RTNETLINK(3) Linux Programmer's Manual RTNETLINK(3)

NAME
       rtnetlink - macros to manipulate rtnetlink messages

SYNOPSIS
       #include 
       #include 
       #include 
       #include 

       rtnetlinksocket = socket(AFNETLINK, int sockettype, NETLINKROUTE);

       int RTAOK(struct rtattr *rta, int rtabuflen);

       void *RTADATA(struct rtattr *rta);

       unsigned int RTAPAYLOAD(struct rtattr *rta);

       struct rtattr *RTANEXT(struct rtattr *rta, unsigned int rtabuflen);

       unsigned int RTALENGTH(unsigned int length);

       unsigned int RTASPACE(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.

       RTAOK(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 nonzero.

       RTADATA(rta) returns a pointer to the start of this attribute's data.

       RTAPAYLOAD(rta) returns the length of this attribute's data.

       RTANEXT(rta, attrlen) gets the next attribute after rta.  Calling this
       macro will update attrlen.  You should use RTAOK to check the validity
       of the returned pointer.

       RTALENGTH(len) returns the length which is required for len  bytes  of
       data plus the header.

       RTASPACE(len)  returns  the  amount of space which will be needed in a
       message with len bytes of data.

CONFORMING TO
       These macros are nonstandard Linux extensions.

BUGS
       This manual page is incomplete.

EXAMPLE
       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 rtnetlinksk = socket(AFNETLINK, SOCKDGRAM, NETLINKROUTE);

           memset(&req, 0, sizeof(req));
           req.nh.nlmsglen = NLMSGLENGTH(sizeof(struct ifinfomsg));
           req.nh.nlmsgflags = NLMFREQUEST;
           req.nh.nlmsgtype = RTMNEWLINK;
           req.if.ififamily = AFUNSPEC;
           req.if.ifiindex = INTERFACEINDEX;
           req.if.ifichange = 0xffffffff; /* ??? */
           rta = (struct rtattr *)(((char *) &req) +
                                    NLMSGALIGN(req.nh.nlmsglen));
           rta->rtatype = IFLAMTU;
           rta->rtalen = RTALENGTH(sizeof(unsigned int));
           req.n.nlmsglen = NLMSGALIGN(req.nh.nlmsglen) +
                                         RTALENGTH(sizeof(mtu));
           memcpy(RTADATA(rta), &mtu, sizeof(mtu));
           send(rtnetlinksk, &req, req.nh.nlmsglen);

SEE ALSO
       netlink(3), netlink(7), rtnetlink(7)

COLOPHON
       This page is part of release 3.53 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                               2012-03-24                      RTNETLINK(3)