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 .\" This document is derived in part from the enet man page (enet.4)
 .\" distributed with 4.3BSD Unix.
 .\"
-.TH BPF 4  "23 May 1991"
-.SH NAME
-bpf \- Berkeley Packet Filter
-.SH SYNOPSIS
-.B "pseudo-device bpfilter 16"
-.SH DESCRIPTION
+.Dd January 16, 1996
+.Dt BPF 4
+.Os BSD 4.4
+.Sh NAME
+.Nm bpf
+.Nd Berkeley Packet Filter
+.Sh SYNOPSIS
+.Cd pseudo-device bpfilter
+.Sh DESCRIPTION
 The Berkeley Packet Filter
-provides a raw interface to data link layers in a protocol 
+provides a raw interface to data link layers in a protocol
 independent fashion.
 All packets on the network, even those destined for other hosts,
 are accessible through this mechanism.
-.PP
+.Pp
 The packet filter appears as a character special device,
-.I /dev/bpf0, /dev/bpf1,
+.Pa /dev/bpf0 ,
+.Pa /dev/bpf1 ,
 etc.
-After opening the device, the file descriptor must be bound to a 
-specific network interface with the BIOSETIF ioctl.
+After opening the device, the file descriptor must be bound to a
+specific network interface with the
+.Dv BIOSETIF
+ioctl.
 A given interface can be shared be multiple listeners, and the filter
 underlying each descriptor will see an identical packet stream.
-The total number of open 
+The total number of open
 files is limited to the value given in the kernel configuration; the
-example given in the SYNOPSIS above sets the limit to 16.
-.PP
-A separate device file is required for each minor device.  
-If a file is in use, the open will fail and 
-.I errno
-will be set to EBUSY.
-.PP
+example given in the
+.Sx SYNOPSIS
+above sets the limit to 16.
+.Pp
+A separate device file is required for each minor device.
+If a file is in use, the open will fail and
+.Va errno
+will be set to
+.Er EBUSY .
+.Pp
 Associated with each open instance of a
-.I bpf
+.Nm bpf
 file is a user-settable packet filter.
-Whenever a packet is received by an interface, 
+Whenever a packet is received by an interface,
 all file descriptors listening on that interface apply their filter.
-Each descriptor that accepts the packet receives its own copy.
-.PP
+Each descriptor that accepts the packet receives its own copy. 
+.Pp
 Reads from these files return the next group of packets
-that have matched the filter.
+that have matched the filter. 
 To improve performance, the buffer passed to read must be
-the same size as the buffers used internally by 
-.I bpf.
-This size is returned by the BIOCGBLEN ioctl (see below), and under
-BSD, can be set with BIOCSBLEN.
+the same size as the buffers used internally by
+.Nm
+This size is returned by the
+.Dv BIOCGBLEN
+ioctl (see below), and 
+can be set with
+.Dv BIOCSBLEN.
 Note that an individual packet larger than this size is necessarily
 truncated.
-.PP
+.Pp
 The packet filter will support any link level protocol that has fixed length
-headers.  Currently, only Ethernet, SLIP and PPP drivers have been
-modified to interact with
-.I bpf.
-.PP
+headers.  Currently, only Ethernet, 
+.Tn SLIP ,
+and
+.Tn PPP
+drivers have been modified to interact with
+.Nm bpf .
+.Pp
 Since packet data is in network byte order, applications should use the
-.I byteorder(3n)
+.Xr byteorder 3
 macros to extract multi-byte values.
-.PP
-A packet can be sent out on the network by writing to a 
-.I bpf
+.Pp
+A packet can be sent out on the network by writing to a
+.Nm bpf
 file descriptor.  The writes are unbuffered, meaning only one
 packet can be processed per write.
-Currently, only writes to Ethernets and SLIP links are supported.
-.SH IOCTLS
-The 
-.I ioctl
+Currently, only writes to Ethernets and
+.Tn SLIP
+links are supported.  
+.Sh IOCTLS
+The
+.Xr ioctl 2
 command codes below are defined in <net/bpf.h>.  All commands require
 these includes:
-.ft B
-.nf
-
+.Bd -literal
 	#include <sys/types.h>
 	#include <sys/time.h>
 	#include <sys/ioctl.h>
-	#include <net/bpf.h>
-
-.fi
-.ft R
-Additionally, BIOCGETIF and BIOCSETIF require \fB<net/if.h>\fR.
