linux 内核 ：Netlink 原理分析_yzfcer的博客-CSDN博客

linux netlink实现机制：通信_老王不让用的博客-CSDN博客_linux netlink通信

Linux Netlink通信机制 用户空间与内核空间数据交互_liuzhanchun的博客-CSDN博客

笔记：

1、struct sock是struct socket在网络层所有协议的抽象表示，struct netlink_sock是struct sock的某一协议的具体表现。

 2、以pid为索引将所有套接字实例（都是指针形式）插入到哈希表中，再以pid为索引获取通信中的目标套接字实例。

3、套接字通信正常是用户进程间的通信，netlink是内核与用户进程的通信，把内核的pid固定为0，走的是特殊处理，这个处理就叫netlink协议。

4、nl_groups：如果用户空间的进程希望加入某个多播组，则必须执行bind()系统调用。该字段指明了调用者希望加入的多播组号的掩码(注意不是组号，后面我们会详细讲解这个字段)

     注：bind时是某个多播组，即一个多播组，如果设置了多个，只承认最低位表示的那个。

 5、32个组播组：

/* RTnetlink multicast groups */
enum rtnetlink_groups {
	RTNLGRP_NONE,
#define RTNLGRP_NONE		RTNLGRP_NONE
	RTNLGRP_LINK,
#define RTNLGRP_LINK		RTNLGRP_LINK
	RTNLGRP_NOTIFY,
#define RTNLGRP_NOTIFY		RTNLGRP_NOTIFY
	RTNLGRP_NEIGH,
#define RTNLGRP_NEIGH		RTNLGRP_NEIGH
	RTNLGRP_TC,
#define RTNLGRP_TC		RTNLGRP_TC
	RTNLGRP_IPV4_IFADDR,
#define RTNLGRP_IPV4_IFADDR	RTNLGRP_IPV4_IFADDR
	RTNLGRP_IPV4_MROUTE,
#define	RTNLGRP_IPV4_MROUTE	RTNLGRP_IPV4_MROUTE
	RTNLGRP_IPV4_ROUTE,
#define RTNLGRP_IPV4_ROUTE	RTNLGRP_IPV4_ROUTE
	RTNLGRP_IPV4_RULE,
#define RTNLGRP_IPV4_RULE	RTNLGRP_IPV4_RULE
	RTNLGRP_IPV6_IFADDR,
#define RTNLGRP_IPV6_IFADDR	RTNLGRP_IPV6_IFADDR
	RTNLGRP_IPV6_MROUTE,
#define RTNLGRP_IPV6_MROUTE	RTNLGRP_IPV6_MROUTE
	RTNLGRP_IPV6_ROUTE,
#define RTNLGRP_IPV6_ROUTE	RTNLGRP_IPV6_ROUTE
	RTNLGRP_IPV6_IFINFO,
#define RTNLGRP_IPV6_IFINFO	RTNLGRP_IPV6_IFINFO
	RTNLGRP_DECnet_IFADDR,
#define RTNLGRP_DECnet_IFADDR	RTNLGRP_DECnet_IFADDR
	RTNLGRP_NOP2,
	RTNLGRP_DECnet_ROUTE,
#define RTNLGRP_DECnet_ROUTE	RTNLGRP_DECnet_ROUTE
	RTNLGRP_DECnet_RULE,
#define RTNLGRP_DECnet_RULE	RTNLGRP_DECnet_RULE
	RTNLGRP_NOP4,
	RTNLGRP_IPV6_PREFIX,
#define RTNLGRP_IPV6_PREFIX	RTNLGRP_IPV6_PREFIX
	RTNLGRP_IPV6_RULE,
#define RTNLGRP_IPV6_RULE	RTNLGRP_IPV6_RULE
	RTNLGRP_ND_USEROPT,
#define RTNLGRP_ND_USEROPT	RTNLGRP_ND_USEROPT
	RTNLGRP_PHONET_IFADDR,
#define RTNLGRP_PHONET_IFADDR	RTNLGRP_PHONET_IFADDR
	RTNLGRP_PHONET_ROUTE,
#define RTNLGRP_PHONET_ROUTE	RTNLGRP_PHONET_ROUTE
	RTNLGRP_DCB,
#define RTNLGRP_DCB		RTNLGRP_DCB
	RTNLGRP_IPV4_NETCONF,
#define RTNLGRP_IPV4_NETCONF	RTNLGRP_IPV4_NETCONF
	RTNLGRP_IPV6_NETCONF,
#define RTNLGRP_IPV6_NETCONF	RTNLGRP_IPV6_NETCONF
	RTNLGRP_MDB,
#define RTNLGRP_MDB		RTNLGRP_MDB
	RTNLGRP_MPLS_ROUTE,
#define RTNLGRP_MPLS_ROUTE	RTNLGRP_MPLS_ROUTE
	RTNLGRP_NSID,
#define RTNLGRP_NSID		RTNLGRP_NSID
	RTNLGRP_MPLS_NETCONF,
#define RTNLGRP_MPLS_NETCONF	RTNLGRP_MPLS_NETCONF
	RTNLGRP_IPV4_MROUTE_R,
#define RTNLGRP_IPV4_MROUTE_R	RTNLGRP_IPV4_MROUTE_R
	RTNLGRP_IPV6_MROUTE_R,
#define RTNLGRP_IPV6_MROUTE_R	RTNLGRP_IPV6_MROUTE_R
	__RTNLGRP_MAX
};
#define RTNLGRP_MAX	(__RTNLGRP_MAX - 1)