// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      AARP:           An implementation of the AppleTalk AARP protocol for
 *                      Ethernet 'ELAP'.
 *
 *              Alan Cox  <Alan.Cox@linux.org>
 *
 *      This doesn't fit cleanly with the IP arp. Potentially we can use
 *      the generic neighbour discovery code to clean this up.
 *
 *      FIXME:
 *              We ought to handle the retransmits with a single list and a
 *      separate fast timer for when it is needed.
 *              Use neighbour discovery code.
 *              Token Ring Support.
 *
 *      References:
 *              Inside AppleTalk (2nd Ed).
 *      Fixes:
 *              Jaume Grau      -       flush caches on AARP_PROBE
 *              Rob Newberry    -       Added proxy AARP and AARP proc fs,
 *                                      moved probing from DDP module.
 *              Arnaldo C. Melo -       don't mangle rx packets
 */

#include <linux/if_arp.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <net/datalink.h>
#include <net/psnap.h>
#include <linux/atalk.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/export.h>
#include <linux/etherdevice.h>

int sysctl_aarp_expiry_time = AARP_EXPIRY_TIME;
int sysctl_aarp_tick_time = AARP_TICK_TIME;
int sysctl_aarp_retransmit_limit = AARP_RETRANSMIT_LIMIT;
int sysctl_aarp_resolve_time = AARP_RESOLVE_TIME;

/* Lists of aarp entries */
/**
 *      struct aarp_entry - AARP entry
 *      @last_sent - Last time we xmitted the aarp request
 *      @packet_queue - Queue of frames wait for resolution
 *      @status - Used for proxy AARP
 *      expires_at - Entry expiry time
 *      target_addr - DDP Address
 *      dev - Device to use
 *      hwaddr - Physical i/f address of target/router
 *      xmit_count - When this hits 10 we give up
 *      next - Next entry in chain
 */
struct aarp_entry {
        /* These first two are only used for unresolved entries */
        unsigned long           last_sent;
        struct sk_buff_head     packet_queue;
        int                     status;
        unsigned long           expires_at;
        struct atalk_addr       target_addr;
        struct net_device       *dev;
        char                    hwaddr[ETH_ALEN];
        unsigned short          xmit_count;
        struct aarp_entry       *next;
};

/* Hashed list of resolved, unresolved and proxy entries */
static struct aarp_entry *resolved[AARP_HASH_SIZE];
static struct aarp_entry *unresolved[AARP_HASH_SIZE];
static struct aarp_entry *proxies[AARP_HASH_SIZE];
static int unresolved_count;

/* One lock protects it all. */
static DEFINE_RWLOCK(aarp_lock);

/* Used to walk the list and purge/kick entries.  */
static struct timer_list aarp_timer;

/*
 *      Delete an aarp queue
 *
 *      Must run under aarp_lock.
 */
static void __aarp_expire(struct aarp_entry *a)
{
        skb_queue_purge(&a->packet_queue);
        kfree(a);
}

/*
 *      Send an aarp queue entry request
 *
 *      Must run under aarp_lock.
 */
static void __aarp_send_query(struct aarp_entry *a)
{
        static unsigned char aarp_eth_multicast[ETH_ALEN] =
                                        { 0x09, 0x00, 0x07, 0xFF, 0xFF, 0xFF };
        struct net_device *dev = a->dev;
        struct elapaarp *eah;
        int len = dev->hard_header_len + sizeof(*eah) + aarp_dl->header_length;
        struct sk_buff *skb = alloc_skb(len, GFP_ATOMIC);
        struct atalk_addr *sat = atalk_find_dev_addr(dev);

        if (!skb)
                return;

        if (!sat) {
                kfree_skb(skb);
                return;
        }

        /* Set up the buffer */
        skb_reserve(skb, dev->hard_header_len + aarp_dl->header_length);
        skb_reset_network_header(skb);
        skb_reset_transport_header(skb);
        skb_put(skb, sizeof(*eah));
        skb->protocol    = htons(ETH_P_ATALK);
        skb->dev         = dev;
        eah              = aarp_hdr(skb);

