ipv4對應的arp表格如下：
struct neigh_table arp_tbl = {
.family = AF_INET,
.entry_size = sizeof(struct neighbour) + 4,
.key_len = 4,
.hash = arp_hash,
.constructor = arp_constructor,
.proxy_redo = parp_redo,
.id = "arp_cache",
.parms = {
.tbl = &arp_tbl,
.base_reachable_time = 30 * HZ,
.retrans_time = 1 * HZ,
.gc_staletime = 60 * HZ,
.reachable_time = 30 * HZ,
.delay_probe_time = 5 * HZ,
.queue_len = 3,
.ucast_probes = 3,
.mcast_probes = 3,
.anycast_delay = 1 * HZ,
.proxy_delay = (8 * HZ) / 10,
.proxy_qlen = 64,
.locktime = 1 * HZ,
},
.gc_interval = 30 * HZ,
.gc_thresh1 = 128,
.gc_thresh2 = 512,
.gc_thresh3 = 1024,
};
EXPORT_SYMBOL(arp_tbl);
在arp_init函數中，對其初始化，并把它加入到neigh_tables對應的連結清單裡
void __init arp_init(void)
{
neigh_table_init(&arp_tbl);
dev_add_pack(&arp_packet_type);
arp_proc_init();
#ifdef CONFIG_SYSCTL
neigh_sysctl_register(NULL, &arp_tbl.parms, "ipv4", NULL);
#endif
register_netdevice_notifier(&arp_netdev_notifier);
}
void neigh_table_init(struct neigh_table *tbl)
{
struct neigh_table *tmp;
neigh_table_init_no_netlink(tbl);
write_lock(&neigh_tbl_lock);
for (tmp = neigh_tables; tmp; tmp = tmp->next) {
if (tmp->family == tbl->family)
break;
}
tbl->next = neigh_tables;
neigh_tables = tbl;
write_unlock(&neigh_tbl_lock);
if (unlikely(tmp)) {
printk(KERN_ERR "NEIGH: Registering multiple tables for "
"family %d\n", tbl->family);
dump_stack();
}
}
初始化中主要設計slab的建立，hash表的建立：
void neigh_table_init_no_netlink(struct neigh_table *tbl)
{
unsigned long now = jiffies;
unsigned long phsize;
write_pnet(&tbl->parms.net, &init_net);
atomic_set(&tbl->parms.refcnt, 1);
tbl->parms.reachable_time =
neigh_rand_reach_time(tbl->parms.base_reachable_time);
if (!tbl->kmem_cachep)
tbl->kmem_cachep =
kmem_cache_create(tbl->id, tbl->entry_size, 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC,
NULL);
tbl->stats = alloc_percpu(struct neigh_statistics);
if (!proc_create_data(tbl->id, 0, init_net.proc_net_stat,
&neigh_stat_seq_fops, tbl))
panic("cannot create neighbour proc dir entry");
RCU_INIT_POINTER(tbl->nht, neigh_hash_alloc(3));
phsize = (PNEIGH_HASHMASK + 1) * sizeof(struct pneigh_entry *);
tbl->phash_buckets = kzalloc(phsize, GFP_KERNEL);
rwlock_init(&tbl->lock);
INIT_DELAYED_WORK_DEFERRABLE(&tbl->gc_work, neigh_periodic_work);
schedule_delayed_work(&tbl->gc_work, tbl->parms.reachable_time);
setup_timer(&tbl->proxy_timer, neigh_proxy_process, (unsigned long)tbl);
skb_queue_head_init_class(&tbl->proxy_queue,
&neigh_table_proxy_queue_class);
tbl->last_flush = now;
tbl->last_rand = now + tbl->parms.reachable_time * 20;
}
在函數neigh_create中會建立新的neighbour資料結構：
struct neighbour *neigh_create(struct neigh_table *tbl,const void *pkey,
