af_can.c

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/*
 * af_can.c - Protocol family CAN core module
 *            (used by different CAN protocol modules)
 *
 * Copyright (c) 2002-2007 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/stddef.h>
#include <linux/init.h>
#include <linux/kmod.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/uaccess.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/socket.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>
#include <linux/skbuff.h>
#include <linux/can.h>
#include <linux/can/core.h>
#include <linux/ratelimit.h>
#include <net/net_namespace.h>
#include <net/sock.h>

#include "af_can.h"

static __initconst const char banner[] = KERN_INFO
    "can: controller area network core (" CAN_VERSION_STRING ")\n";

MODULE_DESCRIPTION("Controller Area Network PF_CAN core");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Urs Thuermann <[email protected]>, "
          "Oliver Hartkopp <[email protected]>");

MODULE_ALIAS_NETPROTO(PF_CAN);

static int stats_timer __read_mostly = 1;
module_param(stats_timer, int, S_IRUGO);
MODULE_PARM_DESC(stats_timer, "enable timer for statistics (default:on)");

/* receive filters subscribed for 'all' CAN devices */
struct dev_rcv_lists can_rx_alldev_list;
static DEFINE_SPINLOCK(can_rcvlists_lock);

static struct kmem_cache *rcv_cache __read_mostly;

/* table of registered CAN protocols */
static const struct can_proto *proto_tab[CAN_NPROTO] __read_mostly;
static DEFINE_MUTEX(proto_tab_lock);

struct timer_list can_stattimer;   /* timer for statistics update */
struct s_stats    can_stats;       /* packet statistics */
struct s_pstats   can_pstats;      /* receive list statistics */

/*
 * af_can socket functions
 */

int can_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
{
    struct sock *sk = sock->sk;

    switch (cmd) {

    case SIOCGSTAMP:
        return sock_get_timestamp(sk, (struct timeval __user *)arg);

    default:
        return -ENOIOCTLCMD;
    }
}
EXPORT_SYMBOL(can_ioctl);

static void can_sock_destruct(struct sock *sk)
{
    skb_queue_purge(&sk->sk_receive_queue);
}

static const struct can_proto *can_get_proto(int protocol)
{
    const struct can_proto *cp;

    rcu_read_lock();
    cp = rcu_dereference(proto_tab[protocol]);
    if (cp && !try_module_get(cp->prot->owner))
        cp = NULL;
    rcu_read_unlock();

    return cp;
}

static inline void can_put_proto(const struct can_proto *cp)
{
    module_put(cp->prot->owner);
}

static int can_create(struct net *net, struct socket *sock, int protocol,
              int kern)
{
    struct sock *sk;
    const struct can_proto *cp;
    int err = 0;

    sock->state = SS_UNCONNECTED;

    if (protocol < 0 || protocol >= CAN_NPROTO)
        return -EINVAL;

    if (!net_eq(net, &init_net))
        return -EAFNOSUPPORT;

    cp = can_get_proto(protocol);

#ifdef CONFIG_MODULES
    if (!cp) {
        /* try to load protocol module if kernel is modular */

        err = request_module("can-proto-%d", protocol);

        /*
         * In case of error we only print a message but don't
         * return the error code immediately.  Below we will
         * return -EPROTONOSUPPORT
         */
        if (err)
            printk_ratelimited(KERN_ERR "can: request_module "
                   "(can-proto-%d) failed.\n", protocol);

        cp = can_get_proto(protocol);
    }
#endif

    /* check for available protocol and correct usage */

    if (!cp)
        return -EPROTONOSUPPORT;

    if (cp->type != sock->type) {
        err = -EPROTOTYPE;
        goto errout;
    }

    sock->ops = cp->ops;

    sk = sk_alloc(net, PF_CAN, GFP_KERNEL, cp->prot);
    if (!sk) {
        err = -ENOMEM;
        goto errout;
    }

    sock_init_data(sock, sk);
    sk->sk_destruct = can_sock_destruct;

    if (sk->sk_prot->init)
        err = sk->sk_prot->init(sk);

    if (err) {
        /* release sk on errors */
        sock_orphan(sk);
        sock_put(sk);
    }

 errout:
    can_put_proto(cp);
    return err;
}

/*
 * af_can tx path
 */

int can_send(struct sk_buff *skb, int loop)
{
    struct sk_buff *newskb = NULL;
    struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
    int err = -EINVAL;

    if (skb->len == CAN_MTU) {
        skb->protocol = htons(ETH_P_CAN);
        if (unlikely(cfd->len > CAN_MAX_DLEN))
            goto inval_skb;
    } else if (skb->len == CANFD_MTU) {
        skb->protocol = htons(ETH_P_CANFD);
        if (unlikely(cfd->len > CANFD_MAX_DLEN))
            goto inval_skb;
    } else
        goto inval_skb;

