veth pair

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veth pari是用于不同nerwork namespace间进行通信的方式。其代码在driver/net/veth.c中
其入口函数如下：可以看出这是以模块的形参存在中的
static __init int veth_init(void)
{
	return rtnl_link_register(&veth_link_ops);
}

module_init(veth_init);
module_exit(veth_exit);

MODULE_DESCRIPTION("Virtual Ethernet Tunnel");

从veth_link_ops 的veth_newlink	 中可以看到veth 是将两个device绑定在一起

static struct rtnl_link_ops veth_link_ops = {
	.kind		= DRV_NAME,
	.priv_size	= sizeof(struct veth_priv),
	.setup		= veth_setup,
	.validate	= veth_validate,
	.newlink	= veth_newlink,
	.dellink	= veth_dellink,
	.policy		= veth_policy,
	.maxtype	= VETH_INFO_MAX,
	.get_link_net	= veth_get_link_net,
};

static int veth_newlink(struct net *src_net, struct net_device *dev,
			struct nlattr *tb[], struct nlattr *data[],
			struct netlink_ext_ack *extack)
{
		/*
	 * tie the deviced together
	 */

	priv = netdev_priv(dev);
	rcu_assign_pointer(priv->peer, peer);

	priv = netdev_priv(peer);
	rcu_assign_pointer(priv->peer, dev);
	return 0;
}

再看一下最重要的发送函数
static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct veth_priv *priv = netdev_priv(dev);
	struct net_device *rcv;
	int length = skb->len;

	rcu_read_lock();
#得到要发送的net_device rcv
	rcv = rcu_dereference(priv->peer);
	if (unlikely(!rcv)) {
		kfree_skb(skb);
		goto drop;
	}
#通过dev_forward_skb将skb数据发送到rcv中
	if (likely(dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) {
#发送成功后更新统计信息
		struct pcpu_vstats *stats = this_cpu_ptr(dev->vstats);

		u64_stats_update_begin(&stats->syncp);
		stats->bytes += length;
		stats->packets++;
		u64_stats_update_end(&stats->syncp);
	} else {
drop:
		atomic64_inc(&priv->dropped);
	}
	rcu_read_unlock();
	return NETDEV_TX_OK;
}