struct net_device *dev)
該函數首先配置設定記憶體，然後初始化：
u32 hash_val;
int key_len = tbl->key_len;
int error;
struct neighbour *n1, *rc, *n = neigh_alloc(tbl);
struct neigh_hash_table *nht;
memcpy(n->primary_key, pkey, key_len);
n->dev = dev;
/* Protocol specific setup. */
if (tbl->constructor && (error = tbl->constructor(n)) < 0) {
rc = ERR_PTR(error);
goto out_neigh_release;
}
/* Device specific setup. */
if (n->parms->neigh_setup &&
(error = n->parms->neigh_setup(n)) < 0) {
rc = ERR_PTR(error);
goto out_neigh_release;
}
n->confirmed = jiffies - (n->parms->base_reachable_time << 1);
static struct neighbour *neigh_alloc(struct neigh_table *tbl)
{
struct neighbour *n = NULL;
unsigned long now = jiffies;
int entries;
n = kmem_cache_zalloc(tbl->kmem_cachep, GFP_ATOMIC);
skb_queue_head_init(&n->arp_queue);
rwlock_init(&n->lock);
seqlock_init(&n->ha_lock);
n->updated = n->used = now;
n->nud_state = NUD_NONE;
n->output = neigh_blackhole;
seqlock_init(&n->hh.hh_lock);
n->parms = neigh_parms_clone(&tbl->parms);
setup_timer(&n->timer, neigh_timer_handler, (unsigned long)n);
NEIGH_CACHE_STAT_INC(tbl, allocs);
n->tbl = tbl;
atomic_set(&n->refcnt, 1);
n->dead = 1;
return n;
}
其中constructor會調用arp_constructor(struct neighbour *neigh)函數：
根據ip位址得到其類型，
static int arp_constructor(struct neighbour *neigh)
{
__be32 addr = *(__be32 *)neigh->primary_key;
struct net_device *dev = neigh->dev;
struct in_device *in_dev;
struct neigh_parms *parms;
rcu_read_lock();
in_dev = __in_dev_get_rcu(dev);
if (in_dev == NULL) {
rcu_read_unlock();
return -EINVAL;
}
neigh->type = inet_addr_type(dev_net(dev), addr);
parms = in_dev->arp_parms;
__neigh_parms_put(neigh->parms);
neigh->parms = neigh_parms_clone(parms);
rcu_read_unlock();
if (!dev->header_ops) { //在函數ether_setup中初始化為eth_header_ops
neigh->nud_state = NUD_NOARP;
neigh->ops = &arp_direct_ops;
neigh->output = neigh_direct_output;
} else {
if (neigh->type == RTN_MULTICAST) {
neigh->nud_state = NUD_NOARP;
arp_mc_map(addr, neigh->ha, dev, 1);
} else if (dev->flags & (IFF_NOARP | IFF_LOOPBACK)) {
neigh->nud_state = NUD_NOARP;
memcpy(neigh->ha, dev->dev_addr, dev->addr_len);
} else if (neigh->type == RTN_BROADCAST ||
(dev->flags & IFF_POINTOPOINT)) {
neigh->nud_state = NUD_NOARP;
memcpy(neigh->ha, dev->broadcast, dev->addr_len);
}
if (dev->header_ops->cache) //eth_header_cache
neigh->ops = &arp_hh_ops;
else
neigh->ops = &arp_generic_ops;
if (neigh->nud_state & NUD_VALID)
neigh->output = neigh->ops->connected_output;
else
neigh->output = neigh->ops->output; \\neigh_resolve_output
}
return 0;
} static inline unsigned __inet_dev_addr_type(struct net *net,