        /* Set up the ARP */
        eah->hw_type     = htons(AARP_HW_TYPE_ETHERNET);
        eah->pa_type     = htons(ETH_P_ATALK);
        eah->hw_len      = ETH_ALEN;
        eah->pa_len      = AARP_PA_ALEN;
        eah->function    = htons(AARP_REQUEST);

        ether_addr_copy(eah->hw_src, dev->dev_addr);

        eah->pa_src_zero = 0;
        eah->pa_src_net  = sat->s_net;
        eah->pa_src_node = sat->s_node;

        eth_zero_addr(eah->hw_dst);

        eah->pa_dst_zero = 0;
        eah->pa_dst_net  = a->target_addr.s_net;
        eah->pa_dst_node = a->target_addr.s_node;

        /* Send it */
        aarp_dl->request(aarp_dl, skb, aarp_eth_multicast);
        /* Update the sending count */
        a->xmit_count++;
        a->last_sent = jiffies;
}

/* This runs under aarp_lock and in softint context, so only atomic memory
 * allocations can be used. */
static void aarp_send_reply(struct net_device *dev, struct atalk_addr *us,
                            struct atalk_addr *them, unsigned char *sha)
{
        struct elapaarp *eah;
        int len = dev->hard_header_len + sizeof(*eah) + aarp_dl->header_length;
        struct sk_buff *skb = alloc_skb(len, GFP_ATOMIC);

        if (!skb)
                return;

        /* Set up the buffer */
        skb_reserve(skb, dev->hard_header_len + aarp_dl->header_length);
        skb_reset_network_header(skb);
        skb_reset_transport_header(skb);
        skb_put(skb, sizeof(*eah));
        skb->protocol    = htons(ETH_P_ATALK);
        skb->dev         = dev;
        eah              = aarp_hdr(skb);

        /* Set up the ARP */
        eah->hw_type     = htons(AARP_HW_TYPE_ETHERNET);
        eah->pa_type     = htons(ETH_P_ATALK);
        eah->hw_len      = ETH_ALEN;
        eah->pa_len      = AARP_PA_ALEN;
        eah->function    = htons(AARP_REPLY);

        ether_addr_copy(eah->hw_src, dev->dev_addr);

        eah->pa_src_zero = 0;
        eah->pa_src_net  = us->s_net;
        eah->pa_src_node = us->s_node;

        if (!sha)
                eth_zero_addr(eah->hw_dst);
        else
                ether_addr_copy(eah->hw_dst, sha);

        eah->pa_dst_zero = 0;
        eah->pa_dst_net  = them->s_net;
        eah->pa_dst_node = them->s_node;

        /* Send it */
        aarp_dl->request(aarp_dl, skb, sha);
}

/*
 *      Send probe frames. Called from aarp_probe_network and
 *      aarp_proxy_probe_network.
 */

static void aarp_send_probe(struct net_device *dev, struct atalk_addr *us)
{
        struct elapaarp *eah;
        int len = dev->hard_header_len + sizeof(*eah) + aarp_dl->header_length;
        struct sk_buff *skb = alloc_skb(len, GFP_ATOMIC);
        static unsigned char aarp_eth_multicast[ETH_ALEN] =
                                        { 0x09, 0x00, 0x07, 0xFF, 0xFF, 0xFF };

        if (!skb)
                return;

        /* Set up the buffer */
        skb_reserve(skb, dev->hard_header_len + aarp_dl->header_length);
        skb_reset_network_header(skb);
        skb_reset_transport_header(skb);
        skb_put(skb, sizeof(*eah));
        skb->protocol    = htons(ETH_P_ATALK);
        skb->dev         = dev;
        eah              = aarp_hdr(skb);

        /* Set up the ARP */
        eah->hw_type     = htons(AARP_HW_TYPE_ETHERNET);
        eah->pa_type     = htons(ETH_P_ATALK);
        eah->hw_len      = ETH_ALEN;
        eah->pa_len      = AARP_PA_ALEN;
        eah->function    = htons(AARP_PROBE);

        ether_addr_copy(eah->hw_src, dev->dev_addr);

        eah->pa_src_zero = 0;
        eah->pa_src_net  = us->s_net;
        eah->pa_src_node = us->s_node;

        eth_zero_addr(eah->hw_dst);

        eah->pa_dst_zero = 0;
        eah->pa_dst_net  = us->s_net;
        eah->pa_dst_node = us->s_node;

