1RTNETLINK(3) Linux Programmer's Manual RTNETLINK(3)
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6 rtnetlink - macros to manipulate rtnetlink messages
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9 #include <asm/types.h>
10 #include <linux/netlink.h>
11 #include <linux/rtnetlink.h>
12 #include <sys/socket.h>
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14 rtnetlink_socket = socket(AF_NETLINK, int socket_type, NETLINK_ROUTE);
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16 int RTA_OK(struct rtattr *rta, int rtabuflen);
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18 void *RTA_DATA(struct rtattr *rta);
19 unsigned int RTA_PAYLOAD(struct rtattr *rta);
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21 struct rtattr *RTA_NEXT(struct rtattr *rta, unsigned int rtabuflen);
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23 unsigned int RTA_LENGTH(unsigned int length);
24 unsigned int RTA_SPACE(unsigned int length);
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27 All rtnetlink(7) messages consist of a netlink(7) message header and
28 appended attributes. The attributes should be manipulated only using
29 the macros provided here.
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31 RTA_OK(rta, attrlen) returns true if rta points to a valid routing at‐
32 tribute; attrlen is the running length of the attribute buffer. When
33 not true then you must assume there are no more attributes in the mes‐
34 sage, even if attrlen is nonzero.
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36 RTA_DATA(rta) returns a pointer to the start of this attribute's data.
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38 RTA_PAYLOAD(rta) returns the length of this attribute's data.
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40 RTA_NEXT(rta, attrlen) gets the next attribute after rta. Calling this
41 macro will update attrlen. You should use RTA_OK to check the validity
42 of the returned pointer.
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44 RTA_LENGTH(len) returns the length which is required for len bytes of
45 data plus the header.
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47 RTA_SPACE(len) returns the amount of space which will be needed in a
48 message with len bytes of data.
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51 These macros are nonstandard Linux extensions.
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54 This manual page is incomplete.
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57 Creating a rtnetlink message to set the MTU of a device:
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59 #include <linux/rtnetlink.h>
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61 ...
62
63 struct {
64 struct nlmsghdr nh;
65 struct ifinfomsg if;
66 char attrbuf[512];
67 } req;
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69 struct rtattr *rta;
70 unsigned int mtu = 1000;
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72 int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
73
74 memset(&req, 0, sizeof(req));
75 req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(req.if));
76 req.nh.nlmsg_flags = NLM_F_REQUEST;
77 req.nh.nlmsg_type = RTM_NEWLINK;
78 req.if.ifi_family = AF_UNSPEC;
79 req.if.ifi_index = INTERFACE_INDEX;
80 req.if.ifi_change = 0xffffffff; /* ??? */
81 rta = (struct rtattr *)(((char *) &req) +
82 NLMSG_ALIGN(req.nh.nlmsg_len));
83 rta->rta_type = IFLA_MTU;
84 rta->rta_len = RTA_LENGTH(sizeof(mtu));
85 req.nh.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
86 RTA_LENGTH(sizeof(mtu));
87 memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
88 send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0);
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91 netlink(3), netlink(7), rtnetlink(7)
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94 This page is part of release 5.13 of the Linux man-pages project. A
95 description of the project, information about reporting bugs, and the
96 latest version of this page, can be found at
97 https://www.kernel.org/doc/man-pages/.
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101GNU 2021-03-22 RTNETLINK(3)