    /*
     * Make sure the CAN frame can pass the selected CAN netdevice.
     * As structs can_frame and canfd_frame are similar, we can provide
     * CAN FD frames to legacy CAN drivers as long as the length is <= 8
     */
    if (unlikely(skb->len > skb->dev->mtu && cfd->len > CAN_MAX_DLEN)) {
        err = -EMSGSIZE;
        goto inval_skb;
    }

    if (unlikely(skb->dev->type != ARPHRD_CAN)) {
        err = -EPERM;
        goto inval_skb;
    }

    if (unlikely(!(skb->dev->flags & IFF_UP))) {
        err = -ENETDOWN;
        goto inval_skb;
    }

    skb_reset_network_header(skb);
    skb_reset_transport_header(skb);

    if (loop) {
        /* local loopback of sent CAN frames */

        /* indication for the CAN driver: do loopback */
        skb->pkt_type = PACKET_LOOPBACK;

        /*
         * The reference to the originating sock may be required
         * by the receiving socket to check whether the frame is
         * its own. Example: can_raw sockopt CAN_RAW_RECV_OWN_MSGS
         * Therefore we have to ensure that skb->sk remains the
         * reference to the originating sock by restoring skb->sk
         * after each skb_clone() or skb_orphan() usage.
         */

        if (!(skb->dev->flags & IFF_ECHO)) {
            /*
             * If the interface is not capable to do loopback
             * itself, we do it here.
             */
            newskb = skb_clone(skb, GFP_ATOMIC);
            if (!newskb) {
                kfree_skb(skb);
                return -ENOMEM;
            }

            newskb->sk = skb->sk;
            newskb->ip_summed = CHECKSUM_UNNECESSARY;
            newskb->pkt_type = PACKET_BROADCAST;
        }
    } else {
        /* indication for the CAN driver: no loopback required */
        skb->pkt_type = PACKET_HOST;
    }

    /* send to netdevice */
    err = dev_queue_xmit(skb);
    if (err > 0)
        err = net_xmit_errno(err);

    if (err) {
        kfree_skb(newskb);
        return err;
    }

    if (newskb)
        netif_rx_ni(newskb);

    /* update statistics */
    can_stats.tx_frames++;
    can_stats.tx_frames_delta++;

    return 0;

inval_skb:
    kfree_skb(skb);
    return err;
}
EXPORT_SYMBOL(can_send);

/*
 * af_can rx path
 */

static struct dev_rcv_lists *find_dev_rcv_lists(struct net_device *dev)
{
    if (!dev)
        return &can_rx_alldev_list;
    else
        return (struct dev_rcv_lists *)dev->ml_priv;
}

static struct hlist_head *find_rcv_list(canid_t *can_id, canid_t *mask,
                    struct dev_rcv_lists *d)
{
    canid_t inv = *can_id & CAN_INV_FILTER; /* save flag before masking */

    /* filter for error message frames in extra filterlist */
    if (*mask & CAN_ERR_FLAG) {
        /* clear CAN_ERR_FLAG in filter entry */
        *mask &= CAN_ERR_MASK;
        return &d->rx[RX_ERR];
    }

    /* with cleared CAN_ERR_FLAG we have a simple mask/value filterpair */

#define CAN_EFF_RTR_FLAGS (CAN_EFF_FLAG | CAN_RTR_FLAG)

    /* ensure valid values in can_mask for 'SFF only' frame filtering */
    if ((*mask & CAN_EFF_FLAG) && !(*can_id & CAN_EFF_FLAG))
        *mask &= (CAN_SFF_MASK | CAN_EFF_RTR_FLAGS);

    /* reduce condition testing at receive time */
    *can_id &= *mask;

    /* inverse can_id/can_mask filter */
    if (inv)
        return &d->rx[RX_INV];

    /* mask == 0 => no condition testing at receive time */
    if (!(*mask))
        return &d->rx[RX_ALL];

    /* extra filterlists for the subscription of a single non-RTR can_id */
    if (((*mask & CAN_EFF_RTR_FLAGS) == CAN_EFF_RTR_FLAGS) &&
        !(*can_id & CAN_RTR_FLAG)) {

        if (*can_id & CAN_EFF_FLAG) {
            if (*mask == (CAN_EFF_MASK | CAN_EFF_RTR_FLAGS)) {
                /* RFC: a future use-case for hash-tables? */
                return &d->rx[RX_EFF];
            }
        } else {
            if (*mask == (CAN_SFF_MASK | CAN_EFF_RTR_FLAGS))
                return &d->rx_sff[*can_id];
        }
    }