        /* Send it */
        aarp_dl->request(aarp_dl, skb, aarp_eth_multicast);
}

/*
 *      Handle an aarp timer expire
 *
 *      Must run under the aarp_lock.
 */

static void __aarp_expire_timer(struct aarp_entry **n)
{
        struct aarp_entry *t;

        while (*n)
                /* Expired ? */
                if (time_after(jiffies, (*n)->expires_at)) {
                        t = *n;
                        *n = (*n)->next;
                        __aarp_expire(t);
                } else
                        n = &((*n)->next);
}

/*
 *      Kick all pending requests 5 times a second.
 *
 *      Must run under the aarp_lock.
 */
static void __aarp_kick(struct aarp_entry **n)
{
        struct aarp_entry *t;

        while (*n)
                /* Expired: if this will be the 11th tx, we delete instead. */
                if ((*n)->xmit_count >= sysctl_aarp_retransmit_limit) {
                        t = *n;
                        *n = (*n)->next;
                        __aarp_expire(t);
                } else {
                        __aarp_send_query(*n);
                        n = &((*n)->next);
                }
}

/*
 *      A device has gone down. Take all entries referring to the device
 *      and remove them.
 *
 *      Must run under the aarp_lock.
 */
static void __aarp_expire_device(struct aarp_entry **n, struct net_device *dev)
{
        struct aarp_entry *t;

        while (*n)
                if ((*n)->dev == dev) {
                        t = *n;
                        *n = (*n)->next;
                        __aarp_expire(t);
                } else
                        n = &((*n)->next);
}

/* Handle the timer event */
static void aarp_expire_timeout(struct timer_list *unused)
{
        int ct;

        write_lock_bh(&aarp_lock);

        for (ct = 0; ct < AARP_HASH_SIZE; ct++) {
                __aarp_expire_timer(&resolved[ct]);
                __aarp_kick(&unresolved[ct]);
                __aarp_expire_timer(&unresolved[ct]);
                __aarp_expire_timer(&proxies[ct]);
        }

        write_unlock_bh(&aarp_lock);
        mod_timer(&aarp_timer, jiffies +
                               (unresolved_count ? sysctl_aarp_tick_time :
                                sysctl_aarp_expiry_time));
}

/* Network device notifier chain handler. */
static int aarp_device_event(struct notifier_block *this, unsigned long event,
                             void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);
        int ct;

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

        if (event == NETDEV_DOWN) {
                write_lock_bh(&aarp_lock);

                for (ct = 0; ct < AARP_HASH_SIZE; ct++) {
                        __aarp_expire_device(&resolved[ct], dev);
                        __aarp_expire_device(&unresolved[ct], dev);
                        __aarp_expire_device(&proxies[ct], dev);
                }

                write_unlock_bh(&aarp_lock);
        }
        return NOTIFY_DONE;
}

/* Expire all entries in a hash chain */
static void __aarp_expire_all(struct aarp_entry **n)
{
        struct aarp_entry *t;

        while (*n) {
                t = *n;
                *n = (*n)->next;
                __aarp_expire(t);
        }
}

/* Cleanup all hash chains -- module unloading */
static void aarp_purge(void)
{
        int ct;

        write_lock_bh(&aarp_lock);
        for (ct = 0; ct < AARP_HASH_SIZE; ct++) {
                __aarp_expire_all(&resolved[ct]);
                __aarp_expire_all(&unresolved[ct]);
                __aarp_expire_all(&proxies[ct]);
        }
        write_unlock_bh(&aarp_lock);
}

/*
 *      Create a new aarp entry.  This must use GFP_ATOMIC because it
 *      runs while holding spinlocks.
 */
static struct aarp_entry *aarp_alloc(void)
{
        struct aarp_entry *a = kmalloc(sizeof(*a), GFP_ATOMIC);

        if (a)
                skb_queue_head_init(&a->packet_queue);
        return a;
}

