aarp.c

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/*
 *  AARP:       An implementation of the AppleTalk AARP protocol for
 *          Ethernet 'ELAP'.
 *
 *      Alan Cox  <[email protected]>
 *
 *  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.
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 *
 *  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>

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 {
    /* 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[6];
    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);

    memcpy(eah->hw_src, dev->dev_addr, ETH_ALEN);

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

    memset(eah->hw_dst, '\0', ETH_ALEN);

    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);

    memcpy(eah->hw_src, dev->dev_addr, ETH_ALEN);

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

    if (!sha)
        memset(eah->hw_dst, '\0', ETH_ALEN);
    else
        memcpy(eah->hw_dst, sha, ETH_ALEN);

    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);

    memcpy(eah->hw_src, dev->dev_addr, ETH_ALEN);

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

    memset(eah->hw_dst, '\0', ETH_ALEN);

    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(unsigned long 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 = 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. */
        memcpy(a->hwaddr, ea->hw_src, ETH_ALEN);
        __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 };

void __init aarp_proto_init(void)
{
    aarp_dl = register_snap_client(aarp_snap_id, aarp_rcv);
    if (!aarp_dl)
        printk(KERN_CRIT "Unable to register AARP with SNAP.\n");
    setup_timer(&aarp_timer, aarp_expire_timeout, 0);
    aarp_timer.expires  = jiffies + sysctl_aarp_expiry_time;
    add_timer(&aarp_timer);
    register_netdevice_notifier(&aarp_notifier);
}

/* 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
struct aarp_iter_state {
    int bucket;
    struct aarp_entry **table;
};

/*
 * 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;
}

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

static int aarp_seq_open(struct inode *inode, struct file *file)
{
    return seq_open_private(file, &aarp_seq_ops,
            sizeof(struct aarp_iter_state));
}

const struct file_operations atalk_seq_arp_fops = {
    .owner      = THIS_MODULE,
    .open           = aarp_seq_open,
    .read           = seq_read,
    .llseek         = seq_lseek,
    .release    = seq_release_private,
};
#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();
}