NLM_F_ACK
if ((hdr->nlmsg_flags & NLM_F_ACK) || (error != 0 && error != EINTR)) {
hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
hdr->nlmsg_flags |= (NLM_F_CREATE | NLM_F_EXCL | NLM_F_REQUEST | NLM_F_ACK);
hdr->nlmsg_flags |= (NLM_F_ACK | NLM_F_REQUEST);