邻居表项的delay_probe_time时长

本文主要是介绍邻居表项的delay_probe_time时长，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

delay_probe_time控制首次发送邻居请求报文的等待时长，对于arp协议，内核默认的delay_probe_time时长为5秒钟。

struct neigh_table arp_tbl = {.family     = AF_INET,.key_len    = 4,.protocol   = cpu_to_be16(ETH_P_IP),.hash       = arp_hash,.key_eq     = arp_key_eq,.constructor    = arp_constructor,.proxy_redo = parp_redo,.id     = "arp_cache",.parms      = {.tbl            = &arp_tbl,.reachable_time     = 30 * HZ,.data   = {...[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,

通过PROC文件delay_first_probe_time可查看和修改此时长，如下，修改为10秒钟。

$ cat /proc/sys/net/ipv4/neigh/eth0/delay_first_probe_time 
5
$ echo 10 > /proc/sys/net/ipv4/neigh/eth0/delay_first_probe_time  
$     
$ cat /proc/sys/net/ipv4/neigh/eth0/delay_first_probe_time       
10

内核中静态变量neigh_sysctl_table定义了gc_stale_time的PROC文件信息。

static struct neigh_sysctl_table {struct ctl_table_header *sysctl_header;struct ctl_table neigh_vars[NEIGH_VAR_MAX + 1];
} neigh_sysctl_template __read_mostly = {.neigh_vars = {...NEIGH_SYSCTL_JIFFIES_ENTRY(DELAY_PROBE_TIME, "delay_first_probe_time"),

netlink接口

除了以上的PROC文件外，还可使用ip ntable命令查看和修改设备的邻居表参数。

# ip ntable show dev eth0
inet arp_cache dev eth0refcnt 12 reachable 28884 base_reachable 30000 retrans 1000 gc_stale 60000 delay_probe 5000 queue 31 app_probes 0 ucast_probes 3 mcast_probes 3 anycast_delay 1000 proxy_delay 800 proxy_queue 64 locktime 1000 

与PROC文件不同，这里显示的delay_probe时间单位为毫秒。如下将设备eth0的邻居表参数delay_probe修改为10秒钟。

# ip ntable change name arp_cache dev eth0 delay_probe 10000

内核函数neigh_init负责以上ip ntable change命令的处理。

static int __init neigh_init(void)
{...rtnl_register(PF_UNSPEC, RTM_SETNEIGHTBL, neightbl_set, NULL, 0);

如下为neightbl_set的实现，函数nla_get_msecs读取IP命令行设置的delay_probe_time的毫秒值参数。

static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh, struct netlink_ext_ack *extack)
{struct neigh_table *tbl;struct nlattr *tb[NDTA_MAX+1];if (tb[NDTA_PARMS]) {struct neigh_parms *p;p = lookup_neigh_parms(tbl, net, ifindex);...for (i = 1; i <= NDTPA_MAX; i++) {if (tbp[i] == NULL) continue;switch (i) {...case NDTPA_DELAY_PROBE_TIME:NEIGH_VAR_SET(p, DELAY_PROBE_TIME, nla_get_msecs(tbp[i]));call_netevent_notifiers(NETEVENT_DELAY_PROBE_TIME_UPDATE, p);break;

对于arp协议，宏NEIGH_VAR_SET将修改全局变量arp_tbl的成员parms的data数组，具体为以NEIGH_VAR_DELAY_PROBE_TIME为所对应的成员的值。函数nla_get_msecs将命令行输入的毫秒值转换为内核使用的jiffies值。

#define NEIGH_VAR_SET(p, attr, val) neigh_var_set(p, NEIGH_VAR_ ## attr, val)static inline void neigh_var_set(struct neigh_parms *p, int index, int val)
{                set_bit(index, p->data_state);p->data[index] = val;
}

