.\" @(#) $Header: /tcpdump/master/libpcap/pcap_datalink.3pcap.in,v 1.1 2008-10-21 07:33:