RTNETLINK(3) Linux Programmer's Manual RTNETLINK(3)
NAME
rtnetlink(3,7) - Macros to manipuate rtnetlink(3,7) messages
SYNOPSIS
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <sys/socket.h>
rtnetlink_socket = socket(2,7,n)(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(3,7)(7) messages consist of a netlink(3,7)(7) message header and
appended attributes. The attributes should be only manipulated using
the macros provided here.
RTA_OK(rta, attrlen) returns true if(3,n) 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(1,8) the
message, even if(3,n) attrlen is non-zero.
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(3,n) the next attribute after rta. Calling this
macro will update(7,n) attrlen. You should use RTA_OK to check for 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(1,8) the
message with len bytes of data.
EXAMPLE
Creating a rtnetlink(3,7) message to set(7,n,1 builtins) a MTU of a device.
struct {
struct nlmsghdr nh;
struct ifinfomsg if(3,n);
char attrbuf[512];
} req;
struct rtattr *rta;
unsigned int mtu = 1000;
int rtnetlink_sk = socket(2,7,n)(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(2,n)(rtnetlink_sk, &req, req.n.nlmsg_len);
BUGS
This manual page is lacking and incomplete.
SEE ALSO
netlink(3,7)(3), netlink(3,7)(7), rtnetlink(3,7)(7)
Linux Man Page 1999-05-14 RTNETLINK(3)