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(   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(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 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 non-standard Linux extensions.

BUGS

This manual page is incomplete.

EXAMPLE

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) +
                                  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(mtu));
    memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
    send(rtnetlink_sk, &req, req.n.nlmsg_len);

SEE ALSO

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

COLOPHON

This page is part of release 2.79 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/.


  This man page is Copyright (C) 1999 Andi Kleen <akmuc.de>.
Permission is granted to distribute possibly modified copies
of this page provided the header is included verbatim,
and in case of nontrivial modification author and date
of the modification is added to the header.
$Id: rtnetlink.3,v 1.2 1999/05/18 10:35:10 freitag Exp $