Copyright (c) 1996 Matthew R. Green.
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.Dd August 4, 1996 .Dt PFIL 9 .Os NetBSD .Sh NAME .Nm pfil .Nd packet filter interface .Sh SYNOPSIS .Fd #include <sys/param.h> .Fd #include <netinet/ip.h> .Ft struct packet_filter_hook * .Fn pfil_hook_get int .Ft void .Fn pfil_add_hook "int (*func)()" "int flags" .Ft void .Fn pfil_remove_hook "int (*func)()" "int flags" (void *, int, struct ifnet *, int, struct mbuf **)
.Sh DESCRIPTION The .Nm interface allows a function to be called on every incoming or outgoing packets. The hooks for these are embedded in the .Fn ip_input and .Fn ip_output routines. The .Fn pfil_hook_get function returns the first member of a particular hook, either the in or out list. The .Fn pfil_add_hook function takes a function of the form below as it's first argument, and the flags for which lists to add the function to. The possible values for these flags are some combination of PFIL_IN and PFIL_OUT. The .Fn pfil_remove_hook removes a hook from the specified lists.
p The .Va func argument is a function with the following prototype.
p .Fn func "void *data" "int hlen" "struct ifnet *net" "int dir" "struct mbuf **m"
p The .Va data describes the packet. Currently, this may only be a pointer to a ip structure. The .Va net and .Va m arguments describe the network interface and the mbuf holding data for this packet. The .Va dir is the direction; 0 for incoming packets and 1 for outgoing packets. if the function returns non-zero, this signals an error and no further processing of this packet is performed. The function should set errno to indicate the nature of the error. It is the hook's responsibiliy to free the chain if the packet is being dropped.
p The .Nm interface is enabled in the kernel via the .Sy PFIL_HOOKS option. .Sh RETURN VALUES If successful .Fn pfil_hook_get returns the first member of the packet filter list, .Fn pfil_add_hook and .Fn pfil_remove_hook are expected to always succeed. .Sh HISTORY The .Nm interface first appeared in .Nx 1.3 .Sh BUGS The current .Nm implementation will need changes to suit a threaded kernel model. .Sh SEE ALSO .Xr bpf 4 .
Indexes created Wed Oct 22 13:09:56 GMT 2025