1 .\" $NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $
3 .\" Copyright (c) 1996 Matthew R. Green
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34 .Nm pfil_head_register ,
35 .Nm pfil_head_unregister ,
38 .Nm pfil_remove_hook ,
40 .Nd packet filter interface
47 .Fn (*pfil_func_t) "void *arg" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
49 .Fn pfil_head_register "struct pfil_head *ph"
51 .Fn pfil_head_unregister "struct pfil_head *pfh"
52 .Ft struct pfil_head *
53 .Fn pfil_head_get "int type" "u_long val"
55 .Fn pfil_add_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph"
57 .Fn pfil_remove_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph"
59 .Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
63 framework allows for a specified function to be invoked for every
64 incoming or outgoing packet for a particular network I/O stream.
65 These hooks may be used to implement a firewall or perform packet
68 Packet filtering points are registered with
69 .Fn pfil_head_register .
70 Filtering points are identified by a key (void *) and a data link type
74 Packet filters use the key and data link type to look up the filtering
75 point with which they register themselves.
76 The key is unique to the filtering point.
77 The data link type is a
79 DLT constant indicating what kind of header is present on the packet
80 at the filtering point.
81 Filtering points may be unregistered with the
82 .Fn pfil_head_unregister
85 Packet filters register/unregister themselves with a filtering point
90 functions, respectively.
91 The head is looked up using the
93 function, which takes the key and data link type that the packet filter
95 Filters may provide an argument to be passed to the filter when
98 When a filter is invoked, the packet appears just as if it
99 .Dq came off the wire .
100 That is, all protocol fields are in network byte order.
101 The filter is called with its specified argument, the pointer to the
102 pointer to the mbuf containing the packet, the pointer to the network
103 interface that the packet is traversing, and the direction
107 see also below) that the packet is traveling.
108 The filter may change which mbuf the mbuf ** argument references.
109 The filter returns an
111 if the packet processing is to stop, or 0 if the processing is to continue.
112 If the packet processing is to stop, it is the responsibility of the
113 filter to free the packet.
117 parameter, used in the
121 functions, indicates when the filter should be called.
123 .Bl -tag -offset indent -width ".Dv PFIL_MPSAFE" -compact
125 call me on incoming packets
127 call me on outgoing packets
129 call me on all of the above
138 interface first appeared in
142 input and output lists were originally implemented as
146 however this was changed in
151 This change was to allow the input and output filters to be processed in
152 reverse order, to allow the same path to be taken, in or out of the kernel.
156 interface was changed in 1.4T to accept a 3rd parameter to both
159 .Fn pfil_remove_hook ,
160 introducing the capability of per-protocol filtering.
161 This was done primarily in order to support filtering of IPv6.
165 framework was changed to work with an arbitrary number of filtering points,
166 as well as be less IP-centric.
170 interface was imported from
174 and was reworked to suit a threaded kernel model in
179 interface was designed and implemented by Matthew R. Green, with help
180 from Darren Reed, Jason R. Thorpe and Charles M. Hannum.
181 Darren Reed added support for IPv6 in addition to IPv4.
182 Jason R. Thorpe added support for multiple hooks and other clean up.