <net/sock.h>

#define CAN_GW_VERSION "20130117"
#define CAN_GW_NAME "can-gw"

MODULE_DESCRIPTION("PF_CAN netlink gateway");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Oliver Hartkopp <oliver.hartkopp@volkswagen.de>");
MODULE_ALIAS(CAN_GW_NAME);

#define CGW_MIN_HOPS 1
#define CGW_MAX_HOPS 6
#define CGW_DEFAULT_HOPS 1

static unsigned int max_hops __read_mostly = CGW_DEFAULT_HOPS;
module_param(max_hops, uint, S_IRUGO);
MODULE_PARM_DESC(max_hops,
                 "maximum " CAN_GW_NAME " routing hops for CAN frames "
                 "(valid values: " __stringify(CGW_MIN_HOPS) "-"
                 __stringify(CGW_MAX_HOPS) " hops, "
                 "default: " __stringify(CGW_DEFAULT_HOPS) ")");

static HLIST_HEAD(cgw_list);
static struct notifier_block notifier;

static struct kmem_cache *cgw_cache __read_mostly;

/* structure that contains the (on-the-fly) CAN frame modifications */
struct cf_mod {
        struct {
                struct can_frame and;
                struct can_frame or;
                struct can_frame xor;
                struct can_frame set;
        } modframe;
        struct {
                u8 and;
                u8 or;
                u8 xor;
                u8 set;
        } modtype;
        void (*modfunc[MAX_MODFUNCTIONS])(struct can_frame *cf,
                                          struct cf_mod *mod);

        /* CAN frame checksum calculation after CAN frame modifications */
        struct {
                struct cgw_csum_xor xor;
                struct cgw_csum_crc8 crc8;
        } csum;
        struct {
                void (*xor)(struct can_frame *cf, struct cgw_csum_xor *xor);
                void (*crc8)(struct can_frame *cf, struct cgw_csum_crc8 *crc8);
        } csumfunc;
};


/*
 * So far we just support CAN -> CAN routing and frame modifications.
 *
 * The internal can_can_gw structure contains data and attributes for
 * a CAN -> CAN gateway job.
 */
struct can_can_gw {
        struct can_filter filter;
        int src_idx;
        int dst_idx;
};

/* list entry for CAN gateways jobs */
struct cgw_job {
        struct hlist_node list;
        struct rcu_head rcu;
        u32 handled_frames;
        u32 dropped_frames;
        u32 deleted_frames;
        struct cf_mod mod;
        union {
                /* CAN frame data source */
                struct net_device *dev;
        } src;
        union {
                /* CAN frame data destination */
                struct net_device *dev;
        } dst;
        union {
                struct can_can_gw ccgw;
                /* tbc */
        };
        u8 gwtype;
        u16 flags;
};

/* modification functions that are invoked in the hot path in can_can_gw_rcv */

#define MODFUNC(func, op) static void func(struct can_frame *cf, \
                                           struct cf_mod *mod) { op ; }

MODFUNC(mod_and_id, cf->can_id &= mod->modframe.and.can_id)
MODFUNC(mod_and_dlc, cf->can_dlc &= mod->modframe.and.can_dlc)
MODFUNC(mod_and_data, *(u64 *)cf->data &= *(u64 *)mod->modframe.and.data)
MODFUNC(mod_or_id, cf->can_id |= mod->modframe.or.can_id)
MODFUNC(mod_or_dlc, cf->can_dlc |= mod->modframe.or.can_dlc)
MODFUNC(mod_or_data, *(u64 *)cf->data |= *(u64 *)mod->modframe.or.data)
MODFUNC(mod_xor_id, cf->can_id ^= mod->modframe.xor.can_id)
MODFUNC(mod_xor_dlc, cf->can_dlc ^= mod->modframe.xor.can_dlc)
MODFUNC(mod_xor_data, *(u64 *)cf->data ^= *(u64 *)mod->modframe.xor.data)
MODFUNC(mod_set_id, cf->can_id = mod->modframe.set.can_id)
MODFUNC(mod_set_dlc, cf->can_dlc = mod->modframe.set.can_dlc)
MODFUNC(mod_set_data, *(u64 *)cf->data = *(u64 *)mod->modframe.set.data)

