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       rtnetlink - Macros to manipuate rtnetlink messages


       #include <asm/types.h>
       #include <linux/netlink.h>
       #include <linux/rtnetlink.h>
       #include <sys/socket.h>

       rtnetlink_socket = socket(PF_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);


       All  rtnetlink(7) messages consist of a netlink(7) message header and appended attributes.
       The attributes should be only manipulated 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 non-zero.
       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 for the validity of the returned pointer.
       RTA_LENGTH(len)  returns  the  length  which  is  required  for len bytes of data plus the
       RTA_SPACE(len) returns the amount of space which will be needed in the  message  with  len
       bytes of data.


       Creating a rtnetlink message to set a MTU of a device.
            struct {
                   struct nlmsghdr nh;
                   struct ifinfomsg   if;
                   char           attrbuf[512];
            } req;
            struct rtattr *rta;
            unsigned int mtu = 1000;
            int rtnetlink_sk = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);

            memset(&req, 0, sizeof(req));
            req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
            req.nh.nlmsg_flags = NLM_F_REQUEST;
            req.nh.nlmsg_type = RTML_NEWLINK;
            req.if.ifi_family = AF_UNSPEC;
            req.if.ifi_index = INTERFACE_INDEX;
            req.if.ifi_change = 0xffffffff; /* ???*/
            rta = (struct rtattr *)(((char *) &req) +
            rta->rta_type = IFLA_MTU;
            rta->rta_len = sizeof(unsigned int);
            req.n.nlmsg_len = NLMSG_ALIGN(req.n.nlmsg_len) +
            memcpy(RTA_DATA(rta), &mtu, sizeof (mtu));
            send(rtnetlink_sk, &req, req.n.nlmsg_len);


       This manual page is lacking and incomplete.


       rtnetlink(7), netlink(7), netlink(3)