/*
 * Find an entry. We might return an expired but not yet purged entry. We
 * don't care as it will do no harm.
 *
 * This must run under the aarp_lock.
 */
static struct aarp_entry *__aarp_find_entry(struct aarp_entry *list,
                                            struct net_device *dev,
                                            struct atalk_addr *sat)
{
        while (list) {
                if (list->target_addr.s_net == sat->s_net &&
                    list->target_addr.s_node == sat->s_node &&
                    list->dev == dev)
                        break;
                list = list->next;
        }

        return list;
}

/* Called from the DDP code, and thus must be exported. */
void aarp_proxy_remove(struct net_device *dev, struct atalk_addr *sa)
{
        int hash = sa->s_node % (AARP_HASH_SIZE - 1);
        struct aarp_entry *a;

        write_lock_bh(&aarp_lock);

        a = __aarp_find_entry(proxies[hash], dev, sa);
        if (a)
                a->expires_at = jiffies - 1;

        write_unlock_bh(&aarp_lock);
}

/* This must run under aarp_lock. */
static struct atalk_addr *__aarp_proxy_find(struct net_device *dev,
                                            struct atalk_addr *sa)
{
        int hash = sa->s_node % (AARP_HASH_SIZE - 1);
        struct aarp_entry *a = __aarp_find_entry(proxies[hash], dev, sa);

        return a ? sa : NULL;
}

/*
 * Probe a Phase 1 device or a device that requires its Net:Node to
 * be set via an ioctl.
 */
static void aarp_send_probe_phase1(struct atalk_iface *iface)
{
        struct ifreq atreq;
        struct sockaddr_at *sa = (struct sockaddr_at *)&atreq.ifr_addr;
        const struct net_device_ops *ops = iface->dev->netdev_ops;

        sa->sat_addr.s_node = iface->address.s_node;
        sa->sat_addr.s_net = ntohs(iface->address.s_net);

        /* We pass the Net:Node to the drivers/cards by a Device ioctl. */
        if (!(ops->ndo_do_ioctl(iface->dev, &atreq, SIOCSIFADDR))) {
                ops->ndo_do_ioctl(iface->dev, &atreq, SIOCGIFADDR);
                if (iface->address.s_net != htons(sa->sat_addr.s_net) ||
                    iface->address.s_node != sa->sat_addr.s_node)
                        iface->status |= ATIF_PROBE_FAIL;

                iface->address.s_net  = htons(sa->sat_addr.s_net);
                iface->address.s_node = sa->sat_addr.s_node;
        }
}


void aarp_probe_network(struct atalk_iface *atif)
{
        if (atif->dev->type == ARPHRD_LOCALTLK ||
            atif->dev->type == ARPHRD_PPP)
                aarp_send_probe_phase1(atif);
        else {
                unsigned int count;

                for (count = 0; count < AARP_RETRANSMIT_LIMIT; count++) {
                        aarp_send_probe(atif->dev, &atif->address);

                        /* Defer 1/10th */
                        msleep(100);

                        if (atif->status & ATIF_PROBE_FAIL)
                                break;
                }
        }
}

int aarp_proxy_probe_network(struct atalk_iface *atif, struct atalk_addr *sa)
{
        int hash, retval = -EPROTONOSUPPORT;
        struct aarp_entry *entry;
        unsigned int count;

        /*
         * we don't currently support LocalTalk or PPP for proxy AARP;
         * if someone wants to try and add it, have fun
         */
        if (atif->dev->type == ARPHRD_LOCALTLK ||
            atif->dev->type == ARPHRD_PPP)
                goto out;

        /*
         * create a new AARP entry with the flags set to be published --
         * we need this one to hang around even if it's in use
         */
        entry = aarp_alloc();
        retval = -ENOMEM;
        if (!entry)
                goto out;

        entry->expires_at = -1;
        entry->status = ATIF_PROBE;
        entry->target_addr.s_node = sa->s_node;
        entry->target_addr.s_net = sa->s_net;
        entry->dev = atif->dev;

        write_lock_bh(&aarp_lock);

        hash = sa->s_node % (AARP_HASH_SIZE - 1);
        entry->next = proxies[hash];
        proxies[hash] = entry;

        for (count = 0; count < AARP_RETRANSMIT_LIMIT; count++) {
                aarp_send_probe(atif->dev, sa);