+	#include <net/bpf.h> 
+.Ed
+.Pp
+Additionally, 
+.Dv BIOCGETIF
+and
+.Dv BIOCSETIF
+require
+.Aq Pa net/if.h .
 
-In addition to FIONREAD and SIOCGIFADDR, the following commands
-may be applied to any open
-.I bpf
+In addition to
+.Dv FIONREAD
+and
+.Dv SIOCGIFADDR ,
+the following commands may be applied to any open
+.Nm
 file.
-The (third) argument to the 
-.I ioctl
+The (third) argument to
+.Xr ioctl 2
 should be a pointer to the type indicated.
-.TP 10
-.B BIOCGBLEN (u_int)
+
+.Bl -tag -width BIOCGRTIMEOUT
+.It Dv BIOCGBLEN
+.Pq Li u_int
 Returns the required buffer length for reads on
-.I bpf
+.Nm
 files.
-.TP 10
-.B BIOCSBLEN (u_int)
-Sets the buffer length for reads on 
-.I bpf
+.It Dv BIOCSBLEN
+.Pq Li u_int
+Sets the buffer length for reads on
+.Nm
 files.  The buffer must be set before the file is attached to an interface
-with BIOCSETIF.
+with
+.Dv BIOCSETIF .
 If the requested buffer size cannot be accomodated, the closest
 allowable size will be set and returned in the argument.
-A read call will result in EIO if it is passed a buffer that is not this size.
-.TP 10
-.B BIOCGDLT (u_int)
+A read call will result in 
+.Er EIO
+if it is passed a buffer that is not this size.
+.It Dv BIOCGDLT
+.Pq Li u_int
 Returns the type of the data link layer underyling the attached interface.
-EINVAL is returned if no interface has been specified.
-The device types, prefixed with ``DLT_'', are defined in <net/bpf.h>.
-.TP 10
-.B BIOCPROMISC
+.Er EINVAL
+is returned if no interface has been specified.
+The device types, prefixed with
+.Dq Li DLT_ ,
+are defined in
+.Aq Pa net/bpf.h .
+.It Dv BIOCPROMISC
 Forces the interface into promiscuous mode.
 All packets, not just those destined for the local host, are processed.
 Since more than one file can be listening on a given interface,
 a listener that opened its interface non-promiscuously may receive
-packets promiscuously.  This problem can be remedied with an 
-appropriate filter.
-.IP
-The interface remains in promiscuous mode until all files listening 
-promiscuously are closed.
-.TP 10
-.B BIOCFLUSH
+packets promiscuously.  This problem can be remedied with an
+appropriate filter. 
+.It Dv BIOCFLUSH
 Flushes the buffer of incoming packets,
 and resets the statistics that are returned by BIOCGSTATS.
-.TP 10
-.B BIOCGETIF (struct ifreq)
+.It Dv BIOCGETIF
+.Pq Li "struct ifreq"
 Returns the name of the hardware interface that the file is listening on.
-The name is returned in the if_name field of 
-.I ifr.
+The name is returned in the if_name field of
+the
+.Li ifreq
+structure.
 All other fields are undefined.
-.TP 10
-.B BIOCSETIF (struct ifreq)
+.It Dv BIOCSETIF
+.Pq Li "struct ifreq"
 Sets the hardware interface associate with the file.  This
 command must be performed before any packets can be read.
 The device is indicated by name using the
-.I if_name
-field of the 
-.I ifreq.
-Additionally, performs the actions of BIOCFLUSH.
-.TP 10
-.B BIOCSRTIMEOUT, BIOCGRTIMEOUT (struct timeval)
+.Li if_name
+field of the
+.Li ifreq
+structure.
+Additionally, performs the actions of 
+.Dv BIOCFLUSH .
+.It Dv BIOCSRTIMEOUT
+.It Dv BIOCGRTIMEOUT
+.Pq Li "struct timeval"
 Set or get the read timeout parameter.
-The 
-.I timeval 
+The argument
 specifies the length of time to wait before timing
 out on a read request.
 This parameter is initialized to zero by
-.IR open(2),
+.Xr open 2 ,
 indicating no timeout.