static inline void canframecpy(struct can_frame *dst, struct can_frame *src)
{
        /*
         * Copy the struct members separately to ensure that no uninitialized
         * data are copied in the 3 bytes hole of the struct. This is needed
         * to make easy compares of the data in the struct cf_mod.
         */

        dst->can_id = src->can_id;
        dst->can_dlc = src->can_dlc;
        *(u64 *)dst->data = *(u64 *)src->data;
}

static int cgw_chk_csum_parms(s8 fr, s8 to, s8 re)
{
        /*
         * absolute dlc values 0 .. 7 => 0 .. 7, e.g. data [0]
         * relative to received dlc -1 .. -8 :
         * e.g. for received dlc = 8
         * -1 => index = 7 (data[7])
         * -3 => index = 5 (data[5])
         * -8 => index = 0 (data[0])
         */

        if (fr > -9 && fr < 8 &&
            to > -9 && to < 8 &&
            re > -9 && re < 8)
                return 0;
        else
                return -EINVAL;
}

static inline int calc_idx(int idx, int rx_dlc)
{
        if (idx < 0)
                return rx_dlc + idx;
        else
                return idx;
}

static void cgw_csum_xor_rel(struct can_frame *cf, struct cgw_csum_xor *xor)
{
        int from = calc_idx(xor->from_idx, cf->can_dlc);
        int to = calc_idx(xor->to_idx, cf->can_dlc);
        int res = calc_idx(xor->result_idx, cf->can_dlc);
        u8 val = xor->init_xor_val;
        int i;

        if (from < 0 || to < 0 || res < 0)
                return;

        if (from <= to) {
                for (i = from; i <= to; i++)
                        val ^= cf->data[i];
        } else {
                for (i = from; i >= to; i--)
                        val ^= cf->data[i];
        }

        cf->data[res] = val;
}

static void cgw_csum_xor_pos(struct can_frame *cf, struct cgw_csum_xor *xor)
{
        u8 val = xor->init_xor_val;
        int i;

        for (i = xor->from_idx; i <= xor->to_idx; i++)
                val ^= cf->data[i];

        cf->data[xor->result_idx] = val;
}

static void cgw_csum_xor_neg(struct can_frame *cf, struct cgw_csum_xor *xor)
{
        u8 val = xor->init_xor_val;
        int i;

        for (i = xor->from_idx; i >= xor->to_idx; i--)
                val ^= cf->data[i];

        cf->data[xor->result_idx] = val;
}

static void cgw_csum_crc8_rel(struct can_frame *cf, struct cgw_csum_crc8 *crc8)
{
        int from = calc_idx(crc8->from_idx, cf->can_dlc);
        int to = calc_idx(crc8->to_idx, cf->can_dlc);
        int res = calc_idx(crc8->result_idx, cf->can_dlc);
        u8 crc = crc8->init_crc_val;
        int i;

        if (from < 0 || to < 0 || res < 0)
                return;

        if (from <= to) {
                for (i = crc8->from_idx; i <= crc8->to_idx; i++)
                        crc = crc8->crctab[crc^cf->data[i]];
        } else {
                for (i = crc8->from_idx; i >= crc8->to_idx; i--)
                        crc = crc8->crctab[crc^cf->data[i]];
        }

        switch (crc8->profile) {

        case CGW_CRC8PRF_1U8:
                crc = crc8->crctab[crc^crc8->profile_data[0]];
                break;

        case  CGW_CRC8PRF_16U8:
                crc = crc8->crctab[crc^crc8->profile_data[cf->data[1] & 0xF]];
                break;

        case CGW_CRC8PRF_SFFID_XOR:
                crc = crc8->crctab[crc^(cf->can_id & 0xFF)^
                                   (cf->can_id >> 8 & 0xFF)];
                break;

