// SPDX-License-Identifier: GPL-2.0-only
/* net/atm/clip.c - RFC1577 Classical IP over ATM */

/* Written 1995-2000 by Werner Almesberger, EPFL LRC/ICA */

#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__

#include <linux/string.h>
#include <linux/errno.h>
#include <linux/kernel.h> /* for UINT_MAX */
#include <linux/module.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/wait.h>
#include <linux/timer.h>
#include <linux/if_arp.h> /* for some manifest constants */
#include <linux/notifier.h>
#include <linux/atm.h>
#include <linux/atmdev.h>
#include <linux/atmclip.h>
#include <linux/atmarp.h>
#include <linux/capability.h>
#include <linux/ip.h> /* for net/route.h */
#include <linux/in.h> /* for struct sockaddr_in */
#include <linux/if.h> /* for IFF_UP */
#include <linux/inetdevice.h>
#include <linux/bitops.h>
#include <linux/poison.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/rcupdate.h>
#include <linux/jhash.h>
#include <linux/slab.h>
#include <net/route.h> /* for struct rtable and routing */
#include <net/icmp.h> /* icmp_send */
#include <net/arp.h>
#include <linux/param.h> /* for HZ */
#include <linux/uaccess.h>
#include <asm/byteorder.h> /* for htons etc. */
#include <linux/atomic.h>

#include "common.h"
#include "resources.h"
#include <net/atmclip.h>

static struct net_device *clip_devs;
static struct atm_vcc *atmarpd;
static struct timer_list idle_timer;
static const struct neigh_ops clip_neigh_ops;

static int to_atmarpd(enum atmarp_ctrl_type type, int itf, __be32 ip)
{
        struct sock *sk;
        struct atmarp_ctrl *ctrl;
        struct sk_buff *skb;

        pr_debug("(%d)\n", type);
        if (!atmarpd)
                return -EUNATCH;
        skb = alloc_skb(sizeof(struct atmarp_ctrl), GFP_ATOMIC);
        if (!skb)
                return -ENOMEM;
        ctrl = skb_put(skb, sizeof(struct atmarp_ctrl));
        ctrl->type = type;
        ctrl->itf_num = itf;
        ctrl->ip = ip;
        atm_force_charge(atmarpd, skb->truesize);

        sk = sk_atm(atmarpd);
        skb_queue_tail(&sk->sk_receive_queue, skb);
        sk->sk_data_ready(sk);
        return 0;
}

static void link_vcc(struct clip_vcc *clip_vcc, struct atmarp_entry *entry)
{
        pr_debug("%p to entry %p (neigh %p)\n", clip_vcc, entry, entry->neigh);
        clip_vcc->entry = entry;
        clip_vcc->xoff = 0;     /* @@@ may overrun buffer by one packet */
        clip_vcc->next = entry->vccs;
        entry->vccs = clip_vcc;
        entry->neigh->used = jiffies;
}

static void unlink_clip_vcc(struct clip_vcc *clip_vcc)
{
        struct atmarp_entry *entry = clip_vcc->entry;
        struct clip_vcc **walk;

        if (!entry) {
                pr_crit("!clip_vcc->entry (clip_vcc %p)\n", clip_vcc);
                return;
        }
        netif_tx_lock_bh(entry->neigh->dev);    /* block clip_start_xmit() */
        entry->neigh->used = jiffies;
        for (walk = &entry->vccs; *walk; walk = &(*walk)->next)
                if (*walk == clip_vcc) {
                        int error;

                        *walk = clip_vcc->next; /* atomic */
                        clip_vcc->entry = NULL;
                        if (clip_vcc->xoff)
                                netif_wake_queue(entry->neigh->dev);
                        if (entry->vccs)
                                goto out;
                        entry->expires = jiffies - 1;
                        /* force resolution or expiration */
                        error = neigh_update(entry->neigh, NULL, NUD_NONE,
                                             NEIGH_UPDATE_F_ADMIN, 0);
                        if (error)
                                pr_crit("neigh_update failed with %d\n", error);
                        goto out;
                }
        pr_crit("ATMARP: failed (entry %p, vcc 0x%p)\n", entry, clip_vcc);
out:
        netif_tx_unlock_bh(entry->neigh->dev);
}

