NAME
rtnetlink − Macros to manipuate 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 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
the next attribute after rta. Calling this macro will
update 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 the message with len bytes of
data.
EXAMPLE
Creating a rtnetlink message to set a 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); |
BUGS
This manual page is lacking and incomplete.