-.TP 10
-.B BIOCGSTATS (struct bpf_stat)
+.It Dv BIOCGSTATS
+.Pq Li "struct bpf_stat"
 Returns the following structure of packet statistics:
-.ft B
-.nf
-
+.Bd -literal
 struct bpf_stat {
 	u_int bs_recv;
 	u_int bs_drop;
 };
-.fi
-.ft R
-.IP
+.Ed
+
 The fields are:
-.RS
-.TP 15
-.I bs_recv
+.Bl -hang -offset indent
+.It Li bs_recv
 the number of packets received by the descriptor since opened or reset
 (including any buffered since the last read call);
-and
-.TP
-.I bs_drop
-the number of packets which were accepted by the filter but dropped by the 
+and 
+.It Li bs_drop
+the number of packets which were accepted by the filter but dropped by the
 kernel because of buffer overflows
 (i.e., the application's reads aren't keeping up with the packet traffic).
-.RE
-.TP 10
-.B BIOCIMMEDIATE (u_int)
+.El
+.It Dv BIOCIMMEDIATE
+.Pq Li u_int
 Enable or disable ``immediate mode'', based on the truth value of the argument.
-When immediate mode is enabled, reads return immediately upon packet 
+When immediate mode is enabled, reads return immediately upon packet
 reception.  Otherwise, a read will block until either the kernel buffer
 becomes full or a timeout occurs.
 This is useful for programs like
-.I rarpd(8c),
+.Xr rarpd 8
 which must respond to messages in real time.
-The default for a new file is off.
-.TP 10
-.B BIOCSETF (struct bpf_program)
-Sets the filter program used by the kernel to discard uninteresting 
+The default for a new file is off. 
+.It Dv BIOCSETF
+.Pq Li "struct bpf_program"
+Sets the filter program used by the kernel to discard uninteresting
 packets.  An array of instructions and its length is passed in using
 the following structure:
-.ft B
-.nf
-
+.Bd -literal
 struct bpf_program {
 	int bf_len;
-	struct bpf_insn *bf_insns;
+	struct bpf_insn *bf_insns; 
 };
-.fi
-.ft R
-.IP
+.Ed
+
 The filter program is pointed to by the
-.I bf_insns
-field while its length in units of `struct bpf_insn' is given by the
-.I bf_len
+.Li bf_insns
+field while its length in units of 
+.Sq Li struct bpf_insn
+is given by the
+.Li bf_len
 field.
-Also, the actions of BIOCFLUSH are performed.
-.IP
-See section \fBFILTER MACHINE\fP for an explanation of the filter language.
-.TP 10
-.B BIOCVERSION (struct bpf_version)
+Also, the actions of
+.Dv BIOCFLUSH are performed.
+See section
+.Sx "FILTER MACHINE"
+for an explanation of the filter language.
+.It Dv BIOCVERSION
+.Pq Li "struct bpf_version"
 Returns the major and minor version numbers of the filter languange currently
 recognized by the kernel.  Before installing a filter, applications must check
 that the current version is compatible with the running kernel.  Version
 numbers are compatible if the major numbers match and the application minor
 is less than or equal to the kernel minor.  The kernel version number is
 returned in the following structure:
-.ft B
-.nf
-
+.Bd -literal
 struct bpf_version {
-	u_short bv_major;
-	u_short bv_minor;
+        u_short bv_major;
+        u_short bv_minor;
 };
-.fi
-.ft R
-.IP
-The current version numbers are given by 
-.B BPF_MAJOR_VERSION
-and 
-.B BPF_MINOR_VERSION
-from <net/bpf.h>.
+.Ed
+
+The current version numbers are given by
+.Dv BPF_MAJOR_VERSION
+and
+.Dv BPF_MINOR_VERSION
+from
+.Aq Pa net/bpf.h .
 An incompatible filter
 may result in undefined behavior (most likely, an error returned by
-.I ioctl()
+.Fn ioctl
 or haphazard packet matching).
-.SH BPF HEADER
-The following structure is prepended to each packet returned by 
-.I read(2):
-.in 15
-.ft B
-.nf
-
+.Sh BPF HEADER
+The following structure is prepended to each packet returned by
+.Xr read 2 :
+.Bd -literal
 struct bpf_hdr {
-	struct timeval bh_tstamp;
-	u_long bh_caplen;
-	u_long bh_datalen;
-	u_short bh_hdrlen;
+        struct timeval bh_tstamp; 
+        u_long bh_caplen;
+        u_long bh_datalen;
+        u_short bh_hdrlen;
 };
-.fi
-.ft R
-.in -15
-.PP
+.Ed
+.Pp
 The fields, whose values are stored in host order, and are:
-.TP 15
-.I bh_tstamp
+.Pp
+.Bl -tag -compact -width bh_datalen
+.It Li bh_tstamp
 The time at which the packet was processed by the packet filter.
