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NAME | SYNOPSIS | DESCRIPTION | CONFORMING TO | BUGS | EXAMPLE | SEE ALSO | COLOPHON |
RTNETLINK(3) Linux Programmer's Manual RTNETLINK(3)
rtnetlink - macros to manipulate rtnetlink messages
#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);
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.
These macros are nonstandard Linux extensions.
This manual page is incomplete.
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);
netlink(3), netlink(7), rtnetlink(7)
This page is part of release 4.12 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/.
GNU 2014-09-06 RTNETLINK(3)
Pages that refer to this page: libnetlink(3), rtnetlink(7), sock_diag(7)