    /* default: filter via can_id/can_mask */
    return &d->rx[RX_FIL];
}

int can_rx_register(struct net_device *dev, canid_t can_id, canid_t mask,
            void (*func)(struct sk_buff *, void *), void *data,
            char *ident)
{
    struct receiver *r;
    struct hlist_head *rl;
    struct dev_rcv_lists *d;
    int err = 0;

    /* insert new receiver  (dev,canid,mask) -> (func,data) */

    if (dev && dev->type != ARPHRD_CAN)
        return -ENODEV;

    r = kmem_cache_alloc(rcv_cache, GFP_KERNEL);
    if (!r)
        return -ENOMEM;

    spin_lock(&can_rcvlists_lock);

    d = find_dev_rcv_lists(dev);
    if (d) {
        rl = find_rcv_list(&can_id, &mask, d);

        r->can_id  = can_id;
        r->mask    = mask;
        r->matches = 0;
        r->func    = func;
        r->data    = data;
        r->ident   = ident;

        hlist_add_head_rcu(&r->list, rl);
        d->entries++;

        can_pstats.rcv_entries++;
        if (can_pstats.rcv_entries_max < can_pstats.rcv_entries)
            can_pstats.rcv_entries_max = can_pstats.rcv_entries;
    } else {
        kmem_cache_free(rcv_cache, r);
        err = -ENODEV;
    }

    spin_unlock(&can_rcvlists_lock);

    return err;
}
EXPORT_SYMBOL(can_rx_register);

/*
 * can_rx_delete_receiver - rcu callback for single receiver entry removal
 */
static void can_rx_delete_receiver(struct rcu_head *rp)
{
    struct receiver *r = container_of(rp, struct receiver, rcu);

    kmem_cache_free(rcv_cache, r);
}

void can_rx_unregister(struct net_device *dev, canid_t can_id, canid_t mask,
               void (*func)(struct sk_buff *, void *), void *data)
{
    struct receiver *r = NULL;
    struct hlist_head *rl;
    struct hlist_node *next;
    struct dev_rcv_lists *d;

    if (dev && dev->type != ARPHRD_CAN)
        return;

    spin_lock(&can_rcvlists_lock);

    d = find_dev_rcv_lists(dev);
    if (!d) {
        printk(KERN_ERR "BUG: receive list not found for "
               "dev %s, id %03X, mask %03X\n",
               DNAME(dev), can_id, mask);
        goto out;
    }

    rl = find_rcv_list(&can_id, &mask, d);

    /*
     * Search the receiver list for the item to delete.  This should
     * exist, since no receiver may be unregistered that hasn't
     * been registered before.
     */

    hlist_for_each_entry_rcu(r, next, rl, list) {
        if (r->can_id == can_id && r->mask == mask &&
            r->func == func && r->data == data)
            break;
    }

    /*
     * Check for bugs in CAN protocol implementations:
     * If no matching list item was found, the list cursor variable next
     * will be NULL, while r will point to the last item of the list.
     */

    if (!next) {
        printk(KERN_ERR "BUG: receive list entry not found for "
               "dev %s, id %03X, mask %03X\n",
               DNAME(dev), can_id, mask);
        r = NULL;
        goto out;
    }

    hlist_del_rcu(&r->list);
    d->entries--;

    if (can_pstats.rcv_entries > 0)
        can_pstats.rcv_entries--;

    /* remove device structure requested by NETDEV_UNREGISTER */
    if (d->remove_on_zero_entries && !d->entries) {
        kfree(d);
        dev->ml_priv = NULL;
    }

 out:
    spin_unlock(&can_rcvlists_lock);

    /* schedule the receiver item for deletion */
    if (r)
        call_rcu(&r->rcu, can_rx_delete_receiver);
}
EXPORT_SYMBOL(can_rx_unregister);

static inline void deliver(struct sk_buff *skb, struct receiver *r)
{
    r->func(skb, r->data);
    r->matches++;
}

static int can_rcv_filter(struct dev_rcv_lists *d, struct sk_buff *skb)
{
    struct receiver *r;
    struct hlist_node *n;
    int matches = 0;
    struct can_frame *cf = (struct can_frame *)skb->data;
    canid_t can_id = cf->can_id;

    if (d->entries == 0)
        return 0;

    if (can_id & CAN_ERR_FLAG) {
        /* check for error message frame entries only */
        hlist_for_each_entry_rcu(r, n, &d->rx[RX_ERR], list) {
            if (can_id & r->mask) {
                deliver(skb, r);
                matches++;
            }
        }
        return matches;
    }