        }

        cf->data[crc8->result_idx] = crc^crc8->final_xor_val;
}

static void cgw_csum_crc8_pos(struct can_frame *cf, struct cgw_csum_crc8 *crc8)
{
        u8 crc = crc8->init_crc_val;
        int i;

        for (i = crc8->from_idx; i <= crc8->to_idx; i++)
                crc = crc8->crctab[crc^cf->data[i]];

        switch (crc8->profile) {

        case CGW_CRC8PRF_1U8:
                crc = crc8->crctab[crc^crc8->profile_data[0]];
                break;

        case  CGW_CRC8PRF_16U8:
                crc = crc8->crctab[crc^crc8->profile_data[cf->data[1] & 0xF]];
                break;

        case CGW_CRC8PRF_SFFID_XOR:
                crc = crc8->crctab[crc^(cf->can_id & 0xFF)^
                                   (cf->can_id >> 8 & 0xFF)];
                break;
        }

        cf->data[crc8->result_idx] = crc^crc8->final_xor_val;
}

static void cgw_csum_crc8_neg(struct can_frame *cf, struct cgw_csum_crc8 *crc8)
{
        u8 crc = crc8->init_crc_val;
        int i;

        for (i = crc8->from_idx; i >= crc8->to_idx; i--)
                crc = crc8->crctab[crc^cf->data[i]];

        switch (crc8->profile) {

        case CGW_CRC8PRF_1U8:
                crc = crc8->crctab[crc^crc8->profile_data[0]];
                break;

        case  CGW_CRC8PRF_16U8:
                crc = crc8->crctab[crc^crc8->profile_data[cf->data[1] & 0xF]];
                break;

        case CGW_CRC8PRF_SFFID_XOR:
                crc = crc8->crctab[crc^(cf->can_id & 0xFF)^
                                   (cf->can_id >> 8 & 0xFF)];
                break;
        }

        cf->data[crc8->result_idx] = crc^crc8->final_xor_val;
}

/* the receive & process & send function */
static void can_can_gw_rcv(struct sk_buff *skb, void *data)
{
        struct cgw_job *gwj = (struct cgw_job *)data;
        struct can_frame *cf;
        struct sk_buff *nskb;
        int modidx = 0;

        /*
         * Do not handle CAN frames routed more than 'max_hops' times.
         * In general we should never catch this delimiter which is intended
         * to cover a misconfiguration protection (e.g. circular CAN routes).
         *
         * The Controller Area Network controllers only accept CAN frames with
         * correct CRCs - which are not visible in the controller registers.
         * According to skbuff.h documentation the csum_start element for IP
         * checksums is undefined/unsued when ip_summed == CHECKSUM_UNNECESSARY.
         * Only CAN skbs can be processed here which already have this property.
         */

#define cgw_hops(skb) ((skb)->csum_start)

        BUG_ON(skb->ip_summed != CHECKSUM_UNNECESSARY);

        if (cgw_hops(skb) >= max_hops) {
                /* indicate deleted frames due to misconfiguration */
                gwj->deleted_frames++;
                return;
        }

        if (!(gwj->dst.dev->flags & IFF_UP)) {
                gwj->dropped_frames++;
                return;
        }

        /* is sending the skb back to the incoming interface not allowed? */
        if (!(gwj->flags & CGW_FLAGS_CAN_IIF_TX_OK) &&
            can_skb_prv(skb)->ifindex == gwj->dst.dev->ifindex)
                return;

        /*
         * clone the given skb, which has not been done in can_rcv()
         *
         * When there is at least one modification function activated,
         * we need to copy the skb as we want to modify skb->data.
         */
        if (gwj->mod.modfunc[0])
                nskb = skb_copy(skb, GFP_ATOMIC);
        else
                nskb = skb_clone(skb, GFP_ATOMIC);

        if (!nskb) {
                gwj->dropped_frames++;
                return;
        }

        /* put the incremented hop counter in the cloned skb */
        cgw_hops(nskb) = cgw_hops(skb) + 1;
        nskb->dev = gwj->dst.dev;

        /* pointer to modifiable CAN frame */
        cf = (struct can_frame *)nskb->data;

