bpf(4): assorted markup tweaks
This is mostly non-controversial changes to the cargo-culted markup. While here - add missing .It to BIOCLOCK so that it's not buried in the text for the previous item and comment out a paragraph about an ancient SunOS bug.
This commit is contained in:
uwe
parent
b089952b65
commit
7bd77f6ba6
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@ -1,6 +1,6 @@
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.\" -*- nroff -*-
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.\"
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.\" $NetBSD: bpf.4,v 1.66 2023/02/07 01:17:41 gutteridge Exp $
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.\" $NetBSD: bpf.4,v 1.67 2023/02/11 02:52:52 uwe Exp $
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.\"
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.\" Copyright (c) 1990, 1991, 1992, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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@ -100,12 +100,12 @@ require
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The (third) argument to the
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.Xr ioctl 2
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should be a pointer to the type indicated.
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.Bl -tag -width indent -offset indent
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.It Dv BIOCGBLEN ( u_int )
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.Bl -tag -width Dv
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.It Dv BIOCGBLEN Pq Vt u_int
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Returns the required buffer length for reads on
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.Nm
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files.
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.It Dv BIOCSBLEN ( u_int )
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.It Dv BIOCSBLEN Pq Vt u_int
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Sets the buffer length for reads on
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.Nm
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files.
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@ -116,15 +116,15 @@ allowable size will be set and returned in the argument.
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A read call will result in
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.Er EINVAL
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if it is passed a buffer that is not this size.
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.It Dv BIOCGDLT ( u_int )
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.It Dv BIOCGDLT Pq Vt u_int
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Returns the type of the data link layer underlying the attached interface.
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.Er EINVAL
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is returned if no interface has been specified.
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The device types, prefixed with
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.Dq DLT_ ,
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.Ql DLT_ ,
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are defined in
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.In net/bpf.h .
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.It Dv BIOCGDLTLIST ( struct bpf_dltlist )
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.It Dv BIOCGDLTLIST Pq Vt struct bpf_dltlist
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Returns an array of the available types of the data link layer
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underlying the attached interface:
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.Bd -literal -offset indent
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@ -135,26 +135,29 @@ struct bpf_dltlist {
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.Ed
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.Pp
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The available types are returned in the array pointed to by the
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.Va bfl_list
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field while their length in u_int is supplied to the
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.Va bfl_len
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.Fa bfl_list
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field while their length in
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.Vt u_int
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is supplied to the
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.Fa bfl_len
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field.
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.Er ENOMEM
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is returned if there is not enough buffer space and
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.Er EFAULT
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is returned if a bad address is encountered.
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The
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.Va bfl_len
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.Fa bfl_len
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field is modified on return to indicate the actual length in u_int
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of the array returned.
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If
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.Va bfl_list
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.Fa bfl_list
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is
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.Dv NULL ,
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the
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.Va bfl_len
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field is set to indicate the required length of an array in u_int.
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.It Dv BIOCSDLT ( u_int )
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.Fa bfl_len
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field is set to indicate the required length of an array in
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.Vt u_int .
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.It Dv BIOCSDLT Pq Vt u_int
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Changes the type of the data link layer underlying the attached interface.
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.Er EINVAL
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is returned if no interface has been specified or the specified
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@ -173,30 +176,34 @@ promiscuously are closed.
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Flushes the buffer of incoming packets,
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and resets the statistics that are returned by
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.Dv BIOCGSTATS .
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.It Dv BIOCGETIF ( struct ifreq )
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.It Dv BIOCGETIF Pq Vt struct ifreq
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Returns the name of the hardware interface that the file is listening on.
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The name is returned in the ifr_name field of
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.Fa ifr .
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The name is returned in the
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.Fa ifr_name
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field of
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.Vt ifreq .
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All other fields are undefined.
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.It Dv BIOCSETIF ( struct ifreq )
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.It Dv BIOCSETIF Pq Vt struct ifreq
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Sets the hardware interface associated with the file.
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This command must be performed before any packets can be read.
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The device is indicated by name using the
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.Dv ifr_name
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.Fa ifr_name
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field of the
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.Fa ifreq .
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.Vt ifreq .
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Additionally, performs the actions of
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.Dv BIOCFLUSH .