const struct net_device *dev,
__be32 addr)
{
struct flowi4 fl4 = { .daddr = addr };
struct fib_result res;
unsigned ret = RTN_BROADCAST;
struct fib_table *local_table;
if (ipv4_is_zeronet(addr) || ipv4_is_lbcast(addr))
return RTN_BROADCAST;
if (ipv4_is_multicast(addr))
return RTN_MULTICAST;
#ifdef CONFIG_IP_MULTIPLE_TABLES
res.r = NULL;
#endif
local_table = fib_get_table(net, RT_TABLE_LOCAL);
if (local_table) {
ret = RTN_UNICAST;
rcu_read_lock();
if (!fib_table_lookup(local_table, &fl4, &res, FIB_LOOKUP_NOREF)) {
if (!dev || dev == res.fi->fib_dev)
ret = res.type;
}
rcu_read_unlock();
}
return ret;
}
根據ip位址以及網卡裝置查找hash表，查不到的話添加到hash表中
nht = rcu_dereference_protected(tbl->nht,
lockdep_is_held(&tbl->lock));
if (atomic_read(&tbl->entries) > (1 << nht->hash_shift))
nht = neigh_hash_grow(tbl, nht->hash_shift + 1);
hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
if (n->parms->dead) {
rc = ERR_PTR(-EINVAL);
goto out_tbl_unlock;
}
for (n1 = rcu_dereference_protected(nht->hash_buckets[hash_val],
lockdep_is_held(&tbl->lock));
n1 != NULL;
n1 = rcu_dereference_protected(n1->next,
lockdep_is_held(&tbl->lock))) {
if (dev == n1->dev && !memcmp(n1->primary_key, pkey, key_len)) {
neigh_hold(n1);
rc = n1;
goto out_tbl_unlock;
}
}
n->dead = 0;
neigh_hold(n);
rcu_assign_pointer(n->next,
rcu_dereference_protected(nht->hash_buckets[hash_val],
lockdep_is_held(&tbl->lock)));
rcu_assign_pointer(nht->hash_buckets[hash_val], n);
write_unlock_bh(&tbl->lock);
NEIGH_PRINTK2("neigh %p is created.\n", n);
rc = n;
out:
return rc;
模拟neighbour查找的函數__ipv4_neigh_lookup，dump系統的neighbour資訊：
struct neigh_table *tbl=&arp_tbl;
struct neigh_hash_table *nht;
struct neighbour *n;
u32 hash_val;
printk("entry=%d\n",atomic_read(&tbl->entries));
nht = rcu_dereference_bh(tbl->nht);
for(hash_val=0;hash_val< 1<<nht->hash_shift;hash_val++){
for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
n != NULL;
n = rcu_dereference_bh(n->next)) {
printk("hash_val=%d,",hash_val);
printk("dev=%s,key=%x,state=%x,type=%d\n",n->dev->name,*(u32 *)n->primary_key,n->nud_state,n->type);
}
}
輸出：
[14799.054977] hash_val=0,dev=wlan0,key=6f01a8c0,state=2,type=1
[14799.054982] hash_val=1,dev=eth0,key=6fd20880,state=4,type=1
[14799.054987] hash_val=2,dev=wlan0,key=101a8c0,state=4,type=1
[14799.054992] hash_val=3,dev=eth0,key=160000e0,state=40,type=5
[14799.054996] hash_val=3,dev=wlan0,key=fb0000e0,state=40,type=5
[14799.055001] hash_val=8,dev=eth0,key=6ed20880,state=20,type=1
[14799.055006] hash_val=9,dev=eth0,key=70d20880,state=20,type=1
[14799.055010] hash_val=9,dev=lo,key=0,state=40,type=3
[14799.055015] hash_val=12,dev=eth0,key=fb0000e0,state=40,type=5
[email protected]:/opt/module/net/udp# arp -n
Address HWtype HWaddress Flags Mask Iface
192.168.1.111 ether 80:56:f2:db:2f:7b C wlan0
128.8.210.111 ether 3c:97:0e:cd:a4:6d C eth0
192.168.1.1 ether 00:23:cd:5b:ea:d6 C wlan0
128.8.210.110 (incomplete) eth0
128.8.210.112 (incomplete) eth0
狀态定義
#define NUD_INCOMPLETE 0x01
#define NUD_REACHABLE 0x02
#define NUD_STALE 0x04
#define NUD_DELAY 0x08
#define NUD_PROBE 0x10
#define NUD_FAILED 0x20
/* Dummy states */
#define NUD_NOARP 0x40
#define NUD_PERMANENT 0x80
#define NUD_NONE 0x00
enum {
RTN_UNSPEC,
RTN_UNICAST, /* Gateway or direct route */
RTN_LOCAL, /* Accept locally */
RTN_BROADCAST, /* Accept locally as broadcast,
send as broadcast */
RTN_ANYCAST, /* Accept locally as broadcast,
but send as unicast */
RTN_MULTICAST, /* Multicast route */
RTN_BLACKHOLE, /* Drop */
RTN_UNREACHABLE, /* Destination is unreachable */
RTN_PROHIBIT, /* Administratively prohibited */
RTN_THROW, /* Not in this table */
RTN_NAT, /* Translate this address */
RTN_XRESOLVE, /* Use external resolver */
__RTN_MAX
};
從上面可以知道,對于一般的以太網網卡,dev->header_ops=eth_header_ops,
const struct header_ops eth_header_ops ____cacheline_aligned = {
.create = eth_header,
.parse = eth_header_parse,
.rebuild = eth_rebuild_header,
.cache = eth_header_cache,
.cache_update = eth_header_cache_update,
};
建立的neighbour的neigh->ops = &arp_hh_ops;neigh->output =neigh_resolve_output
neigh_resolve_output函數位于L3和驅動發包之間,處理L2頭相關的事情,
ip_finish_output2----->neigh_output------> n->output(n, skb);
如果目前對應的neighbour狀态不是reachable,則發送arp請求封包
int neigh_resolve_output(struct neighbour *neigh, struct sk_buff *skb)
{
struct dst_entry *dst = skb_dst(skb);
int rc = 0;
if (!dst)
goto discard;
__skb_pull(skb, skb_network_offset(skb));
if (!neigh_event_send(neigh, skb)) {
int err;
struct net_device *dev = neigh->dev;
unsigned int seq;
if (dev->header_ops->cache && !neigh->hh.hh_len)
neigh_hh_init(neigh, dst);
do {
seq = read_seqbegin(&neigh->ha_lock);
err = dev_hard_header(skb, dev, ntohs(skb->protocol),
neigh->ha, NULL, skb->len);
} while (read_seqretry(&neigh->ha_lock, seq));
if (err >= 0)
rc = dev_queue_xmit(skb);
else
goto out_kfree_skb;
}
out:
return rc;
discard:
NEIGH_PRINTK1("neigh_resolve_output: dst=%p neigh=%p\n",
dst, neigh);
out_kfree_skb:
rc = -EINVAL;
kfree_skb(skb);
goto out;
}
首先分析neigh_hh_init函數:
static void neigh_hh_init(struct neighbour *n, struct dst_entry *dst)
{
struct net_device *dev = dst->dev;
__be16 prot = dst->ops->protocol;
struct hh_cache *hh = &n->hh;
write_lock_bh(&n->lock);
/* Only one thread can come in here and initialize the
* hh_cache entry.
