rtnetlink(3)

NAME

   rtnetlink - macros to manipulate rtnetlink messages

SYNOPSIS

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

   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.

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 <linux/rtnetlink.h>

       ...

       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(struct ifinfomsg));
       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(unsigned int));
       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)

COLOPHON

   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.

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