/* connect socket to NIC by name */
strcpy(ifr.ifr_name, ifname);
r = ioctl(*psock, SIOCGIFINDEX, &ifr);
ifindex = ifr.ifr_ifindex;
调试看到r的值为-1
（ifindex 却也能获得内容）
r = setsockopt(*psock, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
r = setsockopt(*psock, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof(timeout));
i = 1;
r = setsockopt(*psock, SOL_SOCKET, SO_DONTROUTE, &i, sizeof(i));
/* connect socket to NIC by name */
strcpy(ifr.ifr_name, ifname);
-》 r = ioctl(*psock, SIOCGIFINDEX, &ifr);
ifindex = ifr.ifr_ifindex;
strcpy(ifr.ifr_name, ifname);
ifr.ifr_flags = 0;
/* reset flags of NIC interface */
r = ioctl(*psock, SIOCGIFFLAGS, &ifr);
/* set flags of NIC interface, here promiscuous and broadcast */
ifr.ifr_flags = ifr.ifr_flags || IFF_PROMISC || IFF_BROADCAST;
r = ioctl(*psock, SIOCSIFFLAGS, &ifr);
/* bind socket to protocol, in this case RAW EtherCAT */
sll.sll_family = AF_PACKET;
sll.sll_ifindex = ifindex;
sll.sll_protocol = htons(ETH_P_ECAT);
r = bind(*psock, (struct sockaddr *)&sll, sizeof(sll));