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ng_bpf (4)
  • >> ng_bpf (4) ( FreeBSD man: Специальные файлы /dev/* )

  • BSD mandoc
     

    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 destination hook for non-matching packets, and various statistics counters.

    A bpf(4) 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.

    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 incoming 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 respectively. The program must be a valid bpf(4) program or else Er 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 statistics 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"
    
    cat > /tmp/bpf.awk << xxENDxx
    {
      if (!init) {
        printf "bpf_prog_len=%d bpf_prog=[", \$1;
        init=1;
      } else {
        printf " { code=%d jt=%d jf=%d k=%d }", \$1, \$2, \$3, \$4;
      }
    }
    END {
      print " ]"
    }
    xxENDxx
    
    BPFPROG=`tcpdump -s 8192 -ddd ${PATTERN} | awk -f /tmp/bpf.awk`
    
    ngctl msg ${NODEPATH} setprogram { thisHook=\"${INHOOK}\" \
      ifMatch=\"${MATCHHOOK}\" \
      ifNotMatch=\"${NOTMATCHHOOK}\" \
      ${BPFPROG} }
    
     

    SEE ALSO

    bpf(4), netgraph(4), ngctl(8)  

    HISTORY

    The node type was implemented in Fx 4.0 .  

    AUTHORS

    An Archie Cobbs Aq 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.


     

    Index

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


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