网络函数bind源码分析

static int sock_bind(int fd, struct sockaddr *umyaddr, int addrlen)
{
	struct socket *sock;
	int i;
	char address[MAX_SOCK_ADDR];
	int err;

	if (fd < 0 || fd >= NR_OPEN || current->files->fd[fd] == NULL)
		return(-EBADF);
	// 通过文件描述符找到对应的socket，见socket函数源码分析的视图
	if (!(sock = sockfd_lookup(fd, NULL))) 
		return(-ENOTSOCK);
  
	if((err=move_addr_to_kernel(umyaddr,addrlen,address))<0)
	  	return err;
  
	if ((i = sock->ops->bind(sock, (struct sockaddr *)address, addrlen)) < 0) 
	{
		return(i);
	}
	return(0);
}
```
可见bind函数是直接调用底层af_inet.c的inet_bind
```c
// 给socket绑定一个地址
static int inet_bind(struct socket *sock, struct sockaddr *uaddr,
	       int addr_len)
{
	struct sockaddr_in *addr=(struct sockaddr_in *)uaddr;
	struct sock *sk=(struct sock *)sock->data, *sk2;
	unsigned short snum = 0 /* Stoopid compiler.. this IS ok */;
	int chk_addr_ret;

	/* check this error. */
	if (sk->state != TCP_CLOSE)
		return(-EIO);
	if(addr_len<sizeof(struct sockaddr_in))
		return -EINVAL;
	// raw是链路层，不需要端口	
	if(sock->type != SOCK_RAW)
	{	// 已经绑定了端口
		if (sk->num != 0) 
			return(-EINVAL);
		
		snum = ntohs(addr->sin_port);

		/*
		 * We can't just leave the socket bound wherever it is, it might
		 * be bound to a privileged port. However, since there seems to
		 * be a bug here, we will leave it if the port is not privileged.
		 */
		// 端口无效则随机获取一个非root才能使用的端口
		if (snum == 0) 
		{
			snum = get_new_socknum(sk->prot, 0);
		}
		// 小于1024的端口需要超级用户权限
		if (snum < PROT_SOCK && !suser()) 
			return(-EACCES);
	}
	// 判断ip
	chk_addr_ret = ip_chk_addr(addr->sin_addr.s_addr);
	if (addr->sin_addr.s_addr != 0 && chk_addr_ret != IS_MYADDR && chk_addr_ret != IS_MULTICAST)
		return(-EADDRNOTAVAIL);	/* Source address MUST be ours! */
	  	
	if (chk_addr_ret || addr->sin_addr.s_addr == 0)
		sk->saddr = addr->sin_addr.s_addr;
	
	if(sock->type != SOCK_RAW)
	{
		/* Make sure we are allowed to bind here. */
		cli();
		for(sk2 = sk->prot->sock_array[snum & (SOCK_ARRAY_SIZE -1)];
					sk2 != NULL; sk2 = sk2->next) 
		{
		/* should be below! */
			if (sk2->num != snum) 
				continue;
			// 端口已经被使用，没有设置可重用标记，比如断开了解后在2msl内是否可以重用
			if (!sk->reuse)
			{
				sti();
				return(-EADDRINUSE);
			}
			
			if (sk2->num != snum) 
				continue;		/* more than one */
			if (sk2->saddr != sk->saddr) 
				continue;	/* socket per slot ! -FB */
			// 被监听的端口不能同时被使用
			if (!sk2->reuse || sk2->state==TCP_LISTEN) 
			{
				sti();
				return(-EADDRINUSE);
			}
		}
		sti();
		// 保证该sk不在sock_array队列里
		remove_sock(sk);
		// 挂载到sock_array里
		put_sock(snum, sk);
		// tcp头中的源端口
		sk->dummy_th.source = ntohs(sk->num);
		sk->daddr = 0;
		sk->dummy_th.dest = 0;
	}
	return(0);
}
由代码中可以看到，bind函数主要做的事情是判断一下端口和ip和可用性，然后把sock结构体挂载到协议对应的sock_array哈希列表中。