NAME
rtnetlink - macros to manipulate rtnetlink messages
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <asm/types.h>\n
\n#include <linux/netlink.h>\n
\n#include <linux/rtnetlink.h>\n
\n#include <sys/socket.h>rtnetlink_socket = socket(AF_NETLINK, int \nsocket_type\n, NETLINK_ROUTE);int RTA_OK(struct rtattr *\nrta\n, int \nrtabuflen\n);void *RTA_DATA(struct rtattr *\nrta\n);\n
\nunsigned int RTA_PAYLOAD(struct rtattr *\nrta\n);struct rtattr *RTA_NEXT(struct rtattr *\nrta\n, unsigned int \nrtabuflen\n);unsigned int RTA_LENGTH(unsigned int \nlength\n);\n
\nunsigned int RTA_SPACE(unsigned int \nlength\n);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 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.
STANDARDS
Linux.
BUGS
This manual page is incomplete.
EXAMPLES
Creating a rtnetlink message to set the MTU of a device:
#include <linux/rtnetlink.h>
...
struct {
\n
struct nlmsghdr nh;
\n
struct ifinfomsg if;
\n
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(req.if));
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) +
\n
NLMSG_ALIGN(req.nh.nlmsg_len));
rta->rta_type = IFLA_MTU;
rta->rta_len = RTA_LENGTH(sizeof(mtu));
req.nh.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
\n
RTA_LENGTH(sizeof(mtu));
memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0);SEE ALSO
netlink(3), netlink(7), rtnetlink(7)