*/
if (!hh->hh_len)
dev->header_ops->cache(n, hh, prot);
write_unlock_bh(&n->lock);
}
dst->ops在配置設定rtable的時候指派為ipv4_dst_ops，是以protocal為ETH_P_IP
static struct rtable *rt_dst_alloc(struct net_device *dev,
bool nopolicy, bool noxfrm)
{
return dst_alloc(&ipv4_dst_ops, dev, 1, -1,
DST_HOST |
(nopolicy ? DST_NOPOLICY : 0) |
(noxfrm ? DST_NOXFRM : 0));
}
static struct dst_ops ipv4_dst_ops = {
.family = AF_INET,
.protocol = cpu_to_be16(ETH_P_IP),
.gc = rt_garbage_collect,
.check = ipv4_dst_check,
.default_advmss = ipv4_default_advmss,
.default_mtu = ipv4_default_mtu,
.cow_metrics = ipv4_cow_metrics,
.destroy = ipv4_dst_destroy,
.ifdown = ipv4_dst_ifdown,
.negative_advice = ipv4_negative_advice,
.link_failure = ipv4_link_failure,
.update_pmtu = ip_rt_update_pmtu,
.local_out = __ip_local_out,
.neigh_lookup = ipv4_neigh_lookup,
};
最後調用eth_header_cache，主要是構造一個L2的和ader，緩存到hh_cache資料結構中,提高性能
{
struct ethhdr *eth;
const struct net_device *dev = neigh->dev;
eth = (struct ethhdr *)
(((u8 *) hh->hh_data) + (HH_DATA_OFF(sizeof(*eth))));
if (type == htons(ETH_P_802_3))
return -1;
eth->h_proto = type;
memcpy(eth->h_source, dev->dev_addr, ETH_ALEN); \\6
memcpy(eth->h_dest, neigh->ha, ETH_ALEN);
hh->hh_len = ETH_HLEN;\\14
return 0;
}
dev_hard_header調用eth_header建立L2的header
int eth_header(struct sk_buff *skb, struct net_device *dev,
unsigned short type,
const void *daddr, const void *saddr, unsigned len)
{
struct ethhdr *eth = (struct ethhdr *)skb_push(skb, ETH_HLEN);
if (type != ETH_P_802_3 && type != ETH_P_802_2)
eth->h_proto = htons(type);
else
eth->h_proto = htons(len); //第一次操作
/*
* Set the source hardware address.
*/
if (!saddr)
saddr = dev->dev_addr;
memcpy(eth->h_source, saddr, ETH_ALEN);//第二次操作
if (daddr) {
memcpy(eth->h_dest, daddr, ETH_ALEN); //第三次操作
return ETH_HLEN;
}
/*
* Anyway, the loopback-device should never use this function...
*/
if (dev->flags & (IFF_LOOPBACK | IFF_NOARP)) {
memset(eth->h_dest, 0, ETH_ALEN);
return ETH_HLEN;
}
return -ETH_HLEN;
}
對比下面的代碼可以看到L2 header緩存機制的作用
{
unsigned seq;
int hh_len;
do {
int hh_alen;
seq = read_seqbegin(&hh->hh_lock);
hh_len = hh->hh_len;
hh_alen = HH_DATA_ALIGN(hh_len);
memcpy(skb->data - hh_alen, hh->hh_data, hh_alen); //隻需一次操作
} while (read_seqretry(&hh->hh_lock, seq));
skb_push(skb, hh_len);
return dev_queue_xmit(skb);
}
static inline int neigh_output(struct neighbour *n, struct sk_buff *skb)
{
struct hh_cache *hh = &n->hh;
if ((n->nud_state & NUD_CONNECTED) && hh->hh_len)
return neigh_hh_output(hh, skb);
else
return n->output(n, skb);
}
前面的這幾個函數顯然需要negibour資料結構中有正确的MAC值了，即neigh_event_send傳回0
{
unsigned long now = jiffies;
if (neigh->used != now)
neigh->used = now;
if (!(neigh->nud_state&(NUD_CONNECTED|NUD_DELAY|NUD_PROBE)))
return __neigh_event_send(neigh, skb);
return 0;
}
int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
{
int rc;
unsigned long now;
write_lock_bh(&neigh->lock);
rc = 0;
if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))
goto out_unlock_bh;
