rtnetlink(3) — Linux manual pages

Linux manual pages	Section 3: Subroutines

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.n.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);

COLOPHON

This page is part of release 3.52 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>.

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$Id: rtnetlink.3,v 1.2 1999/05/18 10:35:10 freitag Exp $