/* The neighbour entry n->lock is held. */
static int neigh_check_cb(struct neighbour *n)
{
        struct atmarp_entry *entry = neighbour_priv(n);
        struct clip_vcc *cv;

        if (n->ops != &clip_neigh_ops)
                return 0;
        for (cv = entry->vccs; cv; cv = cv->next) {
                unsigned long exp = cv->last_use + cv->idle_timeout;

                if (cv->idle_timeout && time_after(jiffies, exp)) {
                        pr_debug("releasing vcc %p->%p of entry %p\n",
                                 cv, cv->vcc, entry);
                        vcc_release_async(cv->vcc, -ETIMEDOUT);
                }
        }

        if (entry->vccs || time_before(jiffies, entry->expires))
                return 0;

        if (refcount_read(&n->refcnt) > 1) {
                struct sk_buff *skb;

                pr_debug("destruction postponed with ref %d\n",
                         refcount_read(&n->refcnt));

                while ((skb = skb_dequeue(&n->arp_queue)) != NULL)
                        dev_kfree_skb(skb);

                return 0;
        }

        pr_debug("expired neigh %p\n", n);
        return 1;
}

static void idle_timer_check(struct timer_list *unused)
{
        write_lock(&arp_tbl.lock);
        __neigh_for_each_release(&arp_tbl, neigh_check_cb);
        mod_timer(&idle_timer, jiffies + CLIP_CHECK_INTERVAL * HZ);
        write_unlock(&arp_tbl.lock);
}

static int clip_arp_rcv(struct sk_buff *skb)
{
        struct atm_vcc *vcc;

        pr_debug("\n");
        vcc = ATM_SKB(skb)->vcc;
        if (!vcc || !atm_charge(vcc, skb->truesize)) {
                dev_kfree_skb_any(skb);
                return 0;
        }
        pr_debug("pushing to %p\n", vcc);
        pr_debug("using %p\n", CLIP_VCC(vcc)->old_push);
        CLIP_VCC(vcc)->old_push(vcc, skb);
        return 0;
}

static const unsigned char llc_oui[] = {
        0xaa,   /* DSAP: non-ISO */
        0xaa,   /* SSAP: non-ISO */
        0x03,   /* Ctrl: Unnumbered Information Command PDU */
        0x00,   /* OUI: EtherType */
        0x00,
        0x00
};

static void clip_push(struct atm_vcc *vcc, struct sk_buff *skb)
{
        struct clip_vcc *clip_vcc = CLIP_VCC(vcc);

        pr_debug("\n");

        if (!clip_devs) {
                atm_return(vcc, skb->truesize);
                kfree_skb(skb);
                return;
        }

        if (!skb) {
                pr_debug("removing VCC %p\n", clip_vcc);
                if (clip_vcc->entry)
                        unlink_clip_vcc(clip_vcc);
                clip_vcc->old_push(vcc, NULL);  /* pass on the bad news */
                kfree(clip_vcc);
                return;
        }
        atm_return(vcc, skb->truesize);
        skb->dev = clip_vcc->entry ? clip_vcc->entry->neigh->dev : clip_devs;
        /* clip_vcc->entry == NULL if we don't have an IP address yet */
        if (!skb->dev) {
                dev_kfree_skb_any(skb);
                return;
        }
        ATM_SKB(skb)->vcc = vcc;
        skb_reset_mac_header(skb);
        if (!clip_vcc->encap ||
            skb->len < RFC1483LLC_LEN ||
            memcmp(skb->data, llc_oui, sizeof(llc_oui)))
                skb->protocol = htons(ETH_P_IP);
        else {
                skb->protocol = ((__be16 *)skb->data)[3];
                skb_pull(skb, RFC1483LLC_LEN);
                if (skb->protocol == htons(ETH_P_ARP)) {
                        skb->dev->stats.rx_packets++;
                        skb->dev->stats.rx_bytes += skb->len;
                        clip_arp_rcv(skb);
                        return;
                }
        }
        clip_vcc->last_use = jiffies;
        skb->dev->stats.rx_packets++;
        skb->dev->stats.rx_bytes += skb->len;
        memset(ATM_SKB(skb), 0, sizeof(struct atm_skb_data));
        netif_rx(skb);
}