now = jiffies;
if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {
if (neigh->parms->mcast_probes + neigh->parms->app_probes) {
atomic_set(&neigh->probes, neigh->parms->ucast_probes);
neigh->nud_state = NUD_INCOMPLETE;
neigh->updated = jiffies;
neigh_add_timer(neigh, now + 1); \\neigh_timer_handler
} else {
neigh->nud_state = NUD_FAILED;
neigh->updated = jiffies;
write_unlock_bh(&neigh->lock);
kfree_skb(skb);
return 1;
}
} else if (neigh->nud_state & NUD_STALE) {
NEIGH_PRINTK2("neigh %p is delayed.\n", neigh);
neigh->nud_state = NUD_DELAY;
neigh->updated = jiffies;
neigh_add_timer(neigh,
jiffies + neigh->parms->delay_probe_time);
}
if (neigh->nud_state == NUD_INCOMPLETE) {
if (skb) {
if (skb_queue_len(&neigh->arp_queue) >=
neigh->parms->queue_len) {
struct sk_buff *buff;
buff = __skb_dequeue(&neigh->arp_queue);
kfree_skb(buff);
NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards);
}
skb_dst_force(skb);
__skb_queue_tail(&neigh->arp_queue, skb);
}
rc = 1;
}
out_unlock_bh:
write_unlock_bh(&neigh->lock);
return rc;
}
static void neigh_timer_handler(unsigned long arg)
{
unsigned long now, next;
struct neighbour *neigh = (struct neighbour *)arg;
unsigned state;
int notify = 0;
write_lock(&neigh->lock);
state = neigh->nud_state;
now = jiffies;
next = now + HZ;
if (!(state & NUD_IN_TIMER)) {
#ifndef CONFIG_SMP
printk(KERN_WARNING "neigh: timer & !nud_in_timer\n");
#endif
goto out;
}
if (state & NUD_REACHABLE) {
if (time_before_eq(now,
neigh->confirmed + neigh->parms->reachable_time)) {
NEIGH_PRINTK2("neigh %p is still alive.\n", neigh);
next = neigh->confirmed + neigh->parms->reachable_time;
} else if (time_before_eq(now,
neigh->used + neigh->parms->delay_probe_time)) {
NEIGH_PRINTK2("neigh %p is delayed.\n", neigh);
neigh->nud_state = NUD_DELAY;
neigh->updated = jiffies;
neigh_suspect(neigh);
next = now + neigh->parms->delay_probe_time;
} else {
NEIGH_PRINTK2("neigh %p is suspected.\n", neigh);
neigh->nud_state = NUD_STALE;
neigh->updated = jiffies;
neigh_suspect(neigh);
notify = 1;
}
} else if (state & NUD_DELAY) {
if (time_before_eq(now,
neigh->confirmed + neigh->parms->delay_probe_time)) {
NEIGH_PRINTK2("neigh %p is now reachable.\n", neigh);
neigh->nud_state = NUD_REACHABLE;
neigh->updated = jiffies;
neigh_connect(neigh);
notify = 1;
next = neigh->confirmed + neigh->parms->reachable_time;
} else {
NEIGH_PRINTK2("neigh %p is probed.\n", neigh);
neigh->nud_state = NUD_PROBE;
neigh->updated = jiffies;
atomic_set(&neigh->probes, 0);
next = now + neigh->parms->retrans_time;
}
} else {
/* NUD_PROBE|NUD_INCOMPLETE */
next = now + neigh->parms->retrans_time;
}
if ((neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) &&
atomic_read(&neigh->probes) >= neigh_max_probes(neigh)) {
neigh->nud_state = NUD_FAILED;
notify = 1;
neigh_invalidate(neigh);
}
if (neigh->nud_state & NUD_IN_TIMER) {
if (time_before(next, jiffies + HZ/2))
next = jiffies + HZ/2;
if (!mod_timer(&neigh->timer, next))
neigh_hold(neigh);
}
