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.\"	$OpenBSD: bpf_mtap.9,v 1.18 2023/04/12 09:55:22 jsg Exp $
.\"
.\" Copyright (c) 2016 David Gwynne <dlg@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.Dd $Mdocdate: April 12 2023 $
.Dt BPF_MTAP 9
.Os
.Sh NAME
.Nm bpfattach ,
.Nm bpfdetach ,
.Nm bpfsattach ,
.Nm bpfsdetach ,
.Nm bpf_filter ,
.Nm bpf_mfilter ,
.Nm bpf_validate ,
.Nm bpf_mtap ,
.Nm bpf_mtap_hdr ,
.Nm bpf_mtap_af ,
.Nm bpf_mtap_ether ,
.Nm bpf_tap_hdr
.Nd BPF kernel API
.Sh SYNOPSIS
.In net/bpf.h
.Ft void
.Fo bpfattach
.Fa "caddr_t *bpfp"
.Fa "struct ifnet *ifp"
.Fa "u_int dlt"
.Fa "u_int hdrlen"
.Fc
.Ft void
.Fn bpfdetach "struct ifnet *ifp"
.Ft void *
.Fn bpfsattach "caddr_t *bpfp" "const char *name" "u_int dlt" "u_int hdrlen"
.Ft void
.Fn bpfsdetach "void *bpfif"
.Ft u_int
.Fo bpf_filter
.Fa "const struct bpf_insn *pc"
.Fa "const u_char *pkt"
.Fa "u_int wirelen"
.Fa "u_int pktlen"
.Fc
.Ft u_int
.Fo bpf_mfilter
.Fa "const struct bpf_insn *pc"
.Fa "const struct mbuf *m"
.Fa "u_int wirelen"
.Fc
.Ft int
.Fn bpf_validate "struct bpf_insn *pc" "int len"
.Ft int
.Fn bpf_mtap "caddr_t bpf" "const struct mbuf *m" "u_int direction"
.Ft int
.Fo bpf_mtap_hdr
.Fa "caddr_t bpf"
.Fa "const void *hdr"
.Fa "u_int hdrlen"
.Fa "const struct mbuf *m"
.Fa "u_int direction"
.Fc
.Ft int
.Fo bpf_mtap_af
.Fa "caddr_t bpf"
.Fa "u_int32_t af"
.Fa "const struct mbuf *m"
.Fa "u_int direction"
.Fc
.Ft int
.Fn bpf_mtap_ether "caddr_t bpf" "const struct mbuf *m" "u_int direction"
.Ft int
.Fo bpf_tap_hdr
.Fa "caddr_t bpf"
.Fa "const void *hdr"
.Fa "u_int hdrlen"
.Fa "const void *buf"
.Fa "u_int buflen"
.Fa "u_int direction"
.Fc
.Sh DESCRIPTION
The BPF kernel API provides functions for evaluating BPF instructions
against packets, and incoming linkage from device drivers.
A packet is parsed by the filters associated with each interface
and, if accepted, stashed into the corresponding buffer.
.Pp
.Fn bpfattach
allocates and configures a BPF interface for use with the network interface
.Fa ifp .
.Fa bpfp
is the location of BPF interface pointer that the network interface passes to
the filter functions.
The BPF interface pointer will be clear until a filter is registered and
packets can be filtered on it.
The
.Fa dlt
argument identifies the data link-layer type that the network
interface provides for this BPF interface.
.Fn bpfattach
may be called multiple times against the same network interface to
provide different data link-layer types for filtering.
.Fa hdrlen
indicates the length of the link header for the data link-layer type.
.Pp
.Fn bpfdetach
removes and frees all the BPF interfaces that were configured for
the network interface
.Fa ifp .
.Pp
.Fn bpfsattach
allocates and configures a BPF interface for use by the subsystem
identified by
.Fa name .
The
.Fa bpfp ,
.Fa dlt ,
.Fa hdrlen
arguments work like those in
.Fn bpfattach .
