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Note that captures on the "any" device won't be done in promiscuous

mode, regardless of the value of "promisc".
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1 parent ea57200 commit 8a891e0b697c191260aba84324bdd42f2378e71d @yuguy yuguy committed Jan 18, 2001
Showing with 77 additions and 45 deletions.
  1. +77 −45 pcap.3
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122 pcap.3
@@ -1,4 +1,4 @@
-.\" @(#) $Header: /tcpdump/master/libpcap/Attic/pcap.3,v 1.14 2000-12-12 09:31:45 guy Exp $
+.\" @(#) $Header: /tcpdump/master/libpcap/Attic/pcap.3,v 1.17.2.1 2001-01-18 04:42:11 guy Exp $
.\"
.\" Copyright (c) 1994, 1996, 1997
.\" The Regents of the University of California. All rights reserved.
@@ -19,7 +19,7 @@
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
-.TH PCAP 3 "24 July 2000"
+.TH PCAP 3 "3 January 2001"
.SH NAME
pcap \- Packet Capture library
.SH SYNOPSIS
@@ -122,9 +122,18 @@ specifies the maximum number of bytes to capture.
.I promisc
specifies if the interface is to be put into promiscuous mode.
(Note that even if this parameter is false, the interface
-could well be in promiscuous mode for some other reason.)
+could well be in promiscuous mode for some other reason.) For now, this
+doesn't work on the "any" device; if an argument of "any" or NULL is
+supplied, the
+.I promisc
+flag is ignored.
.I to_ms
-specifies the read timeout in milliseconds.
+specifies the read timeout in milliseconds. The read timeout is used to
+arrange that the read not necessarily return immediately when a packet
+is seen, but that it wait for some amount of time to allow more packets
+to arrive and to read multiple packets from the OS kernel in one
+operation. Not all platforms support a read timeout; on platforms that
+don't, the read timeout is ignored.
.I ebuf
is used to return error text and is only set when
.B pcap_open_live()
@@ -196,21 +205,22 @@ and
are
.I bpf_u_int32
pointers.
-A return of -1 indicates an error in which case
+A return of \-1 indicates an error in which case
.I errbuf
is filled in with an appropriate error message.
.PP
.B pcap_dispatch()
is used to collect and process packets.
.I cnt
-specifies the maximum number of packets to process before returning. A
+specifies the maximum number of packets to process before returning.
+This is not a minimum number; when reading a live capture, only one
+bufferful of packets is read at a time, so fewer than
.I cnt
-of -1 processes all the packets received in one buffer. A
+packets may be processed. A
.I cnt
-of 0 processes all packets until an error occurs,
-.B EOF
-is reached, or the read times out (when doing live reads and a non-zero
-read timeout is specified).
+of \-1 processes all the packets received in one buffer when reading a
+live capture, or all the packets in the file when reading a
+``savefile''.
.I callback
specifies a routine to be called with three arguments:
a
@@ -222,21 +232,69 @@ a pointer to the
struct (which precede the actual network headers and data),
and a
.I u_char
-pointer to the packet data. The number of packets read is returned.
-Zero is returned when
-.B EOF
-is reached in a ``savefile.'' A return of -1 indicates
+pointer to the packet data.
+.PP
+The number of packets read is returned.
+0 is returned if no packets were read from a live capture (if, for
+example, they were discarded because they didn't pass the packet filter,
+or if, on platforms that support a read timeout that starts before any
+packets arrive, the timeout expires before any packets arrive, or if the
+file descriptor for the capture device is in non-blocking mode and no
+packets were available to be read) or if no more packets are available
+in a ``savefile.'' A return of \-1 indicates
an error in which case
.B pcap_perror()
or
.B pcap_geterr()
may be used to display the error text.
.PP
+.BR NOTE :
+when reading a live capture,
+.B pcap_dispatch()
+will not necessarily return when the read times out; on some platforms,
+the read timeout isn't supported, and, on other platforms, the timer
+doesn't start until at least one packet arrives. This means that the
+read timeout should
+.B NOT
+be used in, for example, an interactive application, to allow the packet
+capture loop to ``poll'' for user input periodically, as there's no
+guarantee that
+.B pcap_dispatch()
+will return after the timeout expires.
+.PP
+.B pcap_loop()
+is similar to
+.B pcap_dispatch()
+except it keeps reading packets until
+.I cnt
+packets are processed or an error occurs.
+It does
+.B not
+return when live read timeouts occur.
+Rather, specifying a non-zero read timeout to
+.B pcap_open_live()
+and then calling
+.B pcap_dispatch()
+allows the reception and processing of any packets that arrive when the
+timeout occurs.
+A negative
+.I cnt
+causes
+.B pcap_loop()
+to loop forever (or at least until an error occurs).
+.PP
+.B pcap_next()
+returns a
+.I u_char
+pointer to the next packet.
+.PP
.B pcap_dump()
outputs a packet to the ``savefile'' opened with
.BR pcap_dump_open() .
Note that its calling arguments are suitable for use with
-.BR pcap_dispatch() .
+.B pcap_dispatch()
+or
+.BR pcap_loop() .
.PP
.B pcap_compile()
is used to compile the string
@@ -251,7 +309,7 @@ struct and is filled in by
controls whether optimization on the resulting code is performed.
.I netmask
specifies the netmask of the local net.
-A return of -1 indicates an error in which case
+A return of \-1 indicates an error in which case
.BR pcap_geterr()
may be used to display the error text.
.PP
@@ -263,7 +321,7 @@ snaplen and linktype explicitly. It is intended to be used for
compiling filters for direct BPF usage, without necessarily having
called
.BR pcap_open() .
-A return of -1 indicates an error; the error text is unavailable.
+A return of \-1 indicates an error; the error text is unavailable.
.RB ( pcap_compile_nopcap()
is a wrapper around
.BR pcap_open_dead() ,
@@ -297,32 +355,6 @@ when that BPF program is no longer needed, for example after it
has been made the filter program for a pcap structure by a call to
.BR pcap_setfilter() .
.PP
-.B pcap_loop()
-is similar to
-.B pcap_dispatch()
-except it keeps reading packets until
-.I cnt
-packets are processed or an error occurs.
-It does
-.B not
-return when live read timeouts occur.
-Rather, specifying a non-zero read timeout to
-.B pcap_open_live()
-and then calling
-.B pcap_dispatch()
-allows the reception and processing of any packets that arrive when the
-timeout occurs.
-A negative
-.I cnt
-causes
-.B pcap_loop()
-to loop forever (or at least until an error occurs).
-.PP
-.B pcap_next()
-returns a
-.I u_char
-pointer to the next packet.
-.PP
.B pcap_datalink()
returns the link layer type, e.g.
.BR DLT_EN10MB .
@@ -352,7 +384,7 @@ returns 0 and fills in a
.B pcap_stat
struct. The values represent packet statistics from the start of the
run to the time of the call. If there is an error or the under lying
-packet capture doesn't support packet statistics, -1 is returned and
+packet capture doesn't support packet statistics, \-1 is returned and
the error text can be obtained with
.B pcap_perror()
or

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