if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) {
struct sk_buff *skb = skb_peek(&neigh->arp_queue);
/* keep skb alive even if arp_queue overflows */
if (skb)
skb = skb_copy(skb, GFP_ATOMIC);
write_unlock(&neigh->lock);
neigh->ops->solicit(neigh, skb); \\發送arp請求
atomic_inc(&neigh->probes);
kfree_skb(skb);
} else {
out:
write_unlock(&neigh->lock);
}
if (notify)
neigh_update_notify(neigh);
neigh_release(neigh);
}
我們以一個剛建立的neighbour為例，初始化的時候狀态為NUD_NONE，是以在函數__neigh_event_send中會把它的狀态設成NUD_INCOMPLETE，同時觸發定時器，把skb放入arp_queue隊列中定時器處理函數neigh_timer_handler調用arp_solicit發送arp請求在arp接收處理函數中會通過neigh_update函數發送挂在arp_queue上的skb<Understading Linux Networking Internals>描述的neighbour狀态之間的轉變關系
neigh_alloc中把初始狀态統一設成NUD_NONE；
arp_constructor會根據ip位址的類型，net_device的類型對一些特殊的情況進行處理，設成NUD_NOARP
__neigh_event_send根據之前的狀态作進一步處理;
如果是NUD_CONNECTED | NUD_DELAY | NUD_PROBE，不處理
如果是NUD_NONE，則設成NUD_INCOMPLETE，啟動1個jiffies後的定時器，然後把skb放入arp_queue中
如果已經是NUD_INCOMPLETE，把skb放入arp_queue中
如果是NUD_STALE，則設成NUD_DELAY，并啟動delay_probe_time後的定時器
定時器函數neigh_timer_handler處理NUD_IN_TIMER狀态，即NUD_INCOMPLETE|NUD_REACHABLE|NUD_DELAY|NUD_PROBE
如果是NUD_INCOMPLETE或者NUD_PROBE，如果probe次數還沒到最大值，啟動一個HZ/2後的定時器，發送arp請求
如果超過最到值，則設成NUD_FAILED
if ((neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) &&
atomic_read(&neigh->probes) >= neigh_max_probes(neigh)) {
neigh->nud_state = NUD_FAILED;
notify = 1;
neigh_invalidate(neigh);
} if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) {
struct sk_buff *skb = skb_peek(&neigh->arp_queue);
/* keep skb alive even if arp_queue overflows */
if (skb)
skb = skb_copy(skb, GFP_ATOMIC);
write_unlock(&neigh->lock);
neigh->ops->solicit(neigh, skb);
atomic_inc(&neigh->probes);
kfree_skb(skb);
}
如果是NUD_REACHABLE，根據使用情況，不改變狀态，啟動定時器；設成NUD_DELAY，啟動定時器；設成NUD_STALE
if (state & NUD_REACHABLE) {
if (time_before_eq(now,
neigh->confirmed + neigh->parms->reachable_time)) {
NEIGH_PRINTK2("neigh %p is still alive.\n", neigh);
next = neigh->confirmed + neigh->parms->reachable_time;
} else if (time_before_eq(now,
neigh->used + neigh->parms->delay_probe_time)) {
NEIGH_PRINTK2("neigh %p is delayed.\n", neigh);
neigh->nud_state = NUD_DELAY;
neigh->updated = jiffies;
neigh_suspect(neigh);
next = now + neigh->parms->delay_probe_time;
} else {
NEIGH_PRINTK2("neigh %p is suspected.\n", neigh);
neigh->nud_state = NUD_STALE;
neigh->updated = jiffies;
neigh_suspect(neigh);
notify = 1;
}
}
如果是NUD_DELAY，則根據情況設成NUD_REACHABLE或者NUD_PROBE
if (state & NUD_DELAY) {
if (time_before_eq(now,
neigh->confirmed + neigh->parms->delay_probe_time)) {
NEIGH_PRINTK2("neigh %p is now reachable.\n", neigh);
neigh->nud_state = NUD_REACHABLE;
neigh->updated = jiffies;
neigh_connect(neigh);
notify = 1;
next = neigh->confirmed + neigh->parms->reachable_time;
} else {
NEIGH_PRINTK2("neigh %p is probed.\n", neigh);
neigh->nud_state = NUD_PROBE;
neigh->updated = jiffies;
atomic_set(&neigh->probes, 0);
next = now + neigh->parms->retrans_time;
}
}
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