Linux C sockets - recvmsg - getting source ifindex

Question

I'm opening a RAW socket in Linux and reading all messages.

recvmsg(mysock, &msg, 0);

I'm traversing on all cmsg on that msg buffer and I get only one.

    for (c = CMSG_FIRSTHDR(&msg); c; c = CMSG_NXTHDR(&msg, c)) {

How can I extract the ifindex on which it received on ?

Answer 1

Found it. I had to set the IP_PKTINFO flag first:

setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &hold, sizeof(hold));