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.It Dv BIOCSRTIMEOUT , BIOCGRTIMEOUT ( struct timeval )
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Sets or gets the read timeout parameter.
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.It Dv BIOCSRTIMEOUT , BIOCGRTIMEOUT Pq Vt struct timeval
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Sets or gets the
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.Dq Em read timeout
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parameter.
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The
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.Fa timeval
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.Vt timeval
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specifies the length of time to wait before timing
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out on a read request.
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This parameter is initialized to zero by
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.Xr open 2 ,
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indicating no timeout.
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.It Dv BIOCGSTATS ( struct bpf_stat )
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.It Dv BIOCGSTATS Pq Vt struct bpf_stat
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Returns the following structure of packet statistics:
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.Bd -literal -offset indent
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struct bpf_stat {
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@ -208,21 +215,23 @@ struct bpf_stat {
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.Ed
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.Pp
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The fields are:
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.Bl -tag -width bs_recv -offset indent
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.It Va bs_recv
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.Bl -tag -width Fa -offset indent
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.It Fa bs_recv
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the number of packets received by the descriptor since opened or reset
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(including any buffered since the last read call);
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.It Va bs_drop
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.Pq including any buffered since the last read call ;
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.It Fa bs_drop
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the number of packets which were accepted by the filter but dropped by the
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kernel because of buffer overflows
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(i.e., the application's reads aren't keeping up with the packet
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traffic); and
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.It Va bs_capt
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.Po
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i.e., the application's reads aren't keeping up with the packet traffic
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.Pc ;
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and
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.It Fa bs_capt
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the number of packets accepted by the filter.
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.El
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.It Dv BIOCIMMEDIATE ( u_int )
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.It Dv BIOCIMMEDIATE Pq Vt u_int
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Enables or disables
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.Dq immediate mode ,
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.Dq Em immediate mode ,
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based on the truth value of the argument.
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When immediate mode is enabled, reads return immediately upon packet
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reception.
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@ -232,11 +241,11 @@ This is useful for programs like
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.Xr rarpd 8 ,
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which must respond to messages in real time.
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The default for a new file is off.
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.Dv BIOCLOCK
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.It Dv BIOCLOCK Pq Dv NULL
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Set the locked flag on the bpf descriptor.
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This prevents the execution of ioctl commands which could change the
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underlying operating parameters of the device.
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.It Dv BIOCSETF ( struct bpf_program )
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.It Dv BIOCSETF Pq Vt struct bpf_program
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Sets the filter program used by the kernel to discard uninteresting
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packets.
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An array of instructions and its length are passed in using the following structure:
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@ -248,26 +257,26 @@ struct bpf_program {
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.Ed
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.Pp
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The filter program is pointed to by the
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.Va bf_insns
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.Fa bf_insns
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field while its length in units of
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.Sq struct bpf_insn
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.Vt struct bpf_insn
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is given by the
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.Va bf_len
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.Fa bf_len
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field.
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Also, the actions of
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.Dv BIOCFLUSH
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are performed.
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.Pp
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See section
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.Sy FILTER MACHINE
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.Sx FILTER MACHINE
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for an explanation of the filter language.
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.It Dv BIOCSETWF ( struct bpf_program )
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.It Dv BIOCSETWF Pq Vt struct bpf_program
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Sets the write filter program used by the kernel to control what type
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of packets can be written to the interface.
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See the
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.Dv BIOCSETF
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command for more information on the bpf filter program.
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.It Dv BIOCVERSION ( struct bpf_version )
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.It Dv BIOCVERSION Pq Vt struct bpf_version
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Returns the major and minor version numbers of the filter language currently
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recognized by the kernel.
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Before installing a filter, applications must check
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@ -289,16 +298,19 @@ and
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from
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.In net/bpf.h .
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An incompatible filter
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may result in undefined behavior (most likely, an error returned by
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may result in undefined behavior
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.Po
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most likely, an error returned by
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.Xr ioctl 2
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or haphazard packet matching).
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.It Dv BIOCSRSIG , BIOCGRSIG ( u_int )
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or haphazard packet matching
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.Pc .
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.It Dv BIOCSRSIG , BIOCGRSIG Pq Vt u_int
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Sets or gets the receive signal.
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This signal will be sent to the process or process group specified by
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.Dv FIOSETOWN .
