rtnetlink(3) Library Functions Manual rtnetlink(3) NAME rtnetlink - macros to manipulate rtnetlink messages LIBRARY Standard C library (libc, -lc) SYNOPSIS #include #include #include #include rtnetlink_socket = socket(AF_NETLINK, int socket_type, NETLINK_ROUTE); int RTA_OK(struct rtattr *rta, int rtabuflen); void *RTA_DATA(struct rtattr *rta); unsigned int RTA_PAYLOAD(struct rtattr *rta); struct rtattr *RTA_NEXT(struct rtattr *rta, unsigned int rtabuflen); unsigned int RTA_LENGTH(unsigned int length); unsigned int RTA_SPACE(unsigned int length); DESCRIPTION All rtnetlink(7) messages consist of a netlink(7) message header and appended attributes. The attributes should be manipulated only using the macros provided here. RTA_OK(rta, attrlen) returns true if rta points to a valid routing attribute; attrlen is the running length of the attribute buffer. When not true then you must assume there are no more attributes in the message, even if attrlen is nonzero. RTA_DATA(rta) returns a pointer to the start of this attribute's data. RTA_PAYLOAD(rta) returns the length of this attribute's data. RTA_NEXT(rta, attrlen) gets the next attribute after rta. Calling this macro will update attrlen. You should use RTA_OK to check the validity of the returned pointer. RTA_LENGTH(len) returns the length which is required for len bytes of data plus the header. RTA_SPACE(len) returns the amount of space which will be needed in a message with len bytes of data. STANDARDS Linux. BUGS This manual page is incomplete. EXAMPLES Creating a rtnetlink message to set the MTU of a device: #include ... struct { struct nlmsghdr nh; struct ifinfomsg if; char attrbuf[512]; } req; struct rtattr *rta; unsigned int mtu = 1000; int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE); memset(&req, 0, sizeof(req)); req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(req.if)); req.nh.nlmsg_flags = NLM_F_REQUEST; req.nh.nlmsg_type = RTM_NEWLINK; req.if.ifi_family = AF_UNSPEC; req.if.ifi_index = INTERFACE_INDEX; req.if.ifi_change = 0xffffffff; /* ??? */ rta = (struct rtattr *)(((char *) &req) + NLMSG_ALIGN(req.nh.nlmsg_len)); rta->rta_type = IFLA_MTU; rta->rta_len = RTA_LENGTH(sizeof(mtu)); req.nh.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) + RTA_LENGTH(sizeof(mtu)); memcpy(RTA_DATA(rta), &mtu, sizeof(mtu)); send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0); SEE ALSO netlink(3), netlink(7), rtnetlink(7) Linux man-pages 6.9.1 2024-05-02 rtnetlink(3)