/*
 * Note: these spinlocks _must_not_ block on non-SMP. The only goal is that
 * clip_pop is atomic with respect to the critical section in clip_start_xmit.
 */

static void clip_pop(struct atm_vcc *vcc, struct sk_buff *skb)
{
        struct clip_vcc *clip_vcc = CLIP_VCC(vcc);
        struct net_device *dev = skb->dev;
        int old;
        unsigned long flags;

        pr_debug("(vcc %p)\n", vcc);
        clip_vcc->old_pop(vcc, skb);
        /* skb->dev == NULL in outbound ARP packets */
        if (!dev)
                return;
        spin_lock_irqsave(&PRIV(dev)->xoff_lock, flags);
        if (atm_may_send(vcc, 0)) {
                old = xchg(&clip_vcc->xoff, 0);
                if (old)
                        netif_wake_queue(dev);
        }
        spin_unlock_irqrestore(&PRIV(dev)->xoff_lock, flags);
}

static void clip_neigh_solicit(struct neighbour *neigh, struct sk_buff *skb)
{
        __be32 *ip = (__be32 *) neigh->primary_key;

        pr_debug("(neigh %p, skb %p)\n", neigh, skb);
        to_atmarpd(act_need, PRIV(neigh->dev)->number, *ip);
}

static void clip_neigh_error(struct neighbour *neigh, struct sk_buff *skb)
{
#ifndef CONFIG_ATM_CLIP_NO_ICMP
        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0);
#endif
        kfree_skb(skb);
}

static const struct neigh_ops clip_neigh_ops = {
        .family =               AF_INET,
        .solicit =              clip_neigh_solicit,
        .error_report =         clip_neigh_error,
        .output =               neigh_direct_output,
        .connected_output =     neigh_direct_output,
};

static int clip_constructor(struct net_device *dev, struct neighbour *neigh)
{
        struct atmarp_entry *entry = neighbour_priv(neigh);

        if (neigh->tbl->family != AF_INET)
                return -EINVAL;

        if (neigh->type != RTN_UNICAST)
                return -EINVAL;

        neigh->nud_state = NUD_NONE;
        neigh->ops = &clip_neigh_ops;
        neigh->output = neigh->ops->output;
        entry->neigh = neigh;
        entry->vccs = NULL;
        entry->expires = jiffies - 1;

        return 0;
}

/* @@@ copy bh locking from arp.c -- need to bh-enable atm code before */

/*
 * We play with the resolve flag: 0 and 1 have the usual meaning, but -1 means
 * to allocate the neighbour entry but not to ask atmarpd for resolution. Also,
 * don't increment the usage count. This is used to create entries in
 * clip_setentry.
 */

static int clip_encap(struct atm_vcc *vcc, int mode)
{
        if (!CLIP_VCC(vcc))
                return -EBADFD;