-.TP
-.I bh_caplen
+.It Li bh_caplen
 The length of the captured portion of the packet.  This is the minimum of
 the truncation amount specified by the filter and the length of the packet.
-.TP
-.I bh_datalen
+.It Li bh_datalen
 The length of the packet off the wire.
 This value is independent of the truncation amount specified by the filter.
-.TP
-.I bh_hdrlen
-The length of the BPF header, which may not be equal to
-.I sizeof(struct bpf_hdr).
-.RE
-.PP
+.It Li bh_hdrlen
+The length of the
+.Nm
+header, which may not be equal to
+.\" XXX - not really a function call
+.Fn sizeof "struct bpf_hdr" .
+.El
+.Pp
 The 
-.I bh_hdrlen
+.Li bh_hdrlen
 field exists to account for
 padding between the header and the link level protocol.
 The purpose here is to guarantee proper alignment of the packet
 data structures, which is required on alignment sensitive 
 architectures and and improves performance on many other architectures.
 The packet filter insures that the 
-.I bpf_hdr
-and the \fInetwork layer\fR header will be word aligned.  Suitable precautions
+.Li bpf_hdr
+and the network layer
+header will be word aligned.  Suitable precautions
 must be taken when accessing the link layer protocol fields on alignment
 restricted machines.  (This isn't a problem on an Ethernet, since
 the type field is a short falling on an even offset,
 and the addresses are probably accessed in a bytewise fashion).
-.PP
+.Pp
 Additionally, individual packets are padded so that each starts
 on a word boundary.  This requires that an application
 has some knowledge of how to get from packet to packet.
-The macro BPF_WORDALIGN is defined in <net/bpf.h> to facilitate
+The macro
+.Dv BPF_WORDALIGN
+is defined in
+.Aq Pa net/bpf.h
+to facilitate
 this process.  It rounds up its argument
-to the nearest word aligned value (where a word is BPF_ALIGNMENT bytes wide).
-.PP
-For example, if `p' points to the start of a packet, this expression
+to the nearest word aligned value (where a word is
+.Dv BPF_ALIGNMENT
+bytes wide).
+.Pp
+For example, if
+.Sq Li p
+points to the start of a packet, this expression
 will advance it to the next packet:
-.sp
-.RS
-.ce 1
-.nf
-p = (char *)p + BPF_WORDALIGN(p->bh_hdrlen + p->bh_caplen)
-.fi
-.RE
-.PP
+.Dl p = (char *)p + BPF_WORDALIGN(p->bh_hdrlen + p->bh_caplen)
+.Pp
 For the alignment mechanisms to work properly, the
 buffer passed to 
-.I read(2)
+.Xr read 2
 must itself be word aligned.  
-.I malloc(3)
+The
+.Xr malloc 3
+function
 will always return an aligned buffer.
-.ft R
-.SH FILTER MACHINE
+.Sh FILTER MACHINE
 A filter program is an array of instructions, with all branches forwardly
-directed, terminated by a \fBreturn\fP instruction.
+directed, terminated by a 
+.Em return
+instruction.
 Each instruction performs some action on the pseudo-machine state,
 which consists of an accumulator, index register, scratch memory store,
 and implicit program counter.
 
 The following structure defines the instruction format:
-.RS
-.ft B
-.nf
-
+.Bd -literal
 struct bpf_insn {
 	u_short	code;
 	u_char 	jt;
 	u_char 	jf;
 	long k;
 };
-.fi
-.ft R
-.RE
+.Ed
 
-The \fIk\fP field is used in differnet ways by different insutructions, 
-and the \fIjt\fP and \fIjf\fP fields are used as offsets
+The 
+.Li k
+field is used in differnet ways by different insutructions, 
+and the
+.Li jt
+and 
+.Li jf
+fields are used as offsets
 by the branch intructions.
 The opcodes are encoded in a semi-hierarchical fashion.
-There are eight classes of intructions: BPF_LD, BPF_LDX, BPF_ST, BPF_STX,
-BPF_ALU, BPF_JMP, BPF_RET, and BPF_MISC.  Various other mode and 
+There are eight classes of intructions: 
+.Dv BPF_LD , 
+.Dv BPF_LDX ,
+.Dv BPF_ST ,
+.Dv BPF_STX ,
+.Dv BPF_ALU ,
+.Dv BPF_JMP ,
+.Dv BPF_RET ,
+and
+.Dv BPF_MISC .
+Various other mode and 
 operator bits are or'd into the class to give the actual instructions.