                /* Defer 1/10th */
                write_unlock_bh(&aarp_lock);
                msleep(100);
                write_lock_bh(&aarp_lock);

                if (entry->status & ATIF_PROBE_FAIL)
                        break;
        }

        if (entry->status & ATIF_PROBE_FAIL) {
                entry->expires_at = jiffies - 1; /* free the entry */
                retval = -EADDRINUSE; /* return network full */
        } else { /* clear the probing flag */
                entry->status &= ~ATIF_PROBE;
                retval = 1;
        }

        write_unlock_bh(&aarp_lock);
out:
        return retval;
}

/* Send a DDP frame */
int aarp_send_ddp(struct net_device *dev, struct sk_buff *skb,
                  struct atalk_addr *sa, void *hwaddr)
{
        static char ddp_eth_multicast[ETH_ALEN] =
                { 0x09, 0x00, 0x07, 0xFF, 0xFF, 0xFF };
        int hash;
        struct aarp_entry *a;

        skb_reset_network_header(skb);

        /* Check for LocalTalk first */
        if (dev->type == ARPHRD_LOCALTLK) {
                struct atalk_addr *at = atalk_find_dev_addr(dev);
                struct ddpehdr *ddp = (struct ddpehdr *)skb->data;
                int ft = 2;

                /*
                 * Compressible ?
                 *
                 * IFF: src_net == dest_net == device_net
                 * (zero matches anything)
                 */

                if ((!ddp->deh_snet || at->s_net == ddp->deh_snet) &&
                    (!ddp->deh_dnet || at->s_net == ddp->deh_dnet)) {
                        skb_pull(skb, sizeof(*ddp) - 4);

                        /*
                         *      The upper two remaining bytes are the port
                         *      numbers we just happen to need. Now put the
                         *      length in the lower two.
                         */
                        *((__be16 *)skb->data) = htons(skb->len);
                        ft = 1;
                }
                /*
                 * Nice and easy. No AARP type protocols occur here so we can
                 * just shovel it out with a 3 byte LLAP header
                 */

                skb_push(skb, 3);
                skb->data[0] = sa->s_node;
                skb->data[1] = at->s_node;
                skb->data[2] = ft;
                skb->dev     = dev;
                goto sendit;
        }

        /* On a PPP link we neither compress nor aarp.  */
        if (dev->type == ARPHRD_PPP) {
                skb->protocol = htons(ETH_P_PPPTALK);
                skb->dev = dev;
                goto sendit;
        }

        /* Non ELAP we cannot do. */
        if (dev->type != ARPHRD_ETHER)
                goto free_it;

        skb->dev = dev;
        skb->protocol = htons(ETH_P_ATALK);
        hash = sa->s_node % (AARP_HASH_SIZE - 1);

        /* Do we have a resolved entry? */
        if (sa->s_node == ATADDR_BCAST) {
                /* Send it */
                ddp_dl->request(ddp_dl, skb, ddp_eth_multicast);
                goto sent;
        }

        write_lock_bh(&aarp_lock);
        a = __aarp_find_entry(resolved[hash], dev, sa);

        if (a) { /* Return 1 and fill in the address */
                a->expires_at = jiffies + (sysctl_aarp_expiry_time * 10);
                ddp_dl->request(ddp_dl, skb, a->hwaddr);
                write_unlock_bh(&aarp_lock);
                goto sent;
        }

        /* Do we have an unresolved entry: This is the less common path */
        a = __aarp_find_entry(unresolved[hash], dev, sa);
        if (a) { /* Queue onto the unresolved queue */
                skb_queue_tail(&a->packet_queue, skb);
                goto out_unlock;
        }

        /* Allocate a new entry */
        a = aarp_alloc();
        if (!a) {
                /* Whoops slipped... good job it's an unreliable protocol 8) */
                write_unlock_bh(&aarp_lock);
                goto free_it;
        }

