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1 perry 1 NETLINK
2 !!!NETLINK
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 ADDRESS FORMATS
7 BUGS
8 NOTES
9 VERSIONS
10 SEE ALSO
11 ----
12 !!NAME
13
14
15 netlink, PF_NETLINK - Communication between kernel and user.
16 !!SYNOPSIS
17
18
19 __#include
20 __ ''socket_type''__,__ ''netlink_family''__);
21 __
22 !!DESCRIPTION
23
24
25 Netlink is used to transfer information between kernel
26 modules and user space processes. It consists of a standard
27 sockets based interface for user processes and an internal
28 kernel API for kernel modules. The internal kernel interface
29 is not documented in this man page. Also there is an
30 obsolete netlink interface via netlink character devices,
31 this interface is not documented here and is only provided
32 for backwards compatibility.
33
34
35 Netlink is a datagram oriented service. Both __SOCK_RAW__
36 and __SOCK_DGRAM__ are valid values for
37 ''socket_type''; however the netlink protocol does not
38 distinguish between datagram and raw sockets.
39
40
41 ''netlink_family'' selects the kernel module or netlink
42 group to communicate with. The currently assigned netlink
43 families are:
44
45
46 __NETLINK_ROUTE__
47
48
49 Receives routing updates and may be used to modify the IPv4
50 routing table (see rtnetlink(7)).
51
52
53 __NETLINK_FIREWALL__
54
55
56 Receives packets sent by the IPv4 firewall
57 code.
58
59
60 __NETLINK_ARPD__
61
62
63 For managing the arp table in user space.
64
65
66 __NETLINK_ROUTE6__
67
68
69 Receives and sends IPv6 routing table updates.
70
71
72 __NETLINK_IP6_FW__
73
74
75 to receive packets that failed the IPv6 firewall checks
76 (currently not implemented).
77
78
79 __NETLINK_TAPBASE__...__NETLINK_TAPBASE+15__
80
81
82 are the instances of the __ethertap__ device. Ethertap is
83 a pseudo network tunnel device that allows an ethernet
84 driver to be simulated from user space.
85
86
87 __NETLINK_SKIP__
88
89
90 Reserved for ENskip.
91
92
93 __NETLINK_USERSOCK__
94
95
96 is reserved for future user space protocols.
97
98
99 Netlink messages consist of a byte stream with one or
100 multiple __nlmsghdr__ headers and associated payload. For
101 multipart messages the first and all following headers have
102 the __NLM_F_MULTI__ flag set, except for the last header
103 which has the type __NLMSG_DONE__. The byte stream should
104 only be accessed with the standard __NLMSG_*__ macros,
105 see netlink(3).
106
107
108 Netlink is not a reliable protocol. It tries its best to
109 deliver a message to its destination(s), but may drop
110 messages when an out of memory condition or other error
111 occurs. For reliable transfer the sender can request an
112 acknowledgement from the receiver by setting the
113 __NLM_F_ACK__ flag. An acknowledgment is an
114 __NLMSG_ERROR__ packet with the error field set to 0. The
115 application must generate acks for received messages itself.
116 The kernel tries to send an __NLMSG_ERROR__ message for
117 every failed packet. A user process should follow this
118 convention too.
119
120
121 Each netlink family has a set of 32 multicast groups. When
122 bind(2) is called on the socket, the __nl_groups__
123 field in the __sockaddr_nl__ should be set to a bitmask
124 of the groups which it wishes to listen to. The default
125 value for this field is zero which means that no multicasts
126 will be received. A socket may multicast messages to any of
127 the multicast groups by setting __nl_groups__ to a
128 bitmask of the groups it wishes to send to when it calls
129 sendmsg(2) or does a connect(2). Only users
130 with an effective uid of 0 or the __CAP_NET_ADMIN__
131 capability may send or listen to a netlink multicast group.
132 Any replies to a message received for a multicast group
133 should be sent back to the sending pid and the multicast
134 group.
135
136
137 struct nlmsghdr
138 {
139 __u32 nlmsg_len; /* Length of message including header */
140 __u16 nlmsg_type; /* Message content */
141 __u16 nlmsg_flags;/* Additional flags */
142 __u32 nlmsg_seq; /* Sequence number */
143 __u32 nlmsg_pid; /* PID of the process that opened the socket */
144 };
145 struct nlmsgerr
146 {
147 int error; /* negative errno or 0 for acks. */
148 struct nlmsghdr msg; /* message header that caused the error */
149 };
150
151
152 After each __nlmsghdr__ the payload follows.
153 __nlmsg_type__ can be one of the standard message types:
154 __NLMSG_NOOP__ message is to be ignored,
155 __NLMSG_ERROR__ the message signals an error and the
156 payload contains a ''nlmsgerr'' structure,
157 __NLMSG_DONE__ message terminates a multipart
158 message,
159
160
161 A netlink family usually specifies more message types, see
162 the appropriate man pages for that, e.g. rtnetlink(7)
163 for ''NETLINK_ROUTE''.
164
165
166 Note that NLM_F_ATOMIC requires CAP_NET_ADMIN or super user rights.
167 !!ADDRESS FORMATS
168
169
170 The __sockaddr_nl__ structure describes a netlink client
171 in user space or in the kernel. A sockaddr_nl can be either
172 unicast (only send to one peer) or send to netlink groups
173 (nl_groups not equal 0).
174
175
176 struct sockaddr_nl
177 {
178 sa_family_t nl_family; /* AF_NETLINK */
179 unsigned short nl_pad; /* zero */
180 pid_t nl_pid; /* process pid */
181 __u32 nl_groups; /* multicast groups mask */
182 };
183
184
185 __nl_pid__ is the pid of the process owning the
186 destination socket, or 0 if the destination is in the
187 kernel. __nl_groups__ is a bitmask with every bit
188 representing a netlink group number.
189 !!BUGS
190
191
192 This man page is not complete.
193 !!NOTES
194
195
196 It is often better to use netlink via __libnetlink__ than
197 via the low level kernel interface.
198 !!VERSIONS
199
200
201 The socket interface to netlink is a new feature of Linux
202 2.2
203
204
205 Linux 2.0 supported a more primitive device based netlink
206 interface (which is still available as a compatibility
207 option). This obsolete interface is not described
208 here.
209 !!SEE ALSO
210
211
212 cmsg(3), rtnetlink(7),
213 netlink(3)
214
215
216 ftp://ftp.inr.ac.ru/ip-routing/iproute2* for
217 libnetlink
218 ----
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