        /* perform preprocessed modification functions if there are any */
        while (modidx < MAX_MODFUNCTIONS && gwj->mod.modfunc[modidx])
                (*gwj->mod.modfunc[modidx++])(cf, &gwj->mod);

        /* check for checksum updates when the CAN frame has been modified */
        if (modidx) {
                if (gwj->mod.csumfunc.crc8)
                        (*gwj->mod.csumfunc.crc8)(cf, &gwj->mod.csum.crc8);

                if (gwj->mod.csumfunc.xor)
                        (*gwj->mod.csumfunc.xor)(cf, &gwj->mod.csum.xor);
        }

        /* clear the skb timestamp if not configured the other way */
        if (!(gwj->flags & CGW_FLAGS_CAN_SRC_TSTAMP))
                nskb->tstamp.tv64 = 0;

        /* send to netdevice */
        if (can_send(nskb, gwj->flags & CGW_FLAGS_CAN_ECHO))
                gwj->dropped_frames++;
        else
                gwj->handled_frames++;
}

static inline int cgw_register_filter(struct cgw_job *gwj)
{
        return can_rx_register(gwj->src.dev, gwj->ccgw.filter.can_id,
                               gwj->ccgw.filter.can_mask, can_can_gw_rcv,
                               gwj, "gw");
}

static inline void cgw_unregister_filter(struct cgw_job *gwj)
{
        can_rx_unregister(gwj->src.dev, gwj->ccgw.filter.can_id,
                          gwj->ccgw.filter.can_mask, can_can_gw_rcv, gwj);
}

static int cgw_notifier(struct notifier_block *nb,
                        unsigned long msg, void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);

        if (!net_eq(dev_net(dev), &init_net))
                return NOTIFY_DONE;
        if (dev->type != ARPHRD_CAN)
                return NOTIFY_DONE;

        if (msg == NETDEV_UNREGISTER) {

                struct cgw_job *gwj = NULL;
                struct hlist_node *nx;

                ASSERT_RTNL();

                hlist_for_each_entry_safe(gwj, nx, &cgw_list, list) {

                        if (gwj->src.dev == dev || gwj->dst.dev == dev) {
                                hlist_del(&gwj->list);
                                cgw_unregister_filter(gwj);
                                kmem_cache_free(cgw_cache, gwj);
                        }
                }
        }

        return NOTIFY_DONE;
}

static int cgw_put_job(struct sk_buff *skb, struct cgw_job *gwj, int type,
                       u32 pid, u32 seq, int flags)
{
        struct cgw_frame_mod mb;
        struct rtcanmsg *rtcan;
        struct nlmsghdr *nlh;

        nlh = nlmsg_put(skb, pid, seq, type, sizeof(*rtcan), flags);
        if (!nlh)
                return -EMSGSIZE;

        rtcan = nlmsg_data(nlh);
        rtcan->can_family = AF_CAN;
        rtcan->gwtype = gwj->gwtype;
        rtcan->flags = gwj->flags;

        /* add statistics if available */

        if (gwj->handled_frames) {
                if (nla_put_u32(skb, CGW_HANDLED, gwj->handled_frames) < 0)
                        goto cancel;
        }

        if (gwj->dropped_frames) {
                if (nla_put_u32(skb, CGW_DROPPED, gwj->dropped_frames) < 0)
                        goto cancel;
        }

        if (gwj->deleted_frames) {
                if (nla_put_u32(skb, CGW_DELETED, gwj->deleted_frames) < 0)
                        goto cancel;
        }

