FreeBSD/Linux Kernel Cross Reference
sys/modules/netgraph/bpf/ng_bpf.4

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    .\" Author: Archie Cobbs <archie@freebsd.org>
    .\"
    .\" $FreeBSD$
    .\" $Whistle: ng_bpf.8,v 1.2 1999/12/03 01:57:12 archie Exp $
    .\"
    .Dd December 2, 1999
    .Dt NG_BPF 4
    .Os FreeBSD 4.0
    .Sh NAME
    .Nm ng_bpf
    .Nd Berkeley packet filter netgraph node type
    .Sh SYNOPSIS
    .Fd #include <net/bpf.h>
    .Fd #include <netgraph/ng_bpf.h>
    .Sh DESCRIPTION
    The
    .Nm bpf
    node type allows Berkeley Packet Filter (see
    .Xr bpf 8 )
    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
    .Xf bpf 8
    filter program which is applied to incoming data only, a destination hook
    for matching packets, a destination hook for non-matching packets,
    and various statistics counters.
    .Pp
    A
    .Xr bpf 8
    program returns an unsigned integer, which is normally interpreted as
    the length of the prefix of the packet to return.  In the context 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 truncated
    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.
    .Pp
    New hooks are initially configured to drop all packets.
    A new filter may be installed using the
    .Dv NGM_BPF_SET_FILTER
    control message.
    .Sh HOOKS
    This node type supports any number of hooks having arbitrary names.
    .Sh CONTROL MESSAGES
    This node type supports the generic control messages, plus the following:
    .Bl -tag -width foo
    .It Dv NGM_BPF_SET_FILTER
    This command sets the filter program that will be applied to incoming
    data on a hook.  The following structure must be supplied as an argument:
    .Bd -literal -offset 4n
    struct ngm_bpf_hookprog {
      char            thisHook[NG_HOOKLEN+1];   /* name of hook */
      char            ifMatch[NG_HOOKLEN+1];    /* match dest hook */
      char            ifNotMatch[NG_HOOKLEN+1]; /* !match dest hook */
      int32_t         bpf_prog_len;             /* #isns in program */
      struct bpf_insn bpf_prog[0];              /* bpf program */
    };
    .Ed
    .Pp
    The hook to be updated is specified in
    .Dv thisHook .
    The BPF program is the sequence of instructions in the
    .Dv bpf_prog
    array; there must be
    .Dv bpf_prog_len
    of them.
   Matching and non-matching incoming packets are delivered out the hooks named
   .Dv ifMatch
   and
   .Dv ifNotMatch ,
   respectively.  The program must be a valid
   .Xr bpf 8
   program or else
   .Er EINVAL
   is returned.
   .It Dv NGM_BPF_GET_FILTER
   This command takes an ASCII string argument, the hook name, and returns the
   corresponding
   .Dv "struct ngm_bpf_hookprog"
   as shown above.
   .It Dv NGM_BPF_GET_STATS
   This command takes an ASCII string argument, the hook name, and returns the
   statistics associated with the hook as a
   .Dv "struct ng_bpf_hookstat" .
   .It Dv NGM_BPF_CLR_STATS
   This command takes an ASCII string argument, the hook name, and clears the
   statistics associated with the hook.
   .It Dv NGM_BPF_GETCLR_STATS
   This command is identical to
   .Dv NGM_BPF_GET_STATS ,
   except that the statistics are also atomically cleared.
   .El
   .Sh SHUTDOWN
   This node shuts down upon receipt of a
   .Dv NGM_SHUTDOWN
   control message, or when all hooks have been disconnected.
   .Sh BUGS
   When built as a loadable kernel module, this module includes the file
   .Dv "net/bpf_filter.c" .
   Although loading the module should fail if
   .Dv "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.
   .Sh SEE ALSO
   .Xr netgraph 4 ,
   .Xr bpf 4 ,
   .Xr ngctl 8
   .Sh AUTHOR
   Archie Cobbs <archie@freebsd.org>

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