-The classes and modes are defined in <net/bpf.h>.
+The classes and modes are defined in
+.Aq Pa net/bpf.h .
 
-Below are the semantics for each defined BPF instruction.
+Below are the semantics for each defined
+.Nm
+instruction.
 We use the convention that A is the accumulator, X is the index register,
 P[] packet data, and M[] scratch memory store.
 P[i:n] gives the data at byte offset ``i'' in the packet,
 interpreted as a word (n=4),
 unsigned halfword (n=2), or unsigned byte (n=1).
 M[i] gives the i'th word in the scratch memory store, which is only
-addressed in word units.  The memory store is indexed from 0 to BPF_MEMWORDS-1.
-\fIk\fP, \fIjt\fP, and \fIjf\fP are the corresponding fields in the
+addressed in word units.  The memory store is indexed from 0 to 
+.Dv BPF_MEMWORDS
+- 1.
+.Li k ,
+.Li jt ,
+and
+.Li jf
+are the corresponding fields in the
 instruction definition.  ``len'' refers to the length of the packet.
-
-.TP 10
-.B BPF_LD
+.Pp
+.Bl -tag -width BPF_STXx -compact
+.It Dv BPF_LD
 These instructions copy a value into the accumulator.  The type of the
 source operand is specified by an ``addressing mode'' and can be 
-a constant (\fBBPF_IMM\fP), packet data at a fixed offset (\fBBPF_ABS\fP), 
-packet data at a variable offset (\fBBPF_IND\fP), the packet length
-(\fBBPF_LEN\fP),
-or a word in the scratch memory store (\fBBPF_MEM\fP).
-For \fBBPF_IND\fP and \fBBPF_ABS\fP, the data size must be specified as a word
-(\fBBPF_W\fP), halfword (\fBBPF_H\fP), or byte (\fBBPF_B\fP).
-The semantics of all the recognized BPF_LD instructions follow.
-
-.RS
-.TP 30
-.B BPF_LD+BPF_W+BPF_ABS
+a constant
+.Pq Dv BPF_IMM ,
+packet data at a fixed offset
+.Pq Dv BPF_ABS ,
+packet data at a variable offset
+.Pq Dv BPF_IND ,
+the packet length
+.Pq Dv BPF_LEN ,
+or a word in the scratch memory store
+.Pq Dv BPF_MEM .
+For 
+.Dv BPF_IND
+and
+.Dv BPF_ABS,
+the data size must be specified as a word
+.Pq Dv BPF_W ,
+halfword
+.Pq Dv BPF_H ,
+or byte
+.Pq Dv BPF_B .
+The semantics of all the recognized 
+.Dv BPF_LD
+instructions follow.
+.Pp
+.Bl -tag -width "BPF_LD+BPF_W+BPF_IND" -compact
+.It Li BPF_LD+BPF_W+BPF_ABS
 A <- P[k:4]
-.TP
-.B BPF_LD+BPF_H+BPF_ABS
+.It Li BPF_LD+BPF_H+BPF_ABS
 A <- P[k:2]
-.TP
-.B BPF_LD+BPF_B+BPF_ABS
+.It Li BPF_LD+BPF_B+BPF_ABS
 A <- P[k:1]
-.TP
-.B BPF_LD+BPF_W+BPF_IND
+.It Li BPF_LD+BPF_W+BPF_IND
 A <- P[X+k:4]
-.TP
-.B BPF_LD+BPF_H+BPF_IND
+.It Li BPF_LD+BPF_H+BPF_IND
 A <- P[X+k:2]
-.TP
-.B BPF_LD+BPF_B+BPF_IND
+.It Li BPF_LD+BPF_B+BPF_IND
 A <- P[X+k:1]
-.TP
-.B BPF_LD+BPF_W+BPF_LEN
+.It Li BPF_LD+BPF_W+BPF_LEN
 A <- len
-.TP
-.B BPF_LD+BPF_IMM
+.It Li BPF_LD+BPF_IMM
 A <- k
-.TP
-.B BPF_LD+BPF_MEM
+.It Li BPF_LD+BPF_MEM
 A <- M[k]
-.RE
+.El
 
-.TP 10
-.B BPF_LDX
+.It Dv BPF_LDX
 These instructions load a value into the index register.  Note that
 the addressing modes are more retricted than those of the accumulator loads,
 but they include
-.B BPF_MSH,
+.Dv BPF_MSH ,
 a hack for efficiently loading the IP header length.
