man3/rtnetlink.3

   1 .\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
   2 .\"
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   9 .\" $Id: rtnetlink.3,v 1.2 1999/05/18 10:35:10 freitag Exp $
  10 .TH RTNETLINK 3 2012-03-24 "GNU" "Linux Programmer's Manual"
  11 .SH NAME
  12 rtnetlink \- macros to manipulate rtnetlink messages
  13 .SH SYNOPSIS
  14 .B #include <asm/types.h>
  15 .br
  16 .B #include <linux/netlink.h>
  17 .br
  18 .B #include <linux/rtnetlink.h>
  19 .br
  20 .B #include <sys/socket.h>
  21
  22 .BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type \
  23 ", NETLINK_ROUTE);"
  24 .sp
  25 .BI "int RTA_OK(struct rtattr *" rta ", int " rtabuflen );
  26 .sp
  27 .BI "void *RTA_DATA(struct rtattr *" rta );
  28 .sp
  29 .BI "unsigned int RTA_PAYLOAD(struct rtattr *" rta );
  30 .sp
  31 .BI "struct rtattr *RTA_NEXT(struct rtattr *" rta \
  32 ", unsigned int " rtabuflen );
  33 .sp
  34 .BI "unsigned int RTA_LENGTH(unsigned int " length );
  35 .sp
  36 .BI "unsigned int RTA_SPACE(unsigned int "length );
  37 .SH DESCRIPTION
  38 All
  39 .BR rtnetlink (7)
  40 messages consist of a
  41 .BR netlink (7)
  42 message header and appended attributes.
  43 The attributes should be only
  44 manipulated using the macros provided here.
  45 .PP
  46 .BI RTA_OK( rta ", " attrlen )
  47 returns true if
  48 .I rta
  49 points to a valid routing attribute;
  50 .I attrlen
  51 is the running length of the attribute buffer.
  52 When not true then you must assume there are no more attributes in the
  53 message, even if
  54 .I attrlen
  55 is nonzero.
  56 .PP
  57 .BI RTA_DATA( rta )
  58 returns a pointer to the start of this attribute's data.
  59 .PP
  60 .BI RTA_PAYLOAD( rta )
  61 returns the length of this attribute's data.
  62 .PP
  63 .BI RTA_NEXT( rta ", " attrlen )
  64 gets the next attribute after
  65 .IR rta .
  66 Calling this macro will update
  67 .IR attrlen .
  68 You should use
  69 .B RTA_OK
  70 to check the validity of the returned pointer.
  71 .PP
  72 .BI RTA_LENGTH( len )
  73 returns the length which is required for
  74 .I len
  75 bytes of data plus the header.
  76 .PP
  77 .BI RTA_SPACE( len )
  78 returns the amount of space which will be needed in a message with
  79 .I len
  80 bytes of data.
  81 .SH CONFORMING TO
  82 These macros are nonstandard Linux extensions.
  83 .SH BUGS
  84 This manual page is incomplete.
  85 .SH EXAMPLE
  86 .\" FIXME ? would be better to use libnetlink in the EXAMPLE code here
  87
  88 Creating a rtnetlink message to set the MTU of a device:
  89 .nf
  90     #include <linux/rtnetlink.h>
  91
  92     ...
  93
  94     struct {
  95         struct nlmsghdr  nh;
  96         struct ifinfomsg if;
  97         char             attrbuf[512];
  98     } req;
  99
 100     struct rtattr *rta;
 101     unsigned int mtu = 1000;
 102
 103     int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
 104
 105     memset(&req, 0, sizeof(req));
 106     req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
 107     req.nh.nlmsg_flags = NLM_F_REQUEST;
 108     req.nh.nlmsg_type = RTM_NEWLINK;
 109     req.if.ifi_family = AF_UNSPEC;
 110     req.if.ifi_index = INTERFACE_INDEX;
 111     req.if.ifi_change = 0xffffffff; /* ??? */
 112     rta = (struct rtattr *)(((char *) &req) +
 113                              NLMSG_ALIGN(req.nh.nlmsg_len));
 114     rta\->rta_type = IFLA_MTU;
 115     rta\->rta_len = RTA_LENGTH(sizeof(unsigned int));
 116     req.n.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
 117                                   RTA_LENGTH(sizeof(mtu));
 118     memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
 119     send(rtnetlink_sk, &req, req.nh.nlmsg_len);
 120 .fi
 121 .SH SEE ALSO
 122 .BR netlink (3),
 123 .BR netlink (7),
 124 .BR rtnetlink (7)