man3/rtnetlink.3

   1 .\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
   2 .\" Permission is granted to distribute possibly modified copies
   3 .\" of this page provided the header is included verbatim,
   4 .\" and in case of nontrivial modification author and date
   5 .\" of the modification is added to the header.
   6 .\" $Id: rtnetlink.3,v 1.2 1999/05/18 10:35:10 freitag Exp $
   7 .TH RTNETLINK 3 2010-01-11 "GNU" "Linux Programmer's Manual"
   8 .SH NAME
   9 rtnetlink \- macros to manipulate rtnetlink messages
  10 .SH SYNOPSIS
  11 .B #include <asm/types.h>
  12 .br
  13 .B #include <linux/netlink.h>
  14 .br
  15 .B #include <linux/rtnetlink.h>
  16 .br
  17 .B #include <sys/socket.h>
  18
  19 .BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type \
  20 ", NETLINK_ROUTE);"
  21 .sp
  22 .BI "int RTA_OK(struct rtattr *" rta ", int " rtabuflen );
  23 .sp
  24 .BI "void *RTA_DATA(struct rtattr *" rta );
  25 .sp
  26 .BI "unsigned int RTA_PAYLOAD(struct rtattr *" rta );
  27 .sp
  28 .BI "struct rtattr *RTA_NEXT(struct rtattr *" rta \
  29 ", unsigned int " rtabuflen );
  30 .sp
  31 .BI "unsigned int RTA_LENGTH(unsigned int " length );
  32 .sp
  33 .BI "unsigned int RTA_SPACE(unsigned int "length );
  34 .SH DESCRIPTION
  35 All
  36 .BR rtnetlink (7)
  37 messages consist of a
  38 .BR netlink (7)
  39 message header and appended attributes.
  40 The attributes should be only
  41 manipulated using the macros provided here.
  42 .PP
  43 .BI RTA_OK( rta ", " attrlen )
  44 returns true if
  45 .I rta
  46 points to a valid routing attribute;
  47 .I attrlen
  48 is the running length of the attribute buffer.
  49 When not true then you must assume there are no more attributes in the
  50 message, even if
  51 .I attrlen
  52 is non-zero.
  53 .PP
  54 .BI RTA_DATA( rta )
  55 returns a pointer to the start of this attribute's data.
  56 .PP
  57 .BI RTA_PAYLOAD( rta )
  58 returns the length of this attribute's data.
  59 .PP
  60 .BI RTA_NEXT( rta ", " attrlen )
  61 gets the next attribute after
  62 .IR rta .
  63 Calling this macro will update
  64 .IR attrlen .
  65 You should use
  66 .B RTA_OK
  67 to check the validity of the returned pointer.
  68 .PP
  69 .BI RTA_LENGTH( len )
  70 returns the length which is required for
  71 .I len
  72 bytes of data plus the header.
  73 .PP
  74 .BI RTA_SPACE( len )
  75 returns the amount of space which will be needed in a message with
  76 .I len
  77 bytes of data.
  78 .SH CONFORMING TO
  79 These macros are nonstandard Linux extensions.
  80 .SH BUGS
  81 This manual page is incomplete.
  82 .SH EXAMPLE
  83 .\" FIXME ? would be better to use libnetlink in the EXAMPLE code here
  84
  85 Creating a rtnetlink message to set the MTU of a device:
  86 .nf
  87     #include <linux/rtnetlink.h>
  88
  89     ...
  90
  91     struct {
  92         struct nlmsghdr  nh;
  93         struct ifinfomsg if;
  94         char             attrbuf[512];
  95     } req;
  96
  97     struct rtattr *rta;
  98     unsigned int mtu = 1000;
  99
 100     int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
 101
 102     memset(&req, 0, sizeof(req));
 103     req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
 104     req.nh.nlmsg_flags = NLM_F_REQUEST;
 105     req.nh.nlmsg_type = RTM_NEWLINK;
 106     req.if.ifi_family = AF_UNSPEC;
 107     req.if.ifi_index = INTERFACE_INDEX;
 108     req.if.ifi_change = 0xffffffff; /* ???*/
 109     rta = (struct rtattr *)(((char *) &req) +
 110                                   NLMSG_ALIGN(req.nh.nlmsg_len));
 111     rta\->rta_type = IFLA_MTU;
 112     rta\->rta_len = sizeof(unsigned int);
 113     req.n.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
 114                                   RTA_LENGTH(sizeof(mtu));
 115     memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
 116     send(rtnetlink_sk, &req, req.nh.nlmsg_len);
 117 .fi
 118 .SH "SEE ALSO"
 119 .BR netlink (3),
 120 .BR netlink (7),
 121 .BR rtnetlink (7)