        /* Set up the queue */
        skb_queue_tail(&a->packet_queue, skb);
        a->expires_at    = jiffies + sysctl_aarp_resolve_time;
        a->dev           = dev;
        a->next          = unresolved[hash];
        a->target_addr   = *sa;
        a->xmit_count    = 0;
        unresolved[hash] = a;
        unresolved_count++;

        /* Send an initial request for the address */
        __aarp_send_query(a);

        /*
         * Switch to fast timer if needed (That is if this is the first
         * unresolved entry to get added)
         */

        if (unresolved_count == 1)
                mod_timer(&aarp_timer, jiffies + sysctl_aarp_tick_time);

        /* Now finally, it is safe to drop the lock. */
out_unlock:
        write_unlock_bh(&aarp_lock);

        /* Tell the ddp layer we have taken over for this frame. */
        goto sent;

sendit:
        if (skb->sk)
                skb->priority = skb->sk->sk_priority;
        if (dev_queue_xmit(skb))
                goto drop;
sent:
        return NET_XMIT_SUCCESS;
free_it:
        kfree_skb(skb);
drop:
        return NET_XMIT_DROP;
}
EXPORT_SYMBOL(aarp_send_ddp);

/*
 *      An entry in the aarp unresolved queue has become resolved. Send
 *      all the frames queued under it.
 *
 *      Must run under aarp_lock.
 */
static void __aarp_resolved(struct aarp_entry **list, struct aarp_entry *a,
                            int hash)
{
        struct sk_buff *skb;

        while (*list)
                if (*list == a) {
                        unresolved_count--;
                        *list = a->next;

                        /* Move into the resolved list */
                        a->next = resolved[hash];
                        resolved[hash] = a;

                        /* Kick frames off */
                        while ((skb = skb_dequeue(&a->packet_queue)) != NULL) {
                                a->expires_at = jiffies +
                                                sysctl_aarp_expiry_time * 10;
                                ddp_dl->request(ddp_dl, skb, a->hwaddr);
                        }
                } else
                        list = &((*list)->next);
}

/*
 *      This is called by the SNAP driver whenever we see an AARP SNAP
 *      frame. We currently only support Ethernet.
 */
static int aarp_rcv(struct sk_buff *skb, struct net_device *dev,
                    struct packet_type *pt, struct net_device *orig_dev)
{
        struct elapaarp *ea = aarp_hdr(skb);
        int hash, ret = 0;
        __u16 function;
        struct aarp_entry *a;
        struct atalk_addr sa, *ma, da;
        struct atalk_iface *ifa;

        if (!net_eq(dev_net(dev), &init_net))
                goto out0;

        /* We only do Ethernet SNAP AARP. */
        if (dev->type != ARPHRD_ETHER)
                goto out0;

        /* Frame size ok? */
        if (!skb_pull(skb, sizeof(*ea)))
                goto out0;

        function = ntohs(ea->function);

        /* Sanity check fields. */
        if (function < AARP_REQUEST || function > AARP_PROBE ||
            ea->hw_len != ETH_ALEN || ea->pa_len != AARP_PA_ALEN ||
            ea->pa_src_zero || ea->pa_dst_zero)
                goto out0;

        /* Looks good. */
        hash = ea->pa_src_node % (AARP_HASH_SIZE - 1);

        /* Build an address. */
        sa.s_node = ea->pa_src_node;
        sa.s_net = ea->pa_src_net;

        /* Process the packet. Check for replies of me. */
        ifa = atalk_find_dev(dev);
        if (!ifa)
                goto out1;

        if (ifa->status & ATIF_PROBE &&
            ifa->address.s_node == ea->pa_dst_node &&
            ifa->address.s_net == ea->pa_dst_net) {
                ifa->status |= ATIF_PROBE_FAIL; /* Fail the probe (in use) */
                goto out1;
        }