        /* check non default settings of attributes */

        if (gwj->mod.modtype.and) {
                memcpy(&mb.cf, &gwj->mod.modframe.and, sizeof(mb.cf));
                mb.modtype = gwj->mod.modtype.and;
                if (nla_put(skb, CGW_MOD_AND, sizeof(mb), &mb) < 0)
                        goto cancel;
        }

        if (gwj->mod.modtype.or) {
                memcpy(&mb.cf, &gwj->mod.modframe.or, sizeof(mb.cf));
                mb.modtype = gwj->mod.modtype.or;
                if (nla_put(skb, CGW_MOD_OR, sizeof(mb), &mb) < 0)
                        goto cancel;
        }

        if (gwj->mod.modtype.xor) {
                memcpy(&mb.cf, &gwj->mod.modframe.xor, sizeof(mb.cf));
                mb.modtype = gwj->mod.modtype.xor;
                if (nla_put(skb, CGW_MOD_XOR, sizeof(mb), &mb) < 0)
                        goto cancel;
        }

        if (gwj->mod.modtype.set) {
                memcpy(&mb.cf, &gwj->mod.modframe.set, sizeof(mb.cf));
                mb.modtype = gwj->mod.modtype.set;
                if (nla_put(skb, CGW_MOD_SET, sizeof(mb), &mb) < 0)
                        goto cancel;
        }

        if (gwj->mod.csumfunc.crc8) {
                if (nla_put(skb, CGW_CS_CRC8, CGW_CS_CRC8_LEN,
                            &gwj->mod.csum.crc8) < 0)
                        goto cancel;
        }

        if (gwj->mod.csumfunc.xor) {
                if (nla_put(skb, CGW_CS_XOR, CGW_CS_XOR_LEN,
                            &gwj->mod.csum.xor) < 0)
                        goto cancel;
        }

        if (gwj->gwtype == CGW_TYPE_CAN_CAN) {

                if (gwj->ccgw.filter.can_id || gwj->ccgw.filter.can_mask) {
                        if (nla_put(skb, CGW_FILTER, sizeof(struct can_filter),
                                    &gwj->ccgw.filter) < 0)
                                goto cancel;
                }

                if (nla_put_u32(skb, CGW_SRC_IF, gwj->ccgw.src_idx) < 0)
                        goto cancel;

                if (nla_put_u32(skb, CGW_DST_IF, gwj->ccgw.dst_idx) < 0)
                        goto cancel;
        }

        return nlmsg_end(skb, nlh);

cancel:
        nlmsg_cancel(skb, nlh);
        return -EMSGSIZE;
}

/* Dump information about all CAN gateway jobs, in response to RTM_GETROUTE */
static int cgw_dump_jobs(struct sk_buff *skb, struct netlink_callback *cb)
{
        struct cgw_job *gwj = NULL;
        int idx = 0;
        int s_idx = cb->args[0];

        rcu_read_lock();
        hlist_for_each_entry_rcu(gwj, &cgw_list, list) {
                if (idx < s_idx)
                        goto cont;

                if (cgw_put_job(skb, gwj, RTM_NEWROUTE, NETLINK_CB(cb->skb).portid,
                    cb->nlh->nlmsg_seq, NLM_F_MULTI) < 0)
                        break;
cont:
                idx++;
        }
        rcu_read_unlock();

        cb->args[0] = idx;

        return skb->len;
}

static const struct nla_policy cgw_policy[CGW_MAX+1] = {
        [CGW_MOD_AND]   = { .len = sizeof(struct cgw_frame_mod) },
        [CGW_MOD_OR]    = { .len = sizeof(struct cgw_frame_mod) },
        [CGW_MOD_XOR]   = { .len = sizeof(struct cgw_frame_mod) },
        [CGW_MOD_SET]   = { .len = sizeof(struct cgw_frame_mod) },
        [CGW_CS_XOR]    = { .len = sizeof(struct cgw_csum_xor) },
        [CGW_CS_CRC8]   = { .len = sizeof(struct cgw_csum_crc8) },
        [CGW_SRC_IF]    = { .type = NLA_U32 },
        [CGW_DST_IF]    = { .type = NLA_U32 },
        [CGW_FILTER]    = { .len = sizeof(struct can_filter) },
};

/* check for common and gwtype specific attributes */
static int cgw_parse_attr(struct nlmsghdr *nlh, struct cf_mod *mod,
                          u8 gwtype, void *gwtypeattr)
{
        struct nlattr *tb[CGW_MAX+1];
        struct cgw_frame_mod mb;
        int modidx = 0;
        int err = 0;

