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33 .\" Author: Archie Cobbs <archie@FreeBSD.org>
36 .\" $Whistle: ng_bpf.8,v 1.2 1999/12/03 01:57:12 archie Exp $
43 .Nd Berkeley packet filter netgraph node type
50 node type allows Berkeley Packet Filter (see
52 filters to be applied to data travelling through a Netgraph network.
53 Each node allows an arbitrary number of connections to arbitrarily
55 With each hook is associated a
57 filter program which is applied to incoming data only, a destination hook
58 for matching packets, a destination hook for non-matching packets,
59 and various statistics counters.
63 program returns an unsigned integer, which is normally interpreted as
64 the length of the prefix of the packet to return.
65 In the context of this
66 node type, returning zero is considered a non-match, in which case the
67 entire packet is delivered out the non-match destination hook.
68 Returning a value greater than zero causes the packet to be truncated
69 to that length and delivered out the match destination hook.
70 Either or both destination hooks may be the empty string, or may
71 not exist, in which case the packet is dropped.
73 New hooks are initially configured to drop all packets.
74 A new filter program may be installed using the
75 .Dv NGM_BPF_SET_PROGRAM
78 This node type supports any number of hooks having arbitrary names.
80 This node type supports the generic control messages, plus the following:
82 .It Dv NGM_BPF_SET_PROGRAM
83 This command sets the filter program that will be applied to incoming
85 The following structure must be supplied as an argument:
86 .Bd -literal -offset 4n
87 struct ng_bpf_hookprog {
88 char thisHook[NG_HOOKSIZ]; /* name of hook */
89 char ifMatch[NG_HOOKSIZ]; /* match dest hook */
90 char ifNotMatch[NG_HOOKSIZ]; /* !match dest hook */
91 int32_t bpf_prog_len; /* #isns in program */
92 struct bpf_insn bpf_prog[0]; /* bpf program */
96 The hook to be updated is specified in
98 The BPF program is the sequence of instructions in the
103 Matching and non-matching incoming packets are delivered out the hooks named
108 The program must be a valid
113 .It Dv NGM_BPF_GET_PROGRAM
114 This command takes an
116 string argument, the hook name, and returns the
118 .Dv "struct ng_bpf_hookprog"
120 .It Dv NGM_BPF_GET_STATS
121 This command takes an
123 string argument, the hook name, and returns the
124 statistics associated with the hook as a
125 .Dv "struct ng_bpf_hookstat" .
126 .It Dv NGM_BPF_CLR_STATS
127 This command takes an
129 string argument, the hook name, and clears the
130 statistics associated with the hook.
131 .It Dv NGM_BPF_GETCLR_STATS
132 This command is identical to
133 .Dv NGM_BPF_GET_STATS ,
134 except that the statistics are also atomically cleared.
137 This node shuts down upon receipt of a
139 control message, or when all hooks have been disconnected.
141 It is possible to configure a node from the command line, using
143 to generate raw BPF instructions which are then fed into an
145 script to create the ASCII form of a
146 .Dv NGM_BPF_SET_PROGRAM
147 control message, as demonstrated here:
148 .Bd -literal -offset 4n
151 PATTERN="tcp dst port 80"
157 cat > /tmp/bpf.awk << xxENDxx
160 printf "bpf_prog_len=%d bpf_prog=[", \\$1;
163 printf " { code=%d jt=%d jf=%d k=%d }", \\$1, \\$2, \\$3, \\$4;
171 BPFPROG=`tcpdump -s 8192 -ddd ${PATTERN} | awk -f /tmp/bpf.awk`
173 ngctl msg ${NODEPATH} setprogram { thisHook=\\"${INHOOK}\\" \\
174 ifMatch=\\"${MATCHHOOK}\\" \\
175 ifNotMatch=\\"${NOTMATCHHOOK}\\" \\
179 When built as a loadable kernel module, this module includes the file
180 .Pa net/bpf_filter.c .
181 Although loading the module should fail if
183 already exists in the kernel, currently it does not, and the duplicate
184 copies of the file do not interfere.
185 However, this may change in the future.
189 node type was implemented in
196 .An Archie Cobbs Aq archie@FreeBSD.org