/*
 * vxcan.c - Virtual CAN Tunnel for cross namespace communication
 *
 * This code is derived from drivers/net/can/vcan.c for the virtual CAN
 * specific parts and from drivers/net/veth.c to implement the netlink API
 * for network interface pairs in a common and established way.
 *
 * Copyright (c) 2017 Oliver Hartkopp <socketcan@hartkopp.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the version 2 of the GNU General Public License
 * 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/can.h>
#include <linux/can/dev.h>
#include <linux/can/skb.h>
#include <linux/can/vxcan.h>
#include <linux/slab.h>
#include <net/rtnetlink.h>

#define DRV_NAME "vxcan"

MODULE_DESCRIPTION("Virtual CAN Tunnel");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Oliver Hartkopp <socketcan@hartkopp.net>");
MODULE_ALIAS_RTNL_LINK(DRV_NAME);

struct vxcan_priv {
        struct net_device __rcu *peer;
};

static netdev_tx_t vxcan_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct vxcan_priv *priv = netdev_priv(dev);
        struct net_device *peer;
        struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
        struct net_device_stats *peerstats, *srcstats = &dev->stats;

        if (can_dropped_invalid_skb(dev, skb))
                return NETDEV_TX_OK;

        rcu_read_lock();
        peer = rcu_dereference(priv->peer);
        if (unlikely(!peer)) {
                kfree_skb(skb);
                dev->stats.tx_dropped++;
                goto out_unlock;
        }

        skb = can_create_echo_skb(skb);
        if (!skb)
                goto out_unlock;

        /* reset CAN GW hop counter */
        skb->csum_start = 0;
        skb->pkt_type   = PACKET_BROADCAST;
        skb->dev        = peer;
        skb->ip_summed  = CHECKSUM_UNNECESSARY;

        if (netif_rx_ni(skb) == NET_RX_SUCCESS) {
                srcstats->tx_packets++;
                srcstats->tx_bytes += cfd->len;
                peerstats = &peer->stats;
                peerstats->rx_packets++;
                peerstats->rx_bytes += cfd->len;
        }

out_unlock:
        rcu_read_unlock();
        return NETDEV_TX_OK;
}


static int vxcan_open(struct net_device *dev)
{
        struct vxcan_priv *priv = netdev_priv(dev);
        struct net_device *peer = rtnl_dereference(priv->peer);

        if (!peer)
                return -ENOTCONN;

        if (peer->flags & IFF_UP) {
                netif_carrier_on(dev);
                netif_carrier_on(peer);
        }
        return 0;
}

static int vxcan_close(struct net_device *dev)
{
        struct vxcan_priv *priv = netdev_priv(dev);
        struct net_device *peer = rtnl_dereference(priv->peer);

        netif_carrier_off(dev);
        if (peer)
                netif_carrier_off(peer);

        return 0;
}

static int vxcan_get_iflink(const struct net_device *dev)
{
        struct vxcan_priv *priv = netdev_priv(dev);
        struct net_device *peer;
        int iflink;

        rcu_read_lock();
        peer = rcu_dereference(priv->peer);
        iflink = peer ? peer->ifindex : 0;
        rcu_read_unlock();

        return iflink;
}

static int vxcan_change_mtu(struct net_device *dev, int new_mtu)
{
        /* Do not allow changing the MTU while running */
        if (dev->flags & IFF_UP)
                return -EBUSY;

        if (new_mtu != CAN_MTU && new_mtu != CANFD_MTU)
                return -EINVAL;

        dev->mtu = new_mtu;
        return 0;
}

static const struct net_device_ops vxcan_netdev_ops = {
        .ndo_open       = vxcan_open,
        .ndo_stop       = vxcan_close,
        .ndo_start_xmit = vxcan_xmit,
        .ndo_get_iflink = vxcan_get_iflink,
        .ndo_change_mtu = vxcan_change_mtu,
};

static void vxcan_setup(struct net_device *dev)
{
        dev->type               = ARPHRD_CAN;
        dev->mtu                = CANFD_MTU;
        dev->hard_header_len    = 0;
        dev->addr_len           = 0;
        dev->tx_queue_len       = 0;
        dev->flags              = (IFF_NOARP|IFF_ECHO);
        dev->netdev_ops         = &vxcan_netdev_ops;
        dev->needs_free_netdev  = true;
}

/* forward declaration for rtnl_create_link() */
static struct rtnl_link_ops vxcan_link_ops;

static int vxcan_newlink(struct net *net, struct net_device *dev,
                         struct nlattr *tb[], struct nlattr *data[],
                         struct netlink_ext_ack *extack)
{
        struct vxcan_priv *priv;
        struct net_device *peer;
        struct net *peer_net;

        struct nlattr *peer_tb[IFLA_MAX + 1], **tbp = tb;
        char ifname[IFNAMSIZ];
        unsigned char name_assign_type;
        struct ifinfomsg *ifmp = NULL;
        int err;

