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);
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.
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);