-.RS
-.TP 30
-.B BPF_LDX+BPF_W+BPF_IMM
+
+.Bl -tag -width "BPF_LDX+BPF_W+BPF_MEM" -compact
+.It Li BPF_LDX+BPF_W+BPF_IMM
 X <- k
-.TP
-.B BPF_LDX+BPF_W+BPF_MEM
+.It Li BPF_LDX+BPF_W+BPF_MEM
 X <- M[k]
-.TP
-.B BPF_LDX+BPF_W+BPF_LEN
+.It Li BPF_LDX+BPF_W+BPF_LEN
 X <- len
-.TP
-.B BPF_LDX+BPF_B+BPF_MSH
+.It Li BPF_LDX+BPF_B+BPF_MSH
 X <- 4*(P[k:1]&0xf)
-.RE
+.El
 
-.TP 10
-.B BPF_ST
+.It Dv BPF_ST
 This instruction stores the accumulator into the scratch memory.
 We do not need an addressing mode since there is only one possibility
 for the destination.
-.RS
-.TP 30
-.B BPF_ST
+
+.Bl -tag -width "BPF_ST" -compact
+.It Li BPF_ST
 M[k] <- A
-.RE
+.El
 
-.TP 10
-.B BPF_STX
+.It Dv BPF_STX
 This instruction stores the index register in the scratch memory store.
-.RS
-.TP 30
-.B BPF_STX
+
+.Bl -tag -width "BPF_STX" -compact
+.It Li BPF_STX
 M[k] <- X
-.RE
+.El
 
-.TP 10
-.B BPF_ALU
+.It Dv BPF_ALU
 The alu instructions perform operations between the accumulator and
 index register or constant, and store the result back in the accumulator.
-For binary operations, a source mode is required (\fBBPF_K\fP or 
-\fBBPF_X\fP).
-.RS
-.TP 30
-.B BPF_ALU+BPF_ADD+BPF_K
+For binary operations, a source mode is required 
+.Po
+.Dv BPF_K
+or
+.Dv BPF_X
+.Pc .
+
+.Bl -tag -width "BPF_ALU+BPF_MUL+BPF_K" -compact
+.It Li BPF_ALU+BPF_ADD+BPF_K
 A <- A + k
-.TP
-.B BPF_ALU+BPF_SUB+BPF_K
+.It Li BPF_ALU+BPF_SUB+BPF_K
 A <- A - k
-.TP
-.B BPF_ALU+BPF_MUL+BPF_K
+.It Li BPF_ALU+BPF_MUL+BPF_K
 A <- A * k
-.TP
-.B BPF_ALU+BPF_DIV+BPF_K
+.It Li BPF_ALU+BPF_DIV+BPF_K
 A <- A / k
-.TP
-.B BPF_ALU+BPF_AND+BPF_K
+.It Li BPF_ALU+BPF_AND+BPF_K
 A <- A & k
-.TP
-.B BPF_ALU+BPF_OR+BPF_K
+.It Li BPF_ALU+BPF_OR+BPF_K
 A <- A | k
-.TP
-.B BPF_ALU+BPF_LSH+BPF_K
+.It Li BPF_ALU+BPF_LSH+BPF_K
 A <- A << k
-.TP
-.B BPF_ALU+BPF_RSH+BPF_K
+.It Li BPF_ALU+BPF_RSH+BPF_K
 A <- A >> k
-.TP
-.B BPF_ALU+BPF_ADD+BPF_X
+.It Li BPF_ALU+BPF_ADD+BPF_X
 A <- A + X
-.TP
-.B BPF_ALU+BPF_SUB+BPF_X
+.It Li BPF_ALU+BPF_SUB+BPF_X
 A <- A - X
-.TP
-.B BPF_ALU+BPF_MUL+BPF_X
+.It Li BPF_ALU+BPF_MUL+BPF_X
 A <- A * X
-.TP
-.B BPF_ALU+BPF_DIV+BPF_X
+.It Li BPF_ALU+BPF_DIV+BPF_X
 A <- A / X
-.TP
-.B BPF_ALU+BPF_AND+BPF_X
+.It Li BPF_ALU+BPF_AND+BPF_X
 A <- A & X
-.TP
-.B BPF_ALU+BPF_OR+BPF_X
+.It Li BPF_ALU+BPF_OR+BPF_X
 A <- A | X
-.TP
-.B BPF_ALU+BPF_LSH+BPF_X
+.It Li BPF_ALU+BPF_LSH+BPF_X
 A <- A << X
-.TP
-.B BPF_ALU+BPF_RSH+BPF_X
+.It Li BPF_ALU+BPF_RSH+BPF_X
 A <- A >> X
-.TP
-.B BPF_ALU+BPF_NEG
+.It Li BPF_ALU+BPF_NEG
 A <- -A
-.RE
+.El
 
-.TP 10
-.B BPF_JMP
+.It Dv BPF_JMP
 The jump instructions alter flow of control.  Conditional jumps
-compare the accumulator against a constant (\fBBPF_K\fP) or 
-the index register (\fBBPF_X\fP).  If the result is true (or non-zero),
+compare the accumulator against a constant
+.Pq Dv BPF_K
+or the index register
+.Pq Dv BPF_X .