        CLIP_VCC(vcc)->encap = mode;
        return 0;
}

static netdev_tx_t clip_start_xmit(struct sk_buff *skb,
                                   struct net_device *dev)
{
        struct clip_priv *clip_priv = PRIV(dev);
        struct dst_entry *dst = skb_dst(skb);
        struct atmarp_entry *entry;
        struct neighbour *n;
        struct atm_vcc *vcc;
        struct rtable *rt;
        __be32 *daddr;
        int old;
        unsigned long flags;

        pr_debug("(skb %p)\n", skb);
        if (!dst) {
                pr_err("skb_dst(skb) == NULL\n");
                dev_kfree_skb(skb);
                dev->stats.tx_dropped++;
                return NETDEV_TX_OK;
        }
        rt = (struct rtable *) dst;
        if (rt->rt_gw_family == AF_INET)
                daddr = &rt->rt_gw4;
        else
                daddr = &ip_hdr(skb)->daddr;
        n = dst_neigh_lookup(dst, daddr);
        if (!n) {
                pr_err("NO NEIGHBOUR !\n");
                dev_kfree_skb(skb);
                dev->stats.tx_dropped++;
                return NETDEV_TX_OK;
        }
        entry = neighbour_priv(n);
        if (!entry->vccs) {
                if (time_after(jiffies, entry->expires)) {
                        /* should be resolved */
                        entry->expires = jiffies + ATMARP_RETRY_DELAY * HZ;
                        to_atmarpd(act_need, PRIV(dev)->number, *((__be32 *)n->primary_key));
                }
                if (entry->neigh->arp_queue.qlen < ATMARP_MAX_UNRES_PACKETS)
                        skb_queue_tail(&entry->neigh->arp_queue, skb);
                else {
                        dev_kfree_skb(skb);
                        dev->stats.tx_dropped++;
                }
                goto out_release_neigh;
        }
        pr_debug("neigh %p, vccs %p\n", entry, entry->vccs);
        ATM_SKB(skb)->vcc = vcc = entry->vccs->vcc;
        pr_debug("using neighbour %p, vcc %p\n", n, vcc);
        if (entry->vccs->encap) {
                void *here;

                here = skb_push(skb, RFC1483LLC_LEN);
                memcpy(here, llc_oui, sizeof(llc_oui));
                ((__be16 *) here)[3] = skb->protocol;
        }
        atm_account_tx(vcc, skb);
        entry->vccs->last_use = jiffies;
        pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n", skb, vcc, vcc->dev);
        old = xchg(&entry->vccs->xoff, 1);      /* assume XOFF ... */
        if (old) {
                pr_warn("XOFF->XOFF transition\n");
                goto out_release_neigh;
        }
        dev->stats.tx_packets++;
        dev->stats.tx_bytes += skb->len;
        vcc->send(vcc, skb);
        if (atm_may_send(vcc, 0)) {
                entry->vccs->xoff = 0;
                goto out_release_neigh;
        }
        spin_lock_irqsave(&clip_priv->xoff_lock, flags);
        netif_stop_queue(dev);  /* XOFF -> throttle immediately */
        barrier();
        if (!entry->vccs->xoff)
                netif_start_queue(dev);
        /* Oh, we just raced with clip_pop. netif_start_queue should be
           good enough, because nothing should really be asleep because
           of the brief netif_stop_queue. If this isn't true or if it
           changes, use netif_wake_queue instead. */
        spin_unlock_irqrestore(&clip_priv->xoff_lock, flags);
out_release_neigh:
        neigh_release(n);
        return NETDEV_TX_OK;
}

static int clip_mkip(struct atm_vcc *vcc, int timeout)
{
        struct clip_vcc *clip_vcc;

        if (!vcc->push)
                return -EBADFD;
        clip_vcc = kmalloc(sizeof(struct clip_vcc), GFP_KERNEL);
        if (!clip_vcc)
                return -ENOMEM;
        pr_debug("%p vcc %p\n", clip_vcc, vcc);
        clip_vcc->vcc = vcc;
        vcc->user_back = clip_vcc;
        set_bit(ATM_VF_IS_CLIP, &vcc->flags);
        clip_vcc->entry = NULL;
        clip_vcc->xoff = 0;
        clip_vcc->encap = 1;
        clip_vcc->last_use = jiffies;
        clip_vcc->idle_timeout = timeout * HZ;
        clip_vcc->old_push = vcc->push;
        clip_vcc->old_pop = vcc->pop;
        vcc->push = clip_push;
        vcc->pop = clip_pop;