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It defaults to
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.Dv SIGIO .
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.It Dv BIOCGHDRCMPLT , BIOCSHDRCMPLT ( u_int )
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.It Dv BIOCGHDRCMPLT , BIOCSHDRCMPLT Pq Vt u_int
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Sets or gets the status of the
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.Dq header complete
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flag.
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@ -307,7 +319,7 @@ automatically by the interface output routine.
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Set to one if the link level source address will be written,
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as provided, to the wire.
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This flag is initialized to zero by default.
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.It Dv BIOCGSEESENT , BIOCSSEESENT ( u_int )
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.It Dv BIOCGSEESENT , BIOCSSEESENT Pq Vt u_int
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These commands are obsolete but left for compatibility.
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Use
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.Dv BIOCSDIRECTION
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@ -319,7 +331,7 @@ interface should be returned by BPF.
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Set to zero to see only incoming packets on the interface.
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Set to one to see packets originating locally and remotely on the interface.
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This flag is initialized to one by default.
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.It Dv BIOCSDIRECTION , BIOCGDIRECTION Pq Li u_int
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.It Dv BIOCSDIRECTION , BIOCGDIRECTION Pq Vt u_int
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Set or get the setting determining whether incoming, outgoing, or all packets
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on the interface should be returned by BPF.
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Set to
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@ -334,7 +346,7 @@ to see only outgoing packets on the interface.
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This setting is initialized to
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.Dv BPF_D_INOUT
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by default.
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.It Dv BIOCFEEDBACK , BIOCSFEEDBACK , BIOCGFEEDBACK ( u_int )
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.It Dv BIOCFEEDBACK , BIOCSFEEDBACK , BIOCGFEEDBACK Pq Vt u_int
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Set (or get)
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.Dq packet feedback mode .
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This allows injected packets to be fed back as input to the interface when
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@ -352,19 +364,19 @@ This flag is initialized to zero by default.
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.El
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.Sh STANDARD IOCTLS
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.Nm
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now supports several standard
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.Xr ioctl 2 Ns 's
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supports several standard
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.Xr ioctl 2 Ap s
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which allow the user to do async and/or non-blocking I/O to an open
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.Nm bpf
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file descriptor.
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.Bl -tag -width indent -offset indent
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.It Dv FIONREAD ( int )
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.Bl -tag -width Dv
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.It Dv FIONREAD Pq Vt int
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Returns the number of bytes that are immediately available for reading.
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.It Dv FIONBIO ( int )
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.It Dv FIONBIO Pq Vt int
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Set or clear non-blocking I/O.
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If arg is non-zero, then doing a
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.Xr read 2
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when no data is available will return -1 and
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when no data is available will return \-1 and
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.Va errno
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will be set to
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.Er EAGAIN .
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@ -372,20 +384,22 @@ If arg is zero, non-blocking I/O is disabled.
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Note: setting this
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overrides the timeout set by
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.Dv BIOCSRTIMEOUT .
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.It Dv FIOASYNC ( int )
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.It Dv FIOASYNC Pq Vt int
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Enable or disable async I/O.
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When enabled (arg is non-zero), the process or process group specified by
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.Dv FIOSETOWN
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will start receiving SIGIO's when packets
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arrive.
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will start receiving
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.Dv SIGIO Ap s
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when packets arrive.
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Note that you must do an
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.Dv FIOSETOWN
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in order for this to take effect, as
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the system will not default this for you.
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The signal may be changed via
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.Dv BIOCSRSIG .
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.It Dv FIOSETOWN , FIOGETOWN ( int )
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Set or get the process or process group (if negative) that should receive SIGIO
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.It Dv FIOSETOWN , FIOGETOWN Pq Vt int
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Set or get the process or process group (if negative) that should receive
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.Dv SIGIO
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when packets are available.
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The signal may be changed using
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.Dv BIOCSRSIG
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@ -404,42 +418,44 @@ struct bpf_hdr {
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.Ed
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.Pp
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The fields, whose values are stored in host order, are:
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.Bl -tag -width bh_datalen -offset indent
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.It Va bh_tstamp
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.Bl -tag -width Fa -offset indent
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.It Fa bh_tstamp
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The time at which the packet was processed by the packet filter.
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This structure differs from the standard
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.Vt struct timeval
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in that both members are of type
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.Vt long .
