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( |
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); |
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
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.
Creating a rtnetlink message to set the 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);