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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | STANDARDS | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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rtnetlink(3) Library Functions Manual rtnetlink(3)
rtnetlink - macros to manipulate rtnetlink messages
Standard C library (libc, -lc)
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <sys/socket.h>
rtnetlink_socket = socket(AF_NETLINK, int socket_type, NETLINK_ROUTE);
int RTA_OK(struct rtattr *rta, int size);
void *RTA_DATA(struct rtattr *rta);
unsigned int RTA_PAYLOAD(struct rtattr *rta);
struct rtattr *RTA_NEXT(struct rtattr *rta, unsigned int size);
unsigned int RTA_LENGTH(unsigned int size);
unsigned int RTA_SPACE(unsigned int size);
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, size) returns true if rta points to a valid routing
attribute; size is the running size of the attribute buffer. When
not true then you must assume there are no more attributes in the
message, even if size is nonzero.
RTA_DATA(rta) returns a pointer to the start of this attribute's
data.
RTA_PAYLOAD(rta) returns the size of this attribute's data.
RTA_NEXT(rta, size) gets the next attribute after rta. Calling
this macro will update size. You should use RTA_OK to check the
validity of the returned pointer.
RTA_LENGTH(size) returns the size which is required for size bytes
of data plus the header.
RTA_SPACE(size) returns the amount of space which will be needed
in a message with size bytes of data.
Linux.
This manual page is incomplete.
Creating a rtnetlink message to set the MTU of a device:
#include <linux/rtnetlink.h>
...
struct {
struct nlmsghdr nh;
struct ifinfomsg if;
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 +
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) +
RTA_LENGTH(sizeof(mtu));
memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0);
netlink(3), netlink(7), rtnetlink(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 rtnetlink(3)
Pages that refer to this page: libnetlink(3), rtnetlink(7), sock_diag(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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