1 .\" $NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $
2 .\" $DragonFly: src/share/man/man9/pfil.9,v 1.4 2007/06/30 19:03:52 swildner Exp $
4 .\" Copyright (c) 1996 Matthew R. Green
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30 .Dd September 26, 2005
35 .Nm pfil_head_register ,
36 .Nm pfil_head_unregister ,
40 .Nm pfil_remove_hook ,
42 .Nd packet filter interface
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"
54 .Ft struct packet_filter_hook *
55 .Fn pfil_hook_get "int dir" "struct pfil_head *ph"
57 .Fn pfil_add_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *ph"
59 .Fn pfil_remove_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *ph"
61 .Fn (*func) "void *arg" "struct mbuf **mp" "struct ifnet *" "int dir"
63 .Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
67 framework allows for a specified function to be invoked for every
68 incoming or outgoing packet for a particular network I/O stream.
69 These hooks may be used to implement a firewall or perform packet
72 Packet filtering points are registered with
73 .Fn pfil_head_register .
74 Filtering points are identified by a key (void *) and a data link type
78 Packet filters use the key and data link type to look up the filtering
79 point with which they register themselves.
80 The key is unique to the filtering point.
81 The data link type is a
83 DLT constant indicating what kind of header is present on the packet
84 at the filtering point.
85 Filtering points may be unregistered with the
86 .Fn pfil_head_unregister
89 Packet filters register/unregister themselves with a filtering point
94 functions, respectively.
95 The head is looked up using the
97 function, which takes the key and data link type that the packet filter
99 Filters may provide an argument to be passed to the filter when
102 When a filter is invoked, the packet appears just as if it
103 .Dq came off the wire .
104 That is, all protocol fields are in network byte order.
105 The filter is called with its specified argument, the pointer to the
106 pointer to the mbuf containing the packet, the pointer to the network
107 interface that the packet is traversing, and the direction
111 see also below) that the packet is traveling.
112 The filter may change which mbuf the mbuf ** argument references.
113 The filter returns an
115 if the packet processing is to stop, or 0 if the processing is to continue.
116 If the packet processing is to stop, it is the responsibility of the
117 filter to free the packet.
121 parameter, used in the
125 functions, indicates when the filter should be called.
127 .Bl -tag -offset indent -width PFIL_WAITOK -compact
129 call me on incoming packets
131 call me on outgoing packets
133 call me on all of the above
135 OK to call kmalloc with M_WAITOK.
140 interface is enabled in the kernel via the
148 interface first appeared in
152 input and output lists were originally implemented as
156 however this was changed in
161 This change was to allow the input and output filters to be processed in
162 reverse order, to allow the same path to be taken, in or out of the kernel.
166 interface was changed in 1.4T to accept a 3rd parameter to both
169 .Fn pfil_remove_hook ,
170 introducing the capability of per-protocol filtering.
171 This was done primarily in order to support filtering of IPv6.
175 framework was changed to work with an arbitrary number of filtering points,
176 as well as be less IP-centric.
180 interface was imported from
187 interface was designed and implemented by Matthew R. Green, with help
188 from Darren Reed, Jason R. Thorpe and Charles M. Hannum.
189 Darren Reed added support for IPv6 in addition to IPv4.
190 Jason R. Thorpe added support for multiple hooks and other clean up.
194 implementation will need changes to suit a threaded kernel model.