        /* register peer device */
        if (data && data[VXCAN_INFO_PEER]) {
                struct nlattr *nla_peer;

                nla_peer = data[VXCAN_INFO_PEER];
                ifmp = nla_data(nla_peer);
                err = rtnl_nla_parse_ifla(peer_tb,
                                          nla_data(nla_peer) +
                                          sizeof(struct ifinfomsg),
                                          nla_len(nla_peer) -
                                          sizeof(struct ifinfomsg),
                                          NULL);
                if (err < 0)
                        return err;

                tbp = peer_tb;
        }

        if (ifmp && tbp[IFLA_IFNAME]) {
                nla_strlcpy(ifname, tbp[IFLA_IFNAME], IFNAMSIZ);
                name_assign_type = NET_NAME_USER;
        } else {
                snprintf(ifname, IFNAMSIZ, DRV_NAME "%%d");
                name_assign_type = NET_NAME_ENUM;
        }

        peer_net = rtnl_link_get_net(net, tbp);
        if (IS_ERR(peer_net))
                return PTR_ERR(peer_net);

        peer = rtnl_create_link(peer_net, ifname, name_assign_type,
                                &vxcan_link_ops, tbp);
        if (IS_ERR(peer)) {
                put_net(peer_net);
                return PTR_ERR(peer);
        }

        if (ifmp && dev->ifindex)
                peer->ifindex = ifmp->ifi_index;

        err = register_netdevice(peer);
        put_net(peer_net);
        peer_net = NULL;
        if (err < 0) {
                free_netdev(peer);
                return err;
        }

        netif_carrier_off(peer);

        err = rtnl_configure_link(peer, ifmp);
        if (err < 0)
                goto unregister_network_device;

        /* register first device */
        if (tb[IFLA_IFNAME])
                nla_strlcpy(dev->name, tb[IFLA_IFNAME], IFNAMSIZ);
        else
                snprintf(dev->name, IFNAMSIZ, DRV_NAME "%%d");

        err = register_netdevice(dev);
        if (err < 0)
                goto unregister_network_device;

        netif_carrier_off(dev);

        /* cross link the device pair */
        priv = netdev_priv(dev);
        rcu_assign_pointer(priv->peer, peer);

        priv = netdev_priv(peer);
        rcu_assign_pointer(priv->peer, dev);

        return 0;

unregister_network_device:
        unregister_netdevice(peer);
        return err;
}

static void vxcan_dellink(struct net_device *dev, struct list_head *head)
{
        struct vxcan_priv *priv;
        struct net_device *peer;

        priv = netdev_priv(dev);
        peer = rtnl_dereference(priv->peer);

        /* Note : dellink() is called from default_device_exit_batch(),
         * before a rcu_synchronize() point. The devices are guaranteed
         * not being freed before one RCU grace period.
         */
        RCU_INIT_POINTER(priv->peer, NULL);
        unregister_netdevice_queue(dev, head);

        if (peer) {
                priv = netdev_priv(peer);
                RCU_INIT_POINTER(priv->peer, NULL);
                unregister_netdevice_queue(peer, head);
        }
}

static const struct nla_policy vxcan_policy[VXCAN_INFO_MAX + 1] = {
        [VXCAN_INFO_PEER] = { .len = sizeof(struct ifinfomsg) },
};

static struct net *vxcan_get_link_net(const struct net_device *dev)
{
        struct vxcan_priv *priv = netdev_priv(dev);
        struct net_device *peer = rtnl_dereference(priv->peer);

        return peer ? dev_net(peer) : dev_net(dev);
}

static struct rtnl_link_ops vxcan_link_ops = {
        .kind           = DRV_NAME,
        .priv_size      = sizeof(struct vxcan_priv),
        .setup          = vxcan_setup,
        .newlink        = vxcan_newlink,
        .dellink        = vxcan_dellink,
        .policy         = vxcan_policy,
        .maxtype        = VXCAN_INFO_MAX,
        .get_link_net   = vxcan_get_link_net,
};

static __init int vxcan_init(void)
{
        pr_info("vxcan: Virtual CAN Tunnel driver\n");

        return rtnl_link_register(&vxcan_link_ops);
}

static __exit void vxcan_exit(void)
{
        rtnl_link_unregister(&vxcan_link_ops);
}

module_init(vxcan_init);
module_exit(vxcan_exit);