    /* check for unfiltered entries */
    hlist_for_each_entry_rcu(r, n, &d->rx[RX_ALL], list) {
        deliver(skb, r);
        matches++;
    }

    /* check for can_id/mask entries */
    hlist_for_each_entry_rcu(r, n, &d->rx[RX_FIL], list) {
        if ((can_id & r->mask) == r->can_id) {
            deliver(skb, r);
            matches++;
        }
    }

    /* check for inverted can_id/mask entries */
    hlist_for_each_entry_rcu(r, n, &d->rx[RX_INV], list) {
        if ((can_id & r->mask) != r->can_id) {
            deliver(skb, r);
            matches++;
        }
    }

    /* check filterlists for single non-RTR can_ids */
    if (can_id & CAN_RTR_FLAG)
        return matches;

    if (can_id & CAN_EFF_FLAG) {
        hlist_for_each_entry_rcu(r, n, &d->rx[RX_EFF], list) {
            if (r->can_id == can_id) {
                deliver(skb, r);
                matches++;
            }
        }
    } else {
        can_id &= CAN_SFF_MASK;
        hlist_for_each_entry_rcu(r, n, &d->rx_sff[can_id], list) {
            deliver(skb, r);
            matches++;
        }
    }

    return matches;
}

static void can_receive(struct sk_buff *skb, struct net_device *dev)
{
    struct dev_rcv_lists *d;
    int matches;

    /* update statistics */
    can_stats.rx_frames++;
    can_stats.rx_frames_delta++;

    rcu_read_lock();

    /* deliver the packet to sockets listening on all devices */
    matches = can_rcv_filter(&can_rx_alldev_list, skb);

    /* find receive list for this device */
    d = find_dev_rcv_lists(dev);
    if (d)
        matches += can_rcv_filter(d, skb);

    rcu_read_unlock();

    /* consume the skbuff allocated by the netdevice driver */
    consume_skb(skb);

    if (matches > 0) {
        can_stats.matches++;
        can_stats.matches_delta++;
    }
}

static int can_rcv(struct sk_buff *skb, struct net_device *dev,
           struct packet_type *pt, struct net_device *orig_dev)
{
    struct canfd_frame *cfd = (struct canfd_frame *)skb->data;

    if (unlikely(!net_eq(dev_net(dev), &init_net)))
        goto drop;

    if (WARN_ONCE(dev->type != ARPHRD_CAN ||
              skb->len != CAN_MTU ||
              cfd->len > CAN_MAX_DLEN,
              "PF_CAN: dropped non conform CAN skbuf: "
              "dev type %d, len %d, datalen %d\n",
              dev->type, skb->len, cfd->len))
        goto drop;

    can_receive(skb, dev);
    return NET_RX_SUCCESS;

drop:
    kfree_skb(skb);
    return NET_RX_DROP;
}

static int canfd_rcv(struct sk_buff *skb, struct net_device *dev,
           struct packet_type *pt, struct net_device *orig_dev)
{
    struct canfd_frame *cfd = (struct canfd_frame *)skb->data;

    if (unlikely(!net_eq(dev_net(dev), &init_net)))
        goto drop;

    if (WARN_ONCE(dev->type != ARPHRD_CAN ||
              skb->len != CANFD_MTU ||
              cfd->len > CANFD_MAX_DLEN,
              "PF_CAN: dropped non conform CAN FD skbuf: "
              "dev type %d, len %d, datalen %d\n",
              dev->type, skb->len, cfd->len))
        goto drop;

    can_receive(skb, dev);
    return NET_RX_SUCCESS;

drop:
    kfree_skb(skb);
    return NET_RX_DROP;
}

/*
 * af_can protocol functions
 */

int can_proto_register(const struct can_proto *cp)
{
    int proto = cp->protocol;
    int err = 0;

    if (proto < 0 || proto >= CAN_NPROTO) {
        printk(KERN_ERR "can: protocol number %d out of range\n",
               proto);
        return -EINVAL;
    }

    err = proto_register(cp->prot, 0);
    if (err < 0)
        return err;

    mutex_lock(&proto_tab_lock);

    if (proto_tab[proto]) {
        printk(KERN_ERR "can: protocol %d already registered\n",
               proto);
        err = -EBUSY;
    } else
        RCU_INIT_POINTER(proto_tab[proto], cp);

    mutex_unlock(&proto_tab_lock);

    if (err < 0)
        proto_unregister(cp->prot);

    return err;
}
EXPORT_SYMBOL(can_proto_register);

void can_proto_unregister(const struct can_proto *cp)
{
    int proto = cp->protocol;

    mutex_lock(&proto_tab_lock);
    BUG_ON(proto_tab[proto] != cp);
    RCU_INIT_POINTER(proto_tab[proto], NULL);
    mutex_unlock(&proto_tab_lock);

    synchronize_rcu();

    proto_unregister(cp->prot);
}
EXPORT_SYMBOL(can_proto_unregister);