        /* initialize modification & checksum data space */
        memset(mod, 0, sizeof(*mod));

        err = nlmsg_parse(nlh, sizeof(struct rtcanmsg), tb, CGW_MAX,
                          cgw_policy);
        if (err < 0)
                return err;

        /* check for AND/OR/XOR/SET modifications */

        if (tb[CGW_MOD_AND]) {
                nla_memcpy(&mb, tb[CGW_MOD_AND], CGW_MODATTR_LEN);

                canframecpy(&mod->modframe.and, &mb.cf);
                mod->modtype.and = mb.modtype;

                if (mb.modtype & CGW_MOD_ID)
                        mod->modfunc[modidx++] = mod_and_id;

                if (mb.modtype & CGW_MOD_DLC)
                        mod->modfunc[modidx++] = mod_and_dlc;

                if (mb.modtype & CGW_MOD_DATA)
                        mod->modfunc[modidx++] = mod_and_data;
        }

        if (tb[CGW_MOD_OR]) {
                nla_memcpy(&mb, tb[CGW_MOD_OR], CGW_MODATTR_LEN);

                canframecpy(&mod->modframe.or, &mb.cf);
                mod->modtype.or = mb.modtype;

                if (mb.modtype & CGW_MOD_ID)
                        mod->modfunc[modidx++] = mod_or_id;

                if (mb.modtype & CGW_MOD_DLC)
                        mod->modfunc[modidx++] = mod_or_dlc;

                if (mb.modtype & CGW_MOD_DATA)
                        mod->modfunc[modidx++] = mod_or_data;
        }

        if (tb[CGW_MOD_XOR]) {
                nla_memcpy(&mb, tb[CGW_MOD_XOR], CGW_MODATTR_LEN);

                canframecpy(&mod->modframe.xor, &mb.cf);
                mod->modtype.xor = mb.modtype;

                if (mb.modtype & CGW_MOD_ID)
                        mod->modfunc[modidx++] = mod_xor_id;

                if (mb.modtype & CGW_MOD_DLC)
                        mod->modfunc[modidx++] = mod_xor_dlc;

                if (mb.modtype & CGW_MOD_DATA)
                        mod->modfunc[modidx++] = mod_xor_data;
        }

        if (tb[CGW_MOD_SET]) {
                nla_memcpy(&mb, tb[CGW_MOD_SET], CGW_MODATTR_LEN);

                canframecpy(&mod->modframe.set, &mb.cf);
                mod->modtype.set = mb.modtype;

                if (mb.modtype & CGW_MOD_ID)
                        mod->modfunc[modidx++] = mod_set_id;

                if (mb.modtype & CGW_MOD_DLC)
                        mod->modfunc[modidx++] = mod_set_dlc;

                if (mb.modtype & CGW_MOD_DATA)
                        mod->modfunc[modidx++] = mod_set_data;
        }

        /* check for checksum operations after CAN frame modifications */
        if (modidx) {

                if (tb[CGW_CS_CRC8]) {
                        struct cgw_csum_crc8 *c = nla_data(tb[CGW_CS_CRC8]);

                        err = cgw_chk_csum_parms(c->from_idx, c->to_idx,
                                                 c->result_idx);
                        if (err)
                                return err;

                        nla_memcpy(&mod->csum.crc8, tb[CGW_CS_CRC8],
                                   CGW_CS_CRC8_LEN);

                        /*
                         * select dedicated processing function to reduce
                         * runtime operations in receive hot path.
                         */
                        if (c->from_idx < 0 || c->to_idx < 0 ||
                            c->result_idx < 0)
                                mod->csumfunc.crc8 = cgw_csum_crc8_rel;
                        else if (c->from_idx <= c->to_idx)
                                mod->csumfunc.crc8 = cgw_csum_crc8_pos;
                        else
                                mod->csumfunc.crc8 = cgw_csum_crc8_neg;
                }

                if (tb[CGW_CS_XOR]) {
                        struct cgw_csum_xor *c = nla_data(tb[CGW_CS_XOR]);