        /* Check for replies of proxy AARP entries */
        da.s_node = ea->pa_dst_node;
        da.s_net  = ea->pa_dst_net;

        write_lock_bh(&aarp_lock);
        a = __aarp_find_entry(proxies[hash], dev, &da);

        if (a && a->status & ATIF_PROBE) {
                a->status |= ATIF_PROBE_FAIL;
                /*
                 * we do not respond to probe or request packets for
                 * this address while we are probing this address
                 */
                goto unlock;
        }

        switch (function) {
        case AARP_REPLY:
                if (!unresolved_count)  /* Speed up */
                        break;

                /* Find the entry.  */
                a = __aarp_find_entry(unresolved[hash], dev, &sa);
                if (!a || dev != a->dev)
                        break;

                /* We can fill one in - this is good. */
                ether_addr_copy(a->hwaddr, ea->hw_src);
                __aarp_resolved(&unresolved[hash], a, hash);
                if (!unresolved_count)
                        mod_timer(&aarp_timer,
                                  jiffies + sysctl_aarp_expiry_time);
                break;

        case AARP_REQUEST:
        case AARP_PROBE:

                /*
                 * If it is my address set ma to my address and reply.
                 * We can treat probe and request the same.  Probe
                 * simply means we shouldn't cache the querying host,
                 * as in a probe they are proposing an address not
                 * using one.
                 *
                 * Support for proxy-AARP added. We check if the
                 * address is one of our proxies before we toss the
                 * packet out.
                 */

                sa.s_node = ea->pa_dst_node;
                sa.s_net  = ea->pa_dst_net;

                /* See if we have a matching proxy. */
                ma = __aarp_proxy_find(dev, &sa);
                if (!ma)
                        ma = &ifa->address;
                else { /* We need to make a copy of the entry. */
                        da.s_node = sa.s_node;
                        da.s_net = sa.s_net;
                        ma = &da;
                }

                if (function == AARP_PROBE) {
                        /*
                         * A probe implies someone trying to get an
                         * address. So as a precaution flush any
                         * entries we have for this address.
                         */
                        a = __aarp_find_entry(resolved[sa.s_node %
                                                       (AARP_HASH_SIZE - 1)],
                                              skb->dev, &sa);

                        /*
                         * Make it expire next tick - that avoids us
                         * getting into a probe/flush/learn/probe/
                         * flush/learn cycle during probing of a slow
                         * to respond host addr.
                         */
                        if (a) {
                                a->expires_at = jiffies - 1;
                                mod_timer(&aarp_timer, jiffies +
                                          sysctl_aarp_tick_time);
                        }
                }

                if (sa.s_node != ma->s_node)
                        break;

                if (sa.s_net && ma->s_net && sa.s_net != ma->s_net)
                        break;

                sa.s_node = ea->pa_src_node;
                sa.s_net = ea->pa_src_net;

                /* aarp_my_address has found the address to use for us.
                 */
                aarp_send_reply(dev, ma, &sa, ea->hw_src);
                break;
        }

unlock:
        write_unlock_bh(&aarp_lock);
out1:
        ret = 1;
out0:
        kfree_skb(skb);
        return ret;
}

static struct notifier_block aarp_notifier = {
        .notifier_call = aarp_device_event,
};

static unsigned char aarp_snap_id[] = { 0x00, 0x00, 0x00, 0x80, 0xF3 };

int __init aarp_proto_init(void)
{
        int rc;

        aarp_dl = register_snap_client(aarp_snap_id, aarp_rcv);
        if (!aarp_dl) {
                printk(KERN_CRIT "Unable to register AARP with SNAP.\n");
                return -ENOMEM;
        }
        timer_setup(&aarp_timer, aarp_expire_timeout, 0);
        aarp_timer.expires  = jiffies + sysctl_aarp_expiry_time;
        add_timer(&aarp_timer);
        rc = register_netdevice_notifier(&aarp_notifier);
        if (rc) {
                del_timer_sync(&aarp_timer);
                unregister_snap_client(aarp_dl);
        }
        return rc;
}