.Pp
.Fn bpfsdetach
removes and frees the BPF interface referenced by
.Fa bpfif .
.Pp
.Fn bpf_filter
executes the BPF program referenced by
.Fa pc
against the packet buffer starting at
.Fa pkt
of
.Fa pktlen
bytes in length.
.Fa wirelen
is the length of the original packet on the wire.
.Pp
.Fn bpf_mfilter
executes the BPF program referenced by
.Fa pc
against the packet in the mbuf
.Fa m .
.Fa wirelen
is the length of the original packet on the wire.
.Pp
.Fn bpf_validate
tests if the BPF program referenced by
.Fa pc
is valid.
.Fa len
specifies the number of instructions in
.Fa pc .
.Pp
.Fn bpf_tap
runs the filters on the BPF interface referenced by
.Fa bpf
in the direction
.Fa direction
against the packet in the
.Fa pkt
buffer.
.Pp
.Fn bpf_mtap
runs the filters on the BPF interface referenced by
.Fa bpf
in the direction
.Fa direction
against the packet in mbuf chain
.Fa m .
.Pp
.Fn bpf_mtap_hdr
runs the filters on the BPF interface referenced by
.Fa bpf
in the direction
.Fa direction
against the packet in mbuf chain
.Fa m .
The header referenced by
.Fa hdr
will be prefixed to the packet during filter evaluation.
.Pp
.Fn bpf_mtap_af
runs the filters on the BPF interface referenced by
.Fa bpf
in the direction
.Fa direction
against the packet in mbuf chain
.Fa m .
The address family specified by
.Fa af
will be prepended to the packet before matching occurs.
.Pp
.Fn bpf_mtap_ether
runs the filters on the BPF interface referenced by
.Fa bpf
in the direction
.Fa direction
against an Ethernet packet in the mbuf
.Fa m .
If the mbuf is flagged with
.Dv M_VLANTAG ,
an Ethernet VLAN header is constructed using
m->m_pkthdr.ether_vtag
and
m->m_pkthdr.pf.prio
before matching occurs.
.Pp
.Fn bpf_tap_hdr
runs the filters on the BPF interface referenced by
.Fa bpf
in the direction
.Fa direction
against the buffer
.Fa buf
of length
.Fa buflen .
The header
.Fa hdr
of length
.Fa hdrlen
will be prefixed to the buffer for filter evaluation.
.Sh CONTEXT
.Fn bpfattach ,
.Fn bpfdetach ,
.Fn bpfsattach ,
and
.Fn bpfsdetach
can be called from process context.
.Pp
.Fn bpf_filter ,
.Fn bpf_mfilter ,
and
.Fn bpf_validate
can be called from process context, or from an interrupt context.
.Pp
.Fn bpf_mtap ,
.Fn bpf_mtap_hdr ,
.Fn bpf_mtap_af ,
.Fn bpf_mtap_ether ,
and
.Fn bpf_tap_hdr
can be called from process context, or from an interrupt context at or below
.Dv IPL_NET .
.Sh RETURN VALUES
.Fn bpfsattach
returns a reference to the BPF interface it allocates.
.Pp
.Fn bpf_filter
and
.Fn bpf_mfilter
return -1 (cast to an unsigned integer) if the filter program is
.Dv NULL ,
or the result of the filter program.
Filter programs should return the maximum number of bytes of the
packet to capture, or 0 if the packet does not match the filter
program.
.Pp
.Fn bpf_validate
returns a non-zero value if the BPF program is valid,
otherwise 0.
.Pp
.Fn bpf_mtap ,
.Fn bpf_mtap_hdr ,
.Fn bpf_mtap_af ,
.Fn bpf_mtap_ether ,
and
.Fn bpf_tap_hdr
return 1 if the packet or buffer matched a filter that indicates it
should be dropped, otherwise 0.
.Sh SEE ALSO
.Xr mbuf 9 ,
.Xr spl 9