//	inet协议族控制块
//		1.在inet_init中，由sock_register(&inet_family_ops)注册给系统
// 		2.在sys_socket系统调用中，通过协议族号查找对应的协议控制块，然后由
//		  具体协议控制块的create函数创建套接字
1.1 static const struct net_proto_family inet_family_ops = {
	.family = PF_INET,
	.create = inet_create,
	.owner	= THIS_MODULE,
};



//	创建inet协议族的socket套接字
//	步骤：
//		1.更具套接字类型，协议号，查找指定协议
//		2.初始化套接字操作集合(socket->ops)
//		3.分配sock结构，初始化sock->sk_prot指向inet_protosw->prot
//		4.初始化sock，建立struct sock与struct socket的连接
1.2 static int inet_create(struct net *net, struct socket *sock, int protocol,
		       int kern)
{
	struct sock *sk;
	struct inet_protosw *answer;
	struct inet_sock *inet;
	struct proto *answer_prot;

	int err;

	//未连接状态
	sock->state = SS_UNCONNECTED;

lookup_protocol:
	err = -ESOCKTNOSUPPORT;
	rcu_read_lock();
	//同一协议族下边具有相同套接字类型的多个不同协议
	list_for_each_entry_rcu(answer, &inetsw[sock->type], list) {

		err = 0;
		
		if (protocol == answer->protocol) {
			if (protocol != IPPROTO_IP)
				break;
		} else {
			//指定IPPROTO_IP表示匹配默认的套接字类型
			if (IPPROTO_IP == protocol) {
				protocol = answer->protocol;
				break;
			}
			//套接字类型的协议号为IPPROTO_IP，表示可以与任何协议匹配
			if (IPPROTO_IP == answer->protocol)
				break;
		}
		err = -EPROTONOSUPPORT;
	}

	//如果模块没有加载，加载协议模块
	...

	//初始化套接字操作，协议类型
	sock->ops = answer->ops; // (struct proto_ops)
	answer_prot = answer->prot; // (struct proto)
	answer_no_check = answer->no_check;
	answer_flags = answer->flags;
	rcu_read_unlock();


	err = -ENOBUFS;
	//分配sock结构
	sk = sk_alloc(net, PF_INET, GFP_KERNEL, answer_prot);
	if (sk == NULL)
		goto out;

	...

	//建立struct sock与struct socket的联系
	sock_init_data(sock, sk);

	...

out:
	return err;
out_rcu_unlock:
	rcu_read_unlock();
	goto out;
}


//	struct sock结构初始化
//		1.分配sock的队列
//		2.初始化sock各字段
//		3.设置sock->sk_socket字段指向socket
1.3 void sock_init_data(struct socket *sock, struct sock *sk)
{
	//分配sock的队列
	skb_queue_head_init(&sk->sk_receive_queue);
	skb_queue_head_init(&sk->sk_write_queue);
	skb_queue_head_init(&sk->sk_error_queue);
#ifdef CONFIG_NET_DMA
	skb_queue_head_init(&sk->sk_async_wait_queue);
#endif

	sk->sk_send_head	=	NULL;

	init_timer(&sk->sk_timer);

	sk->sk_allocation	=	GFP_KERNEL;
	//接收，发送缓存的大小
	sk->sk_rcvbuf		=	sysctl_rmem_default;
	sk->sk_sndbuf		=	sysctl_wmem_default;
	sk->sk_state		=	TCP_CLOSE;
	//sk->sk_socket = socket
	sk_set_socket(sk, sock);

	sock_set_flag(sk, SOCK_ZAPPED);

	if (sock) {
		sk->sk_type	=	sock->type;
		sk->sk_wq	=	sock->wq;
		sock->sk	=	sk;
	} else
		sk->sk_wq	=	NULL;

	sk->sk_state_change	=	sock_def_wakeup;
	sk->sk_data_ready	=	sock_def_readable;
	sk->sk_write_space	=	sock_def_write_space;
	sk->sk_error_report	=	sock_def_error_report;
	sk->sk_destruct		=	sock_def_destruct;

	sk->sk_frag.page	=	NULL;
	sk->sk_frag.offset	=	0;
	sk->sk_peek_off		=	-1;

	sk->sk_peer_pid 	=	NULL;
	sk->sk_peer_cred	=	NULL;
	sk->sk_write_pending	=	0;
	sk->sk_rcvlowat		=	1;
	sk->sk_rcvtimeo		=	MAX_SCHEDULE_TIMEOUT;
	sk->sk_sndtimeo		=	MAX_SCHEDULE_TIMEOUT;

	sk->sk_stamp = ktime_set(-1L, 0);

	smp_wmb();
	atomic_set(&sk->sk_refcnt, 1);
	atomic_set(&sk->sk_drops, 0);
}

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网络子系统78_inet套接字创建