c - 绑定(bind)与 SO_BINDTODEVICE 套接字

Question

我在 linux (ubuntu 13.10) 上运行一个项目，它使用连接到设备的原始套接字。

这是我的代码:

/* builed socket */
if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) == -1) {
  perror("listener: socket");
  return -1;
}

/* Set interface to promiscuous mode */
strncpy(ifopts.ifr_name, ifName, IFNAMSIZ-1);
ioctl(sockfd, SIOCGIFFLAGS, &ifopts);
ifopts.ifr_flags |= IFF_PROMISC;
ioctl(sockfd, SIOCSIFFLAGS, &ifopts);

/* Allow the socket to be reused - incase connection is closed prematurely */
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &sockopt, sizeof sockopt) == -1) {
  perror("setsockopt");
  close(sockfd);
  return -2;
}

但是我的计算机上有 2 个 NIC 卡，我只想听其中一个。让我们说民族风。我发现两个选项 bind 和 SO_BINDTODEVICE 如下:

/* option 1. Bind to device */
if (setsockopt(sockfd, SOL_SOCKET, SO_BINDTODEVICE, ifName, IFNAMSIZ-1) == -1)  {
  perror("SO_BINDTODEVICE");
  close(sockfd);
  return -4;
}


/* option 2. Bind to device */
memset(&sock_address, 0, sizeof(sock_address));
sock_address.sll_family = PF_PACKET;
sock_address.sll_protocol = htons(ETH_P_ALL);
sock_address.sll_ifindex = if_nametoindex(ifName);
if (bind(sockfd, (struct sockaddr*) &sock_address, sizeof(sock_address)) < 0) {
  perror("bind failed\n");
  close(sockfd);
  return -4;
}

只有绑定(bind)有效。所以我的问题是两者之间有什么区别？

Answer 1

来自 Linux 手册页 man 7 socket对于套接字选项 SO_BINDTODEVICE:

Note that this works only for some socket types, particularly AF_INET sockets. It is not supported for packet sockets (use normal bind(2) there).