NLM_F_EXCL
nlm_flags = NLM_F_EXCL | NLM_F_CREATE;
hdr->nlmsg_flags &= ~(NLM_F_EXCL | NLM_F_APPEND);
hdr->nlmsg_flags |= NLM_F_CREATE | NLM_F_EXCL;
op_flags |= (nlm_flags & NLM_F_EXCL) ? RTM_F_EXCL : 0;
.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE | NLM_F_EXCL,
hdr->nlmsg_flags |= (NLM_F_CREATE | NLM_F_EXCL | NLM_F_REQUEST | NLM_F_ACK);