RTNETLINK(K)        Linux Programmer's Manual        RTNETLINK(K)



NAME
       rtnetlink - Macros to manipuate rtnetlink messages

SYNOPSIS
       #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);

DESCRIPTION
       All  rtnetlink(k) messages consist of a netlink(k) 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(A)  returns  a  pointer  to  the  start of this
       attribute's data.
       RTA_PAYLOAD(D) 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(H) returns the length which is  required  for
       len bytes of data plus the header.
       RTA_SPACE(E)  returns  the amount of space which will be
       needed in the message with len bytes of data.


EXAMPLE
       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(f));
            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) +
                      NLMSG_ALIGN(n->nlmsg_len));
            rta->rta_type = IFLA_MTU;
            rta->rta_len = sizeof(unsigned int);
            req.n.nlmsg_len = NLMSG_ALIGN(req.n.nlmsg_len) +
                      RTA_LENGTH(sizeof(f));
            memcpy(RTA_DATA(A), &mtu, sizeof (mtu));
            send(rtnetlink_sk, &req, req.n.nlmsg_len);


BUGS
       This manual page is lacking and incomplete.


SEE ALSO
       rtnetlink(k), netlink(k), netlink(k)




Linux Man Page              1999-05-14               RTNETLINK(K)