+If the result is true (or non-zero),
 the true branch is taken, otherwise the false branch is taken.
 Jump offsets are encoded in 8 bits so the longest jump is 256 instructions.
-However, the jump always (\fBBPF_JA\fP) opcode uses the 32 bit \fIk\fP 
+However, the jump always
+.Pq Dv BPF_JA
+opcode uses the 32 bit
+.Li k 
 field as the offset, allowing arbitrarily distant destinations.
 All conditionals use unsigned comparison conventions.
-.RS
-.TP 30
-.B BPF_JMP+BPF_JA
+
+.Bl -tag -width "BPF_JMP+BPF_KSET+BPF_X" -compact
+.It Li BPF_JMP+BPF_JA
 pc += k
-.TP
-.B BPF_JMP+BPF_JGT+BPF_K
+.It Li BPF_JMP+BPF_JGT+BPF_K
 pc += (A > k) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JGE+BPF_K
+.It Li BPF_JMP+BPF_JGE+BPF_K
 pc += (A >= k) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JEQ+BPF_K
+.It Li BPF_JMP+BPF_JEQ+BPF_K
 pc += (A == k) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JSET+BPF_K
+.It Li BPF_JMP+BPF_JSET+BPF_K
 pc += (A & k) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JGT+BPF_X
+.It Li BPF_JMP+BPF_JGT+BPF_X
 pc += (A > X) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JGE+BPF_X
+.It Li BPF_JMP+BPF_JGE+BPF_X
 pc += (A >= X) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JEQ+BPF_X
+.It Li BPF_JMP+BPF_JEQ+BPF_X
 pc += (A == X) ? jt : jf
-.TP
-.B BPF_JMP+BPF_JSET+BPF_X
+.It Li BPF_JMP+BPF_JSET+BPF_X
 pc += (A & X) ? jt : jf
-.RE
-.TP 10
-.B BPF_RET
+.El
+
+.It Dv BPF_RET
 The return instructions terminate the filter program and specify the amount
 of packet to accept (i.e., they return the truncation amount).  A return
 value of zero indicates that the packet should be ignored.
-The return value is either a constant (\fBBPF_K\fP) or the accumulator
-(\fBBPF_A\fP).
-.RS
-.TP 30
-.B BPF_RET+BPF_A
+The return value is either a constant
+.Pq Dv BPF_K
+or the accumulator
+.Pq Dv BPF_A .
+
+.Bl -tag -width "BPF_RET+BPF_K" -compact
+.It Li BPF_RET+BPF_A
 accept A bytes
-.TP
-.B BPF_RET+BPF_K
+.It Li BPF_RET+BPF_K
 accept k bytes
-.RE
-.TP 10
-.B BPF_MISC
+.El
+
+.It Dv BPF_MISC
 The miscellaneous category was created for anything that doesn't
 fit into the above classes, and for any new instructions that might need to
 be added.  Currently, these are the register transfer intructions
 that copy the index register to the accumulator or vice versa.
-.RS
-.TP 30
-.B BPF_MISC+BPF_TAX
+
+.Bl -tag -width "BPF_MISC+BPF_TAX" -compact
+.It Li BPF_MISC+BPF_TAX
 X <- A
-.TP
-.B BPF_MISC+BPF_TXA
+.It Li BPF_MISC+BPF_TXA
 A <- X
-.RE
-.PP
-The BPF interface provides the following macros to facilitate 
+.El
+.Pp
+The
+.Nm
+interface provides the following macros to facilitate 
 array initializers:
-.RS
-\fBBPF_STMT\fI(opcode, operand)\fR
-.br
+.Fn BPF_STMT opcode operand
 and 
-.br
-\fBBPF_JUMP\fI(opcode, operand, true_offset, false_offset)\fR
-.RE
-.PP
-.SH EXAMPLES
+.Fn BPF_JUMP opcode operand true_offset false_offset .
