/*
 * Perform the socket system call. we locate the appropriate
 * family, then create a fresh socket.
 */

static int sock_socket(int family, int type, int protocol)
{
 int i, fd;
 struct socket *sock;
 struct proto_ops *ops;

 /* Locate the correct protocol family. */
 for (i = 0; i < NPROTO; ++i) //查找对应的协议族
 {
  if (pops[i] == NULL) continue;
  if (pops[i]->family == family)
   break;
 }

 if (i == NPROTO) //查找未果，返回错误
 {
    return -EINVAL;
 }

 ops = pops[i];//指针指向该协议族的原型操作函数集

/*
 * Check that this is a type that we know how to manipulate and
 * the protocol makes sense here. The family can still reject the
 * protocol later.
 */
 
 if ((type != SOCK_STREAM && type != SOCK_DGRAM &&
  type != SOCK_SEQPACKET && type != SOCK_RAW &&
  type != SOCK_PACKET) || protocol < 0)
   return(-EINVAL);

/*
 * Allocate the socket and allow the family to set things up. if
 * the protocol is 0, the family is instructed to select an appropriate
 * default.
 */

 if (!(sock = sock_alloc())) //获取一个socket，已经完成了socket部分初始化设置
 {
  printk("NET: sock_socket: no more sockets\n");
  return(-ENOSR); /* Was: EAGAIN, but we are out of
       system resources! */
 }

 sock->type = type;
 sock->ops = ops;
 if ((i = sock->ops->create(sock, protocol)) < 0) //调用INET层函数，inet_create()函数，创建inet层的socket，即sock结构
 {
  sock_release(sock);
  return(i);
 }

 if ((fd = get_fd(SOCK_INODE(sock))) < 0) //根据sock结构中的inode，分配文件描述符
 {
  sock_release(sock);
  return(-EINVAL);
 }

 return(fd);
}