/*
 * af_can notifier to create/remove CAN netdevice specific structs
 */
static int can_notifier(struct notifier_block *nb, unsigned long msg,
            void *data)
{
    struct net_device *dev = (struct net_device *)data;
    struct dev_rcv_lists *d;

    if (!net_eq(dev_net(dev), &init_net))
        return NOTIFY_DONE;

    if (dev->type != ARPHRD_CAN)
        return NOTIFY_DONE;

    switch (msg) {

    case NETDEV_REGISTER:

        /* create new dev_rcv_lists for this device */
        d = kzalloc(sizeof(*d), GFP_KERNEL);
        if (!d) {
            printk(KERN_ERR
                   "can: allocation of receive list failed\n");
            return NOTIFY_DONE;
        }
        BUG_ON(dev->ml_priv);
        dev->ml_priv = d;

        break;

    case NETDEV_UNREGISTER:
        spin_lock(&can_rcvlists_lock);

        d = dev->ml_priv;
        if (d) {
            if (d->entries)
                d->remove_on_zero_entries = 1;
            else {
                kfree(d);
                dev->ml_priv = NULL;
            }
        } else
            printk(KERN_ERR "can: notifier: receive list not "
                   "found for dev %s\n", dev->name);

        spin_unlock(&can_rcvlists_lock);

        break;
    }

    return NOTIFY_DONE;
}

/*
 * af_can module init/exit functions
 */

static struct packet_type can_packet __read_mostly = {
    .type = cpu_to_be16(ETH_P_CAN),
    .func = can_rcv,
};

static struct packet_type canfd_packet __read_mostly = {
    .type = cpu_to_be16(ETH_P_CANFD),
    .func = canfd_rcv,
};

static const struct net_proto_family can_family_ops = {
    .family = PF_CAN,
    .create = can_create,
    .owner  = THIS_MODULE,
};

/* notifier block for netdevice event */
static struct notifier_block can_netdev_notifier __read_mostly = {
    .notifier_call = can_notifier,
};

static __init int can_init(void)
{
    /* check for correct padding to be able to use the structs similarly */
    BUILD_BUG_ON(offsetof(struct can_frame, can_dlc) !=
             offsetof(struct canfd_frame, len) ||
             offsetof(struct can_frame, data) !=
             offsetof(struct canfd_frame, data));

    printk(banner);

    memset(&can_rx_alldev_list, 0, sizeof(can_rx_alldev_list));

    rcv_cache = kmem_cache_create("can_receiver", sizeof(struct receiver),
                      0, 0, NULL);
    if (!rcv_cache)
        return -ENOMEM;

    if (stats_timer) {
        /* the statistics are updated every second (timer triggered) */
        setup_timer(&can_stattimer, can_stat_update, 0);
        mod_timer(&can_stattimer, round_jiffies(jiffies + HZ));
    } else
        can_stattimer.function = NULL;

    can_init_proc();

    /* protocol register */
    sock_register(&can_family_ops);
    register_netdevice_notifier(&can_netdev_notifier);
    dev_add_pack(&can_packet);
    dev_add_pack(&canfd_packet);

    return 0;
}

static __exit void can_exit(void)
{
    struct net_device *dev;

    if (stats_timer)
        del_timer_sync(&can_stattimer);

    can_remove_proc();

    /* protocol unregister */
    dev_remove_pack(&canfd_packet);
    dev_remove_pack(&can_packet);
    unregister_netdevice_notifier(&can_netdev_notifier);
    sock_unregister(PF_CAN);

    /* remove created dev_rcv_lists from still registered CAN devices */
    rcu_read_lock();
    for_each_netdev_rcu(&init_net, dev) {
        if (dev->type == ARPHRD_CAN && dev->ml_priv){

            struct dev_rcv_lists *d = dev->ml_priv;

            BUG_ON(d->entries);
            kfree(d);
            dev->ml_priv = NULL;
        }
    }
    rcu_read_unlock();

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

    kmem_cache_destroy(rcv_cache);
}

module_init(can_init);
module_exit(can_exit);