/* Remove the AARP entries associated with a device. */
void aarp_device_down(struct net_device *dev)
{
        int ct;

        write_lock_bh(&aarp_lock);

        for (ct = 0; ct < AARP_HASH_SIZE; ct++) {
                __aarp_expire_device(&resolved[ct], dev);
                __aarp_expire_device(&unresolved[ct], dev);
                __aarp_expire_device(&proxies[ct], dev);
        }

        write_unlock_bh(&aarp_lock);
}

#ifdef CONFIG_PROC_FS
/*
 * Get the aarp entry that is in the chain described
 * by the iterator.
 * If pos is set then skip till that index.
 * pos = 1 is the first entry
 */
static struct aarp_entry *iter_next(struct aarp_iter_state *iter, loff_t *pos)
{
        int ct = iter->bucket;
        struct aarp_entry **table = iter->table;
        loff_t off = 0;
        struct aarp_entry *entry;

 rescan:
        while (ct < AARP_HASH_SIZE) {
                for (entry = table[ct]; entry; entry = entry->next) {
                        if (!pos || ++off == *pos) {
                                iter->table = table;
                                iter->bucket = ct;
                                return entry;
                        }
                }
                ++ct;
        }

        if (table == resolved) {
                ct = 0;
                table = unresolved;
                goto rescan;
        }
        if (table == unresolved) {
                ct = 0;
                table = proxies;
                goto rescan;
        }
        return NULL;
}

static void *aarp_seq_start(struct seq_file *seq, loff_t *pos)
        __acquires(aarp_lock)
{
        struct aarp_iter_state *iter = seq->private;

        read_lock_bh(&aarp_lock);
        iter->table     = resolved;
        iter->bucket    = 0;

        return *pos ? iter_next(iter, pos) : SEQ_START_TOKEN;
}

static void *aarp_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct aarp_entry *entry = v;
        struct aarp_iter_state *iter = seq->private;

        ++*pos;

        /* first line after header */
        if (v == SEQ_START_TOKEN)
                entry = iter_next(iter, NULL);

        /* next entry in current bucket */
        else if (entry->next)
                entry = entry->next;

        /* next bucket or table */
        else {
                ++iter->bucket;
                entry = iter_next(iter, NULL);
        }
        return entry;
}

static void aarp_seq_stop(struct seq_file *seq, void *v)
        __releases(aarp_lock)
{
        read_unlock_bh(&aarp_lock);
}

static const char *dt2str(unsigned long ticks)
{
        static char buf[32];

        sprintf(buf, "%ld.%02ld", ticks / HZ, ((ticks % HZ) * 100) / HZ);

        return buf;
}

static int aarp_seq_show(struct seq_file *seq, void *v)
{
        struct aarp_iter_state *iter = seq->private;
        struct aarp_entry *entry = v;
        unsigned long now = jiffies;

        if (v == SEQ_START_TOKEN)
                seq_puts(seq,
                         "Address  Interface   Hardware Address"
                         "   Expires LastSend  Retry Status\n");
        else {
                seq_printf(seq, "%04X:%02X  %-12s",
                           ntohs(entry->target_addr.s_net),
                           (unsigned int) entry->target_addr.s_node,
                           entry->dev ? entry->dev->name : "????");
                seq_printf(seq, "%pM", entry->hwaddr);
                seq_printf(seq, " %8s",
                           dt2str((long)entry->expires_at - (long)now));
                if (iter->table == unresolved)
                        seq_printf(seq, " %8s %6hu",
                                   dt2str(now - entry->last_sent),
                                   entry->xmit_count);
                else
                        seq_puts(seq, "                ");
                seq_printf(seq, " %s\n",
                           (iter->table == resolved) ? "resolved"
                           : (iter->table == unresolved) ? "unresolved"
                           : (iter->table == proxies) ? "proxies"
                           : "unknown");
        }
        return 0;
}

const struct seq_operations aarp_seq_ops = {
        .start  = aarp_seq_start,
        .next   = aarp_seq_next,
        .stop   = aarp_seq_stop,
        .show   = aarp_seq_show,
};
#endif

/* General module cleanup. Called from cleanup_module() in ddp.c. */
void aarp_cleanup_module(void)
{
        del_timer_sync(&aarp_timer);
        unregister_netdevice_notifier(&aarp_notifier);
        unregister_snap_client(aarp_dl);
        aarp_purge();
}