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.It Va bh_caplen
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.It Fa bh_caplen
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The length of the captured portion of the packet.
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This is the minimum of
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the truncation amount specified by the filter and the length of the packet.
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.It Va bh_datalen
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.It Fa bh_datalen
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The length of the packet off the wire.
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This value is independent of the truncation amount specified by the filter.
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.It Va bh_hdrlen
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.It Fa bh_hdrlen
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The length of the BPF header, which may not be equal to
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.Em sizeof(struct bpf_hdr) .
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.Li sizeof(struct bpf_hdr) .
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.El
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.Pp
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The
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.Va bh_hdrlen
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.Fa bh_hdrlen
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field exists to account for
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padding between the header and the link level protocol.
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The purpose here is to guarantee proper alignment of the packet
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data structures, which is required on alignment sensitive
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architectures and improves performance on many other architectures.
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The packet filter ensures that the
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.Va bpf_hdr
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.Vt bpf_hdr
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and the
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.Em network layer
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header will be word aligned.
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Suitable precautions must be taken when accessing the link layer
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protocol fields on alignment restricted machines.
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(This isn't a problem on an Ethernet, since
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.Po
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This isn't a problem on an Ethernet, since
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the type field is a short falling on an even offset,
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and the addresses are probably accessed in a bytewise fashion).
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and the addresses are probably accessed in a bytewise fashion
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.Pc .
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.Pp
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Additionally, individual packets are padded so that each starts
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on a word boundary.
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@ -451,12 +467,15 @@ is defined in
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.In net/bpf.h
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to facilitate this process.
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It rounds up its argument
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to the nearest word aligned value (where a word is
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to the nearest word aligned value
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.Po
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where a word is
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.Dv BPF_ALIGNMENT
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bytes wide).
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bytes wide
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.Pc .
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.Pp
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For example, if
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.Sq Va p
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.Va p
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points to the start of a packet, this expression
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will advance it to the next packet:
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.Pp
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|
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@ -469,9 +488,10 @@ must itself be word aligned.
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.Xr malloc 3
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will always return an aligned buffer.
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.Sh FILTER MACHINE
|
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A filter program is an array of instructions, with all branches forwardly
|
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directed, terminated by a
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.Sy return
|
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A filter program is an array of instructions, with all branches
|
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.Em forwardly directed ,
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terminated by a
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.Em return
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instruction.
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Each instruction performs some action on the pseudo-machine state,
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which consists of an accumulator, index register, scratch memory store,
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|
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@ -488,42 +508,72 @@ struct bpf_insn {
|
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.Ed
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.Pp
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The
|
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.Va k
|
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.Fa k
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field is used in different ways by different instructions,
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and the
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.Va jt
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.Fa jt
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and
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.Va jf
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.Fa jf
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fields are used as offsets
|
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by the branch instructions.
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The opcodes are encoded in a semi-hierarchical fashion.
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There are eight classes of instructions: BPF_LD, BPF_LDX, BPF_ST, BPF_STX,
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BPF_ALU, BPF_JMP, BPF_RET, and BPF_MISC.
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There are eight classes of instructions:
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.Dv BPF_LD ,
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.Dv BPF_LDX ,
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.Dv BPF_ST ,
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.Dv BPF_STX ,
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.Dv BPF_ALU ,
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.Dv BPF_JMP ,
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.Dv BPF_RET ,
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and
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.Dv BPF_MISC .
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Various other mode and
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operator bits are or'd into the class to give the actual instructions.
|
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operator bits are
|
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.Em or Ap d
|
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into the class to give the actual instructions.
|
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The classes and modes are defined in
|
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.In net/bpf.h .
|
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.Pp
|
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Below are the semantics for each defined BPF instruction.
|
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We use the convention that A is the accumulator, X is the index register,
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P[] packet data, and M[] scratch memory store.
