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NG_BPF(4)	       FreeBSD Kernel Interfaces Manual		     NG_BPF(4)

NAME
     ng_bpf -- Berkeley	packet filter netgraph node type

SYNOPSIS
     #include <sys/types.h>
     #include <net/bpf.h>
     #include <netgraph.h>
     #include <netgraph/ng_bpf.h>

DESCRIPTION
     The bpf node type allows Berkeley Packet Filter (see bpf(4)) filters to
     be	applied	to data	travelling through a Netgraph network.	Each node
     allows an arbitrary number	of connections to arbitrarily named hooks.
     With each hook is associated a bpf(4) filter program which	is applied to
     incoming data only, a destination hook for	matching packets, a destina-
     tion hook for non-matching	packets, and various statistics	counters.

     A bpf(4) program returns an unsigned integer, which is normally inter-
     preted as the length of the prefix	of the packet to return.  In the con-
     text of this node type, returning zero is considered a non-match, in
     which case	the entire packet is delivered out the non-match destination
     hook.  Returning a	value greater than zero	causes the packet to be	trun-
     cated to that length and delivered	out the	match destination hook.
     Either or both destination	hooks may be the empty string, or may not
     exist, in which case the packet is	dropped.

     New hooks are initially configured	to drop	all packets.  A	new filter
     program may be installed using the	NGM_BPF_SET_PROGRAM control message.

HOOKS
     This node type supports any number	of hooks having	arbitrary names.

CONTROL	MESSAGES
     This node type supports the generic control messages, plus	the following:

     NGM_BPF_SET_PROGRAM
	  This command sets the	filter program that will be applied to incom-
	  ing data on a	hook.  The following structure must be supplied	as an
	  argument:

	      struct ng_bpf_hookprog {
		char		thisHook[NG_HOOKSIZ];	  /* name of hook */
		char		ifMatch[NG_HOOKSIZ];	  /* match dest	hook */
		char		ifNotMatch[NG_HOOKSIZ];	  /* !match dest hook */
		int32_t		bpf_prog_len;		  /* #isns in program */
		struct bpf_insn	bpf_prog[];		  /* bpf program */
	      };

	  The hook to be updated is specified in thisHook.  The	BPF program is
	  the sequence of instructions in the bpf_prog array; there must be
	  bpf_prog_len of them.	 Matching and non-matching incoming packets
	  are delivered	out the	hooks named ifMatch and	ifNotMatch, respec-
	  tively.  The program must be a valid bpf(4) program or else EINVAL
	  is returned.

     NGM_BPF_GET_PROGRAM
	  This command takes an	ASCII string argument, the hook	name, and
	  returns the corresponding struct ng_bpf_hookprog as shown above.

     NGM_BPF_GET_STATS
	  This command takes an	ASCII string argument, the hook	name, and
	  returns the statistics associated with the hook as a struct
	  ng_bpf_hookstat.

     NGM_BPF_CLR_STATS
	  This command takes an	ASCII string argument, the hook	name, and
	  clears the statistics	associated with	the hook.

     NGM_BPF_GETCLR_STATS
	  This command is identical to NGM_BPF_GET_STATS, except that the sta-
	  tistics are also atomically cleared.

SHUTDOWN
     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when all hooks have been disconnected.

EXAMPLES
     It	is possible to configure a node	from the command line, using
     tcpdump(1)	to generate raw	BPF instructions which are then	fed into an
     awk(1) script to create the ASCII form of a NGM_BPF_SET_PROGRAM control
     message, as demonstrated here:

	 #!/bin/sh

	 PATTERN="tcp dst port 80"
	 NODEPATH="my_node:"
	 INHOOK="hook1"
	 MATCHHOOK="hook2"
	 NOTMATCHHOOK="hook3"

	 BPFPROG=$( tcpdump -s 8192 -ddd ${PATTERN} | \
		    ( read len ; \
		      echo -n "bpf_prog_len=$len" ; \
		      echo -n "bpf_prog=[" ; \
		      while read code jt jf k ;	do \
			  echo -n " { code=$code jt=$jt	jf=$jf k=$k }" ; \
		      done ; \
		      echo " ]"	) )

	 ngctl msg ${NODEPATH} setprogram { thisHook=\"${INHOOK}\" \
	   ifMatch=\"${MATCHHOOK}\" \
	   ifNotMatch=\"${NOTMATCHHOOK}\" \
	   ${BPFPROG} }

SEE ALSO
     bpf(4), netgraph(4), ngctl(8)

HISTORY
     The ng_bpf	node type was implemented in FreeBSD 4.0.

AUTHORS
     Archie Cobbs <archie@FreeBSD.org>

BUGS
     When built	as a loadable kernel module, this module includes the file
     net/bpf_filter.c.	Although loading the module should fail	if
     net/bpf_filter.c already exists in	the kernel, currently it does not, and
     the duplicate copies of the file do not interfere.	 However, this may
     change in the future.

FreeBSD	9.2			 May 30, 2007			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | HOOKS | CONTROL MESSAGES | SHUTDOWN | EXAMPLES | SEE ALSO | HISTORY | AUTHORS | BUGS

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