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RTNETLINK(3)		   Linux Programmers Manual		 RTNETLINK(3)

       rtnetlink - macros to manipulate rtnetlink messages


       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 mes
       sage, even if attrlen is non-zero.

       RTA_DATA(rta) returns a pointer to the start of this attributes	data.

       RTA_PAYLOAD(rta) returns the length of this attributes 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.

       These macros are non-standard Linux extensions.

       This manual page is incomplete.

       Creating a rtnetlink message to set the 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);

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

       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  1999-05-14			  RTNETLINK(3)

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