RTNETLINK(3) Linux Programmer's Manual RTNETLINK(3)NAMErtnetlink - 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 mes‐
sage, 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);
SEE ALSOnetlink(3), netlink(7), rtnetlink(7)COLOPHON
This page is part of release 3.65 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)