                        err = cgw_chk_csum_parms(c->from_idx, c->to_idx,
                                                 c->result_idx);
                        if (err)
                                return err;

                        nla_memcpy(&mod->csum.xor, tb[CGW_CS_XOR],
                                   CGW_CS_XOR_LEN);

                        /*
                         * select dedicated processing function to reduce
                         * runtime operations in receive hot path.
                         */
                        if (c->from_idx < 0 || c->to_idx < 0 ||
                            c->result_idx < 0)
                                mod->csumfunc.xor = cgw_csum_xor_rel;
                        else if (c->from_idx <= c->to_idx)
                                mod->csumfunc.xor = cgw_csum_xor_pos;
                        else
                                mod->csumfunc.xor = cgw_csum_xor_neg;
                }
        }

        if (gwtype == CGW_TYPE_CAN_CAN) {

                /* check CGW_TYPE_CAN_CAN specific attributes */

                struct can_can_gw *ccgw = (struct can_can_gw *)gwtypeattr;
                memset(ccgw, 0, sizeof(*ccgw));

                /* check for can_filter in attributes */
                if (tb[CGW_FILTER])
                        nla_memcpy(&ccgw->filter, tb[CGW_FILTER],
                                   sizeof(struct can_filter));

                err = -ENODEV;

                /* specifying two interfaces is mandatory */
                if (!tb[CGW_SRC_IF] || !tb[CGW_DST_IF])
                        return err;

                ccgw->src_idx = nla_get_u32(tb[CGW_SRC_IF]);
                ccgw->dst_idx = nla_get_u32(tb[CGW_DST_IF]);

                /* both indices set to 0 for flushing all routing entries */
                if (!ccgw->src_idx && !ccgw->dst_idx)
                        return 0;

                /* only one index set to 0 is an error */
                if (!ccgw->src_idx || !ccgw->dst_idx)
                        return err;
        }

        /* add the checks for other gwtypes here */

        return 0;
}

static int cgw_create_job(struct sk_buff *skb,  struct nlmsghdr *nlh)
{
        struct rtcanmsg *r;
        struct cgw_job *gwj;
        int err = 0;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        if (nlmsg_len(nlh) < sizeof(*r))
                return -EINVAL;

        r = nlmsg_data(nlh);
        if (r->can_family != AF_CAN)
                return -EPFNOSUPPORT;

        /* so far we only support CAN -> CAN routings */
        if (r->gwtype != CGW_TYPE_CAN_CAN)
                return -EINVAL;

        gwj = kmem_cache_alloc(cgw_cache, GFP_KERNEL);
        if (!gwj)
                return -ENOMEM;

        gwj->handled_frames = 0;
        gwj->dropped_frames = 0;
        gwj->deleted_frames = 0;
        gwj->flags = r->flags;
        gwj->gwtype = r->gwtype;

        err = cgw_parse_attr(nlh, &gwj->mod, CGW_TYPE_CAN_CAN, &gwj->ccgw);
        if (err < 0)
                goto out;

        err = -ENODEV;

        /* ifindex == 0 is not allowed for job creation */
        if (!gwj->ccgw.src_idx || !gwj->ccgw.dst_idx)
                goto out;

        gwj->src.dev = dev_get_by_index(&init_net, gwj->ccgw.src_idx);

        if (!gwj->src.dev)
                goto out;

        /* check for CAN netdev not using header_ops - see gw_rcv() */
        if (gwj->src.dev->type != ARPHRD_CAN || gwj->src.dev->header_ops)
                goto put_src_out;

        gwj->dst.dev = dev_get_by_index(&init_net, gwj->ccgw.dst_idx);

        if (!gwj->dst.dev)
                goto put_src_out;

        /* check for CAN netdev not using header_ops - see gw_rcv() */
        if (gwj->dst.dev->type != ARPHRD_CAN || gwj->dst.dev->header_ops)
                goto put_src_dst_out;

