rtnetlink man page on Manjaro

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RTNETLINK(3)		   Linux Programmer's Manual		  RTNETLINK(3)

NAME
       rtnetlink - macros to manipulate rtnetlink messages

SYNOPSIS
       #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 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);

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 mes‐
       sage, 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.

CONFORMING TO
       These macros are nonstandard Linux extensions.

BUGS
       This manual page is incomplete.

EXAMPLE
       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(struct ifinfomsg));
	   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(unsigned int));
	   req.n.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);

SEE ALSO
       netlink(3), netlink(7), rtnetlink(7)

COLOPHON
       This page is part of release 3.65 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2012-03-24			  RTNETLINK(3)
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