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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |STANDARDS |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
rtnetlink(3) Library Functions Manualrtnetlink(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, intsocket_type, NETLINK_ROUTE);int RTA_OK(struct rtattr *rta, intsize);void *RTA_DATA(struct rtattr *rta);unsigned int RTA_PAYLOAD(struct rtattr *rta);struct rtattr *RTA_NEXT(struct rtattr *rta, unsigned intsize);unsigned int RTA_LENGTH(unsigned intsize);unsigned int RTA_SPACE(unsigned intsize);
Allrtnetlink(7) messages consist of anetlink(7) message header and appended attributes. The attributes should be manipulated only using the macros provided here.RTA_OK(rta,size)returns true ifrta 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 ifsize 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 afterrta. Calling this macro will updatesize. You should useRTA_OKto check the validity of the returned pointer.RTA_LENGTH(size)returns the size which is required forsize bytes of data plus the header.RTA_SPACE(size)returns the amount of space which will be needed in a message withsize 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 theman-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 isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17rtnetlink(3)Pages that refer to this page:libnetlink(3), rtnetlink(7), sock_diag(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |