man3/rtnetlink.3

   1 .\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
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  10 .\" $Id: rtnetlink.3,v 1.2 1999/05/18 10:35:10 freitag Exp $
  11 .\"
  12 .TH RTNETLINK 3 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
  13 .SH NAME
  14 rtnetlink \- macros to manipulate rtnetlink messages
  15 .SH LIBRARY
  16 Standard C library
  17 .RI ( libc ", " \-lc )
  18 .SH SYNOPSIS
  19 .nf
  20 .B #include <asm/types.h>
  21 .B #include <linux/netlink.h>
  22 .B #include <linux/rtnetlink.h>
  23 .B #include <sys/socket.h>
  24 .PP
  25 .BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type \
  26 ", NETLINK_ROUTE);"
  27 .PP
  28 .BI "int RTA_OK(struct rtattr *" rta ", int " rtabuflen );
  29 .PP
  30 .BI "void *RTA_DATA(struct rtattr *" rta );
  31 .BI "unsigned int RTA_PAYLOAD(struct rtattr *" rta );
  32 .PP
  33 .BI "struct rtattr *RTA_NEXT(struct rtattr *" rta \
  34 ", unsigned int " rtabuflen );
  35 .PP
  36 .BI "unsigned int RTA_LENGTH(unsigned int " length );
  37 .BI "unsigned int RTA_SPACE(unsigned int "length );
  38 .fi
  39 .SH DESCRIPTION
  40 All
  41 .BR rtnetlink (7)
  42 messages consist of a
  43 .BR netlink (7)
  44 message header and appended attributes.
  45 The attributes should be manipulated only using the macros provided here.
  46 .PP
  47 .BI RTA_OK( rta ", " attrlen )
  48 returns true if
  49 .I rta
  50 points to a valid routing attribute;
  51 .I attrlen
  52 is the running length of the attribute buffer.
  53 When not true then you must assume there are no more attributes in the
  54 message, even if
  55 .I attrlen
  56 is nonzero.
  57 .PP
  58 .BI RTA_DATA( rta )
  59 returns a pointer to the start of this attribute's data.
  60 .PP
  61 .BI RTA_PAYLOAD( rta )
  62 returns the length of this attribute's data.
  63 .PP
  64 .BI RTA_NEXT( rta ", " attrlen )
  65 gets the next attribute after
  66 .IR rta .
  67 Calling this macro will update
  68 .IR attrlen .
  69 You should use
  70 .B RTA_OK
  71 to check the validity of the returned pointer.
  72 .PP
  73 .BI RTA_LENGTH( len )
  74 returns the length which is required for
  75 .I len
  76 bytes of data plus the header.
  77 .PP
  78 .BI RTA_SPACE( len )
  79 returns the amount of space which will be needed in a message with
  80 .I len
  81 bytes of data.
  82 .SH STANDARDS
  83 These macros are nonstandard Linux extensions.
  84 .SH BUGS
  85 This manual page is incomplete.
  86 .SH EXAMPLES
  87 .\" FIXME . ? would be better to use libnetlink in the EXAMPLE code here
  88 Creating a rtnetlink message to set the MTU of a device:
  89 .PP
  90 .in +4n
  91 .EX
  92 #include <linux/rtnetlink.h>
  93
  94 \&...
  95
  96 struct {
  97     struct nlmsghdr  nh;
  98     struct ifinfomsg if;
  99     char             attrbuf[512];
 100 } req;
 101
 102 struct rtattr *rta;
 103 unsigned int mtu = 1000;
 104
 105 int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
 106
 107 memset(&req, 0, sizeof(req));
 108 req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(req.if));
 109 req.nh.nlmsg_flags = NLM_F_REQUEST;
 110 req.nh.nlmsg_type = RTM_NEWLINK;
 111 req.if.ifi_family = AF_UNSPEC;
 112 req.if.ifi_index = INTERFACE_INDEX;
 113 req.if.ifi_change = 0xffffffff; /* ??? */
 114 rta = (struct rtattr *)(((char *) &req) +
 115                          NLMSG_ALIGN(req.nh.nlmsg_len));
 116 rta\->rta_type = IFLA_MTU;
 117 rta\->rta_len = RTA_LENGTH(sizeof(mtu));
 118 req.nh.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
 119                               RTA_LENGTH(sizeof(mtu));
 120 memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
 121 send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0);
 122 .EE
 123 .in
 124 .SH SEE ALSO
 125 .BR netlink (3),
 126 .BR netlink (7),
 127 .BR rtnetlink (7)