        /* re-process everything received between connection setup and MKIP */
        vcc_process_recv_queue(vcc);

        return 0;
}

static int clip_setentry(struct atm_vcc *vcc, __be32 ip)
{
        struct neighbour *neigh;
        struct atmarp_entry *entry;
        int error;
        struct clip_vcc *clip_vcc;
        struct rtable *rt;

        if (vcc->push != clip_push) {
                pr_warn("non-CLIP VCC\n");
                return -EBADF;
        }
        clip_vcc = CLIP_VCC(vcc);
        if (!ip) {
                if (!clip_vcc->entry) {
                        pr_err("hiding hidden ATMARP entry\n");
                        return 0;
                }
                pr_debug("remove\n");
                unlink_clip_vcc(clip_vcc);
                return 0;
        }
        rt = ip_route_output(&init_net, ip, 0, 1, 0);
        if (IS_ERR(rt))
                return PTR_ERR(rt);
        neigh = __neigh_lookup(&arp_tbl, &ip, rt->dst.dev, 1);
        ip_rt_put(rt);
        if (!neigh)
                return -ENOMEM;
        entry = neighbour_priv(neigh);
        if (entry != clip_vcc->entry) {
                if (!clip_vcc->entry)
                        pr_debug("add\n");
                else {
                        pr_debug("update\n");
                        unlink_clip_vcc(clip_vcc);
                }
                link_vcc(clip_vcc, entry);
        }
        error = neigh_update(neigh, llc_oui, NUD_PERMANENT,
                             NEIGH_UPDATE_F_OVERRIDE | NEIGH_UPDATE_F_ADMIN, 0);
        neigh_release(neigh);
        return error;
}

static const struct net_device_ops clip_netdev_ops = {
        .ndo_start_xmit         = clip_start_xmit,
        .ndo_neigh_construct    = clip_constructor,
};

static void clip_setup(struct net_device *dev)
{
        dev->netdev_ops = &clip_netdev_ops;
        dev->type = ARPHRD_ATM;
        dev->neigh_priv_len = sizeof(struct atmarp_entry);
        dev->hard_header_len = RFC1483LLC_LEN;
        dev->mtu = RFC1626_MTU;
        dev->tx_queue_len = 100;        /* "normal" queue (packets) */
        /* When using a "real" qdisc, the qdisc determines the queue */
        /* length. tx_queue_len is only used for the default case, */
        /* without any more elaborate queuing. 100 is a reasonable */
        /* compromise between decent burst-tolerance and protection */
        /* against memory hogs. */
        netif_keep_dst(dev);
}

static int clip_create(int number)
{
        struct net_device *dev;
        struct clip_priv *clip_priv;
        int error;

        if (number != -1) {
                for (dev = clip_devs; dev; dev = PRIV(dev)->next)
                        if (PRIV(dev)->number == number)
                                return -EEXIST;
        } else {
                number = 0;
                for (dev = clip_devs; dev; dev = PRIV(dev)->next)
                        if (PRIV(dev)->number >= number)
                                number = PRIV(dev)->number + 1;
        }
        dev = alloc_netdev(sizeof(struct clip_priv), "", NET_NAME_UNKNOWN,
                           clip_setup);
        if (!dev)
                return -ENOMEM;
        clip_priv = PRIV(dev);
        sprintf(dev->name, "atm%d", number);
        spin_lock_init(&clip_priv->xoff_lock);
        clip_priv->number = number;
        error = register_netdev(dev);
        if (error) {
                free_netdev(dev);
                return error;
        }
        clip_priv->next = clip_devs;
        clip_devs = dev;
        pr_debug("registered (net:%s)\n", dev->name);
        return number;
}

static int clip_device_event(struct notifier_block *this, unsigned long event,
                             void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);