        ASSERT_RTNL();

        err = cgw_register_filter(gwj);
        if (!err)
                hlist_add_head_rcu(&gwj->list, &cgw_list);

put_src_dst_out:
        dev_put(gwj->dst.dev);
put_src_out:
        dev_put(gwj->src.dev);
out:
        if (err)
                kmem_cache_free(cgw_cache, gwj);

        return err;
}

static void cgw_remove_all_jobs(void)
{
        struct cgw_job *gwj = NULL;
        struct hlist_node *nx;

        ASSERT_RTNL();

        hlist_for_each_entry_safe(gwj, nx, &cgw_list, list) {
                hlist_del(&gwj->list);
                cgw_unregister_filter(gwj);
                kmem_cache_free(cgw_cache, gwj);
        }
}

static int cgw_remove_job(struct sk_buff *skb,  struct nlmsghdr *nlh)
{
        struct cgw_job *gwj = NULL;
        struct hlist_node *nx;
        struct rtcanmsg *r;
        struct cf_mod mod;
        struct can_can_gw ccgw;
        int err = 0;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        if (nlmsg_len(nlh) < sizeof(*r))
                return -EINVAL;

        r = nlmsg_data(nlh);
        if (r->can_family != AF_CAN)
                return -EPFNOSUPPORT;

        /* so far we only support CAN -> CAN routings */
        if (r->gwtype != CGW_TYPE_CAN_CAN)
                return -EINVAL;

        err = cgw_parse_attr(nlh, &mod, CGW_TYPE_CAN_CAN, &ccgw);
        if (err < 0)
                return err;

        /* two interface indices both set to 0 => remove all entries */
        if (!ccgw.src_idx && !ccgw.dst_idx) {
                cgw_remove_all_jobs();
                return 0;
        }

        err = -EINVAL;

        ASSERT_RTNL();

        /* remove only the first matching entry */
        hlist_for_each_entry_safe(gwj, nx, &cgw_list, list) {

                if (gwj->flags != r->flags)
                        continue;

                if (memcmp(&gwj->mod, &mod, sizeof(mod)))
                        continue;

                /* if (r->gwtype == CGW_TYPE_CAN_CAN) - is made sure here */
                if (memcmp(&gwj->ccgw, &ccgw, sizeof(ccgw)))
                        continue;

                hlist_del(&gwj->list);
                cgw_unregister_filter(gwj);
                kmem_cache_free(cgw_cache, gwj);
                err = 0;
                break;
        }

        return err;
}

static __init int cgw_module_init(void)
{
        /* sanitize given module parameter */
        max_hops = clamp_t(unsigned int, max_hops, CGW_MIN_HOPS, CGW_MAX_HOPS);

        pr_info("can: netlink gateway (rev " CAN_GW_VERSION ") max_hops=%d\n",
                max_hops);

        cgw_cache = kmem_cache_create("can_gw", sizeof(struct cgw_job),
                                      0, 0, NULL);

        if (!cgw_cache)
                return -ENOMEM;

        /* set notifier */
        notifier.notifier_call = cgw_notifier;
        register_netdevice_notifier(&notifier);

        if (__rtnl_register(PF_CAN, RTM_GETROUTE, NULL, cgw_dump_jobs, NULL)) {
                unregister_netdevice_notifier(&notifier);
                kmem_cache_destroy(cgw_cache);
                return -ENOBUFS;
        }

        /* Only the first call to __rtnl_register can fail */
        __rtnl_register(PF_CAN, RTM_NEWROUTE, cgw_create_job, NULL, NULL);
        __rtnl_register(PF_CAN, RTM_DELROUTE, cgw_remove_job, NULL, NULL);

        return 0;
}

static __exit void cgw_module_exit(void)
{
        rtnl_unregister_all(PF_CAN);

        unregister_netdevice_notifier(&notifier);

        rtnl_lock();
        cgw_remove_all_jobs();
        rtnl_unlock();

        rcu_barrier(); /* Wait for completion of call_rcu()'s */

        kmem_cache_destroy(cgw_cache);
}

module_init(cgw_module_init);
module_exit(cgw_module_exit);