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P[i:n] gives the data at byte offset
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.Dq i
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We use the convention that
|
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.Ar A
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is the accumulator,
|
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.Ar X
|
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is the index register,
|
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.Ar P
|
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packet data, and
|
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.Ar M
|
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scratch memory store.
|
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.Sm off
|
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.Ar P Li \&[ Ar i Li \&: Ar n\^ Li \&]
|
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.Sm on
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gives the data at byte offset
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.Ar i
|
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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
|
||||
interpreted as a word
|
||||
.Ar ( n No = 4 ) ,
|
||||
unsigned halfword
|
||||
.Ar ( n No = 2 ) ,
|
||||
or unsigned byte
|
||||
.Ar ( n No = 1 ) .
|
||||
.Sm off
|
||||
.Ar M\^ Li \&[ Ar i\^ Li \&]
|
||||
.Sm on
|
||||
gives the
|
||||
.Ar i Ap 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.
|
||||
.Va k ,
|
||||
.Va jt ,
|
||||
The memory store is indexed from 0 to
|
||||
.Dv BPF_MEMWORDS Ns Li \&-1 .
|
||||
.Fa k ,
|
||||
.Fa jt ,
|
||||
and
|
||||
.Va jf
|
||||
.Fa jf
|
||||
are the corresponding fields in the
|
||||
instruction definition.
|
||||
.Dq len
|
||||
.Ar len
|
||||
refers to the length of the packet.
|
||||
.Bl -tag -width indent -offset indent
|
||||
.Bl -tag -width indent
|
||||
.It Sy BPF_LD
|
||||
These instructions copy a value into the accumulator.
|
||||
The type of the source operand is specified by an
|
||||
|
|
@ -683,7 +733,7 @@ array initializers:
|
|||
The following sysctls are available when
|
||||
.Nm
|
||||
is enabled:
|
||||
.Bl -tag -width "XnetXbpfXmaxbufsizeXX"
|
||||
.Bl -tag -width ".Li net.bpf.maxbufsize"
|
||||
.It Li net.bpf.maxbufsize
|
||||
Sets the maximum buffer size available for
|
||||
.Nm
|
||||
|
|
@ -707,12 +757,12 @@ utility.
|
|||
On architectures with
|
||||
.Xr bpfjit 4
|
||||
support, the additional sysctl is available:
|
||||
.Bl -tag -width "XnetXbpfXjitXX"
|
||||
.Bl -tag -width ".Li net.bpf.jit"
|
||||
.It Li net.bpf.jit
|
||||
Toggle
|
||||
.Sy Just-In-Time
|
||||
.Em just-in-time
|
||||
compilation of new filter programs.
|
||||
In order to enable Just-In-Time compilation,
|
||||
In order to enable just-in-time compilation,
|
||||
the bpfjit kernel module must be loaded.
|
||||
Changing a value of this sysctl doesn't affect
|
||||
existing filter programs.
|
||||
|
|
@ -804,9 +854,12 @@ The design was in collaboration with
|
|||
.An Van Jacobson ,
|
||||
also of Lawrence Berkeley Laboratory.
|
||||
.Sh BUGS
|
||||
The read buffer must be of a fixed size (returned by the
|
||||
The read buffer must be of a fixed size
|
||||
.Po
|
||||
returned by the
|
||||
.Dv BIOCGBLEN
|
||||
ioctl).
|
||||
ioctl
|
||||
.Pc .
|
||||
.Pp
|
||||
A file that does not request promiscuous mode may receive promiscuously
|
||||
received packets as a side effect of another file requesting this
|
||||
|
|
@ -815,16 +868,16 @@ 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 use a filter to reject foreign packets.
|
||||
.\" .Pp
|
||||
.\" Under SunOS, if a BPF application reads more than 2^31 bytes of
|
||||
.\" data, read will fail in
|
||||
.\" .Er EINVAL .
|
||||
.\" You can either fix the bug in SunOS,
|
||||
.\" or lseek to 0 when read fails for this reason.
|
||||
.Pp
|
||||
Under SunOS, if a BPF application reads more than 2^31 bytes of
|
||||
data, read will fail in
|
||||
.Er EINVAL .
|
||||
You can either fix the bug in SunOS,
|
||||
or lseek to 0 when read fails for this reason.
|
||||
.Pp
|
||||
.Dq Immediate mode
|
||||
.Dq Em Immediate mode
|
||||
and the
|
||||
.Dq read timeout
|
||||
.Dq Em read timeout
|
||||
are misguided features.
|
||||
This functionality can be emulated with non-blocking mode and
|
||||
.Xr select 2 .
|
||||
|
|
|
|||
Loading…
Reference in New Issue