+.Pp
+.Sh EXAMPLES
 The following filter is taken from the Reverse ARP Daemon.  It accepts
 only Reverse ARP requests.
-.RS
-.nf
-
+.Bd -literal
 struct bpf_insn insns[] = {
 	BPF_STMT(BPF_LD+BPF_H+BPF_ABS, 12),
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ETHERTYPE_REVARP, 0, 3),
@@ -602,14 +628,11 @@ struct bpf_insn insns[] = {
 		 sizeof(struct ether_header)),
 	BPF_STMT(BPF_RET+BPF_K, 0),
 };
-.fi
-.RE
-.PP
+.Ed
+.Pp
 This filter accepts only IP packets between host 128.3.112.15 and
 128.3.112.35.
-.RS
-.nf
-
+.Bd -literal
 struct bpf_insn insns[] = {
 	BPF_STMT(BPF_LD+BPF_H+BPF_ABS, 12),
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ETHERTYPE_IP, 0, 8),
@@ -623,16 +646,15 @@ struct bpf_insn insns[] = {
 	BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 	BPF_STMT(BPF_RET+BPF_K, 0),
 };
-.fi
-.RE
-.PP
+.Ed
+.Pp
 Finally, this filter returns only TCP finger packets.  We must parse
-the IP header to reach the TCP header.  The \fBBPF_JSET\fP instruction
+the IP header to reach the TCP header.  The 
+.Dv BPF_JSET
+instruction
 checks that the IP fragment offset is 0 so we are sure
 that we have a TCP header.
-.RS
-.nf
-
+.Bd -literal
 struct bpf_insn insns[] = {
 	BPF_STMT(BPF_LD+BPF_H+BPF_ABS, 12),
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ETHERTYPE_IP, 0, 10),
@@ -648,38 +670,49 @@ struct bpf_insn insns[] = {
 	BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 	BPF_STMT(BPF_RET+BPF_K, 0),
 };
-.fi
-.RE
-.SH SEE ALSO
-tcpdump(1)
-.LP
-McCanne, S., Jacobson V.,
-.RI ` "An efficient, extensible, and portable network monitor" '
-.SH FILES
-/dev/bpf0, /dev/bpf1, ...
-.SH BUGS
-The read buffer must be of a fixed size (returned by the BIOCGBLEN ioctl).
-.PP
+.Ed
+.Sh SEE ALSO
+.Xr tcpdump 1 ,
+.Xr ioctl 2
+.Rs
+.%A McCanne, S.
+.%A Jacobson V.
+.%T "An efficient, extensible, and portable network monitor"
+.Re
+.Sh FILES
+.Bl -tag -compact -width /dev/bpfXXX
+.It Pa /dev/bpf Ns Sy n
+the packet filter device
+.El
+.Sh BUGS
+The read buffer must be of a fixed size (returned by the 
+.Dv BIOCGBLEN
+ioctl).
+.Pp
 A file that does not request promiscuous mode may receive promiscuously
 received packets as a side effect of another file requesting this
 mode on the same hardware interface.  This could be fixed in the kernel
 with additional processing overhead.  However, we favor the model where 
 all files must assume that the interface is promiscuous, and if 
 so desired, must utilize a filter to reject foreign packets.
-.PP
+.Pp
 Data link protocols with variable length headers are not currently supported.
-.PP
-Under SunOS, if a BPF application reads more than 2^31 bytes of
-data, read will fail in EINVAL.  You can either fix the bug in SunOS,
-or lseek to 0 when read fails for this reason.
-.SH HISTORY
-.PP
+.Sh HISTORY
+.Pp
 The Enet packet filter was created in 1980 by Mike Accetta and
 Rick Rashid at Carnegie-Mellon University.  Jeffrey Mogul, at
 Stanford, ported the code to BSD and continued its development from 
 1983 on.  Since then, it has evolved into the Ultrix Packet Filter
-at DEC, a STREAMS NIT module under SunOS 4.1, and BPF.
-.SH AUTHORS
-.PP
+at
+.Tn DEC ,
+a
+.Tn STREAMS
+.Tn NIT
+module under
+.Tn SunOS 4.1 ,
+and
+.Tn BPF .
+.Sh AUTHORS
+.Pp
 Steven McCanne, of Lawrence Berkeley Laboratory, implemented BPF in
 Summer 1990.  Much of the design is due to Van Jacobson.