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

        if (event == NETDEV_UNREGISTER)
                return NOTIFY_DONE;

        /* ignore non-CLIP devices */
        if (dev->type != ARPHRD_ATM || dev->netdev_ops != &clip_netdev_ops)
                return NOTIFY_DONE;

        switch (event) {
        case NETDEV_UP:
                pr_debug("NETDEV_UP\n");
                to_atmarpd(act_up, PRIV(dev)->number, 0);
                break;
        case NETDEV_GOING_DOWN:
                pr_debug("NETDEV_DOWN\n");
                to_atmarpd(act_down, PRIV(dev)->number, 0);
                break;
        case NETDEV_CHANGE:
        case NETDEV_CHANGEMTU:
                pr_debug("NETDEV_CHANGE*\n");
                to_atmarpd(act_change, PRIV(dev)->number, 0);
                break;
        }
        return NOTIFY_DONE;
}

static int clip_inet_event(struct notifier_block *this, unsigned long event,
                           void *ifa)
{
        struct in_device *in_dev;
        struct netdev_notifier_info info;

        in_dev = ((struct in_ifaddr *)ifa)->ifa_dev;
        /*
         * Transitions are of the down-change-up type, so it's sufficient to
         * handle the change on up.
         */
        if (event != NETDEV_UP)
                return NOTIFY_DONE;
        netdev_notifier_info_init(&info, in_dev->dev);
        return clip_device_event(this, NETDEV_CHANGE, &info);
}

static struct notifier_block clip_dev_notifier = {
        .notifier_call = clip_device_event,
};



static struct notifier_block clip_inet_notifier = {
        .notifier_call = clip_inet_event,
};



static void atmarpd_close(struct atm_vcc *vcc)
{
        pr_debug("\n");

        rtnl_lock();
        atmarpd = NULL;
        skb_queue_purge(&sk_atm(vcc)->sk_receive_queue);
        rtnl_unlock();

        pr_debug("(done)\n");
        module_put(THIS_MODULE);
}

static const struct atmdev_ops atmarpd_dev_ops = {
        .close = atmarpd_close
};


static struct atm_dev atmarpd_dev = {
        .ops =                  &atmarpd_dev_ops,
        .type =                 "arpd",
        .number =               999,
        .lock =                 __SPIN_LOCK_UNLOCKED(atmarpd_dev.lock)
};


static int atm_init_atmarp(struct atm_vcc *vcc)
{
        rtnl_lock();
        if (atmarpd) {
                rtnl_unlock();
                return -EADDRINUSE;
        }

        mod_timer(&idle_timer, jiffies + CLIP_CHECK_INTERVAL * HZ);

        atmarpd = vcc;
        set_bit(ATM_VF_META, &vcc->flags);
        set_bit(ATM_VF_READY, &vcc->flags);
            /* allow replies and avoid getting closed if signaling dies */
        vcc->dev = &atmarpd_dev;
        vcc_insert_socket(sk_atm(vcc));
        vcc->push = NULL;
        vcc->pop = NULL; /* crash */
        vcc->push_oam = NULL; /* crash */
        rtnl_unlock();
        return 0;
}

static int clip_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
{
        struct atm_vcc *vcc = ATM_SD(sock);
        int err = 0;

        switch (cmd) {
        case SIOCMKCLIP:
        case ATMARPD_CTRL:
        case ATMARP_MKIP:
        case ATMARP_SETENTRY:
        case ATMARP_ENCAP:
                if (!capable(CAP_NET_ADMIN))
                        return -EPERM;
                break;
        default:
                return -ENOIOCTLCMD;
        }

        switch (cmd) {
        case SIOCMKCLIP:
                err = clip_create(arg);
                break;
        case ATMARPD_CTRL:
                err = atm_init_atmarp(vcc);
                if (!err) {
                        sock->state = SS_CONNECTED;
                        __module_get(THIS_MODULE);
                }
                break;
        case ATMARP_MKIP:
                err = clip_mkip(vcc, arg);
                break;
        case ATMARP_SETENTRY:
                err = clip_setentry(vcc, (__force __be32)arg);
                break;
        case ATMARP_ENCAP:
                err = clip_encap(vcc, arg);
                break;
        }
        return err;
}

static struct atm_ioctl clip_ioctl_ops = {
        .owner = THIS_MODULE,
        .ioctl = clip_ioctl,
};