显示命令ip ntable show由内核中的函数neightbl_fill_parms填充值，对于delay_probe_time的值，由nla_put_msecs填充。

static int neightbl_fill_parms(struct sk_buff *skb, struct neigh_parms *parms)
{...if ((parms->dev &&...nla_put_msecs(skb, NDTPA_DELAY_PROBE_TIME,NEIGH_VAR(parms, DELAY_PROBE_TIME), NDTPA_PAD) ||

如下函数nla_put_msecs，其需要将内核使用delay_probe_time的jiffies表示的值转换为ip ntable show显示时的毫秒值，通过jiffies_to_msecs实现。

static inline int nla_put_msecs(struct sk_buff *skb, int attrtype,unsigned long njiffies, int padattr)
{u64 tmp = jiffies_to_msecs(njiffies);return nla_put_64bit(skb, attrtype, sizeof(u64), &tmp, padattr);
}

delay_probe_time处理

如下邻居表项超时处理函数neigh_timer_handler，如果表项状态为NUD_REACHABLE，但是已经超过reachable_time规定的时长没有确认了，分成以下两种情况处理：

1） 此表项还在被使用，最后一次的使用时间戳到当下时刻还没有超出DELAY_PROBE_TIME（默认5秒钟）定义的时长，将表项状态设置为NUD_DELAY。
2） 如果条件1）不满足，即表项上一次使用时间戳到当下时刻时长超过DELAY_PROBE_TIME定义，将表项状态设置为NUD_STALE。

static void neigh_timer_handler(struct timer_list *t)
{struct neighbour *neigh = from_timer(neigh, t, timer);...state = neigh->nud_state;now = jiffies;next = now + HZ;if (!(state & NUD_IN_TIMER))goto out;if (state & NUD_REACHABLE) {if (time_before_eq(now,neigh->confirmed + neigh->parms->reachable_time)) {neigh_dbg(2, "neigh %p is still alive\n", neigh);next = neigh->confirmed + neigh->parms->reachable_time;} else if (time_before_eq(now,neigh->used +NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME))) {neigh_dbg(2, "neigh %p is delayed\n", neigh);neigh->nud_state = NUD_DELAY;neigh->updated = jiffies;neigh_suspect(neigh);next = now + NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME);} else {neigh_dbg(2, "neigh %p is suspected\n", neigh);neigh->nud_state = NUD_STALE;neigh->updated = jiffies;neigh_suspect(neigh);notify = 1;}

如果此表项的初始状态已经为NUD_DELAY，但是在定时器超时（DELAY_PROBE_TIME）之前，邻居表项得到了确认，重新将表项状态设置为NUD_REACHABLE。否则，如果表项没有被确认，将其状态设置为NUD_PROBE，发送ARP请求报文，由函数neigh_probe实现。

    } else if (state & NUD_DELAY) {if (time_before_eq(now,neigh->confirmed +NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME))) {neigh_dbg(2, "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_dbg(2, "neigh %p is probed\n", neigh);neigh->nud_state = NUD_PROBE;neigh->updated = jiffies;atomic_set(&neigh->probes, 0);notify = 1;next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME);}} else {/* NUD_PROBE|NUD_INCOMPLETE */next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME);}

邻居表项定时处理函数的时长不小于1/2秒。

    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)) {neigh_probe(neigh);} else {

另外，在数据报文发送流程中，如果检测到相应邻居表项的状态为NUD_STALE，将其设置为NUD_DELAY，之后将定时器超时时间设置为DELAY_PROBE_TIME，到期之后发送probe报文，以便更新邻居表项。

int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
{int rc;bool immediate_probe = false;write_lock_bh(&neigh->lock);rc = 0;if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))goto out_unlock_bh;if (neigh->dead)goto out_dead;if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {...} else if (neigh->nud_state & NUD_STALE) {neigh_dbg(2, "neigh %p is delayed\n", neigh);neigh->nud_state = NUD_DELAY;neigh->updated = jiffies;neigh_add_timer(neigh, jiffies +NEIGH_VAR(neigh->parms, DELAY_PROBE_TIME));}

内核版本 5.0

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