1 .\" $NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $
2 .\" $DragonFly: src/share/man/man9/pfil.9,v 1.9 2008/09/20 06:08:13 sephe Exp $
4 .\" Copyright (c) 1996 Matthew R. Green
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30 .Dd September 15, 2008
35 .Nm pfil_head_register ,
36 .Nm pfil_head_unregister ,
39 .Nm pfil_remove_hook ,
41 .Nd packet filter interface
48 .Fn (*pfil_func_t) "void *arg" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
50 .Fn pfil_head_register "struct pfil_head *ph"
52 .Fn pfil_head_unregister "struct pfil_head *pfh"
53 .Ft struct pfil_head *
54 .Fn pfil_head_get "int type" "u_long val"
56 .Fn pfil_add_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph"
58 .Fn pfil_remove_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph"
60 .Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
64 framework allows for a specified function to be invoked for every
65 incoming or outgoing packet for a particular network I/O stream.
66 These hooks may be used to implement a firewall or perform packet
69 Packet filtering points are registered with
70 .Fn pfil_head_register .
71 Filtering points are identified by a key (void *) and a data link type
75 Packet filters use the key and data link type to look up the filtering
76 point with which they register themselves.
77 The key is unique to the filtering point.
78 The data link type is a
80 DLT constant indicating what kind of header is present on the packet
81 at the filtering point.
82 Filtering points may be unregistered with the
83 .Fn pfil_head_unregister
86 Packet filters register/unregister themselves with a filtering point
91 functions, respectively.
92 The head is looked up using the
94 function, which takes the key and data link type that the packet filter
96 Filters may provide an argument to be passed to the filter when
99 When a filter is invoked, the packet appears just as if it
100 .Dq came off the wire .
101 That is, all protocol fields are in network byte order.
102 The filter is called with its specified argument, the pointer to the
103 pointer to the mbuf containing the packet, the pointer to the network
104 interface that the packet is traversing, and the direction
108 see also below) that the packet is traveling.
109 The filter may change which mbuf the mbuf ** argument references.
110 The filter returns an
112 if the packet processing is to stop, or 0 if the processing is to continue.
113 If the packet processing is to stop, it is the responsibility of the
114 filter to free the packet.
118 parameter, used in the
122 functions, indicates when the filter should be called.
124 .Bl -tag -offset indent -width ".Dv PFIL_MPSAFE" -compact
126 call me on incoming packets
128 call me on outgoing packets
130 call me on all of the above
139 interface first appeared in
143 input and output lists were originally implemented as
147 however this was changed in
152 This change was to allow the input and output filters to be processed in
153 reverse order, to allow the same path to be taken, in or out of the kernel.
157 interface was changed in 1.4T to accept a 3rd parameter to both
160 .Fn pfil_remove_hook ,
161 introducing the capability of per-protocol filtering.
162 This was done primarily in order to support filtering of IPv6.
166 framework was changed to work with an arbitrary number of filtering points,
167 as well as be less IP-centric.
171 interface was imported from
175 and was reworked to suit a threaded kernel model in
180 interface was designed and implemented by Matthew R. Green, with help
181 from Darren Reed, Jason R. Thorpe and Charles M. Hannum.
182 Darren Reed added support for IPv6 in addition to IPv4.
183 Jason R. Thorpe added support for multiple hooks and other clean up.