#ifdef CONFIG_PROC_FS

static void svc_addr(struct seq_file *seq, struct sockaddr_atmsvc *addr)
{
        static int code[] = { 1, 2, 10, 6, 1, 0 };
        static int e164[] = { 1, 8, 4, 6, 1, 0 };

        if (*addr->sas_addr.pub) {
                seq_printf(seq, "%s", addr->sas_addr.pub);
                if (*addr->sas_addr.prv)
                        seq_putc(seq, '+');
        } else if (!*addr->sas_addr.prv) {
                seq_printf(seq, "%s", "(none)");
                return;
        }
        if (*addr->sas_addr.prv) {
                unsigned char *prv = addr->sas_addr.prv;
                int *fields;
                int i, j;

                fields = *prv == ATM_AFI_E164 ? e164 : code;
                for (i = 0; fields[i]; i++) {
                        for (j = fields[i]; j; j--)
                                seq_printf(seq, "%02X", *prv++);
                        if (fields[i + 1])
                                seq_putc(seq, '.');
                }
        }
}

/* This means the neighbour entry has no attached VCC objects. */
#define SEQ_NO_VCC_TOKEN        ((void *) 2)

static void atmarp_info(struct seq_file *seq, struct neighbour *n,
                        struct atmarp_entry *entry, struct clip_vcc *clip_vcc)
{
        struct net_device *dev = n->dev;
        unsigned long exp;
        char buf[17];
        int svc, llc, off;

        svc = ((clip_vcc == SEQ_NO_VCC_TOKEN) ||
               (sk_atm(clip_vcc->vcc)->sk_family == AF_ATMSVC));

        llc = ((clip_vcc == SEQ_NO_VCC_TOKEN) || clip_vcc->encap);

        if (clip_vcc == SEQ_NO_VCC_TOKEN)
                exp = entry->neigh->used;
        else
                exp = clip_vcc->last_use;

        exp = (jiffies - exp) / HZ;

        seq_printf(seq, "%-6s%-4s%-4s%5ld ",
                   dev->name, svc ? "SVC" : "PVC", llc ? "LLC" : "NULL", exp);

        off = scnprintf(buf, sizeof(buf) - 1, "%pI4", n->primary_key);
        while (off < 16)
                buf[off++] = ' ';
        buf[off] = '\0';
        seq_printf(seq, "%s", buf);

        if (clip_vcc == SEQ_NO_VCC_TOKEN) {
                if (time_before(jiffies, entry->expires))
                        seq_printf(seq, "(resolving)\n");
                else
                        seq_printf(seq, "(expired, ref %d)\n",
                                   refcount_read(&entry->neigh->refcnt));
        } else if (!svc) {
                seq_printf(seq, "%d.%d.%d\n",
                           clip_vcc->vcc->dev->number,
                           clip_vcc->vcc->vpi, clip_vcc->vcc->vci);
        } else {
                svc_addr(seq, &clip_vcc->vcc->remote);
                seq_putc(seq, '\n');
        }
}

struct clip_seq_state {
        /* This member must be first. */
        struct neigh_seq_state ns;

        /* Local to clip specific iteration. */
        struct clip_vcc *vcc;
};

static struct clip_vcc *clip_seq_next_vcc(struct atmarp_entry *e,
                                          struct clip_vcc *curr)
{
        if (!curr) {
                curr = e->vccs;
                if (!curr)
                        return SEQ_NO_VCC_TOKEN;
                return curr;
        }
        if (curr == SEQ_NO_VCC_TOKEN)
                return NULL;

        curr = curr->next;

        return curr;
}

static void *clip_seq_vcc_walk(struct clip_seq_state *state,
                               struct atmarp_entry *e, loff_t * pos)
{
        struct clip_vcc *vcc = state->vcc;

        vcc = clip_seq_next_vcc(e, vcc);
        if (vcc && pos != NULL) {
                while (*pos) {
                        vcc = clip_seq_next_vcc(e, vcc);
                        if (!vcc)
                                break;
                        --(*pos);
                }
        }
        state->vcc = vcc;

        return vcc;
}

static void *clip_seq_sub_iter(struct neigh_seq_state *_state,
                               struct neighbour *n, loff_t * pos)
{
        struct clip_seq_state *state = (struct clip_seq_state *)_state;

        if (n->dev->type != ARPHRD_ATM)
                return NULL;

        return clip_seq_vcc_walk(state, neighbour_priv(n), pos);
}

static void *clip_seq_start(struct seq_file *seq, loff_t * pos)
{
        struct clip_seq_state *state = seq->private;
        state->ns.neigh_sub_iter = clip_seq_sub_iter;
        return neigh_seq_start(seq, pos, &arp_tbl, NEIGH_SEQ_NEIGH_ONLY);
}

static int clip_seq_show(struct seq_file *seq, void *v)
{
        static char atm_arp_banner[] =
            "IPitf TypeEncp Idle IP address      ATM address\n";

        if (v == SEQ_START_TOKEN) {
                seq_puts(seq, atm_arp_banner);
        } else {
                struct clip_seq_state *state = seq->private;
                struct clip_vcc *vcc = state->vcc;
                struct neighbour *n = v;

                atmarp_info(seq, n, neighbour_priv(n), vcc);
        }
        return 0;
}

static const struct seq_operations arp_seq_ops = {
        .start  = clip_seq_start,
        .next   = neigh_seq_next,
        .stop   = neigh_seq_stop,
        .show   = clip_seq_show,
};
#endif

static void atm_clip_exit_noproc(void);

static int __init atm_clip_init(void)
{
        register_atm_ioctl(&clip_ioctl_ops);
        register_netdevice_notifier(&clip_dev_notifier);
        register_inetaddr_notifier(&clip_inet_notifier);

        timer_setup(&idle_timer, idle_timer_check, 0);

#ifdef CONFIG_PROC_FS
        {
                struct proc_dir_entry *p;

                p = proc_create_net("arp", 0444, atm_proc_root, &arp_seq_ops,
                                sizeof(struct clip_seq_state));
                if (!p) {
                        pr_err("Unable to initialize /proc/net/atm/arp\n");
                        atm_clip_exit_noproc();
                        return -ENOMEM;
                }
        }
#endif

        return 0;
}

static void atm_clip_exit_noproc(void)
{
        struct net_device *dev, *next;

        unregister_inetaddr_notifier(&clip_inet_notifier);
        unregister_netdevice_notifier(&clip_dev_notifier);

        deregister_atm_ioctl(&clip_ioctl_ops);

        /* First, stop the idle timer, so it stops banging
         * on the table.
         */
        del_timer_sync(&idle_timer);

        dev = clip_devs;
        while (dev) {
                next = PRIV(dev)->next;
                unregister_netdev(dev);
                free_netdev(dev);
                dev = next;
        }
}

static void __exit atm_clip_exit(void)
{
        remove_proc_entry("arp", atm_proc_root);

        atm_clip_exit_noproc();
}

module_init(atm_clip_init);
module_exit(atm_clip_exit);
MODULE_AUTHOR("Werner Almesberger");
MODULE_DESCRIPTION("Classical/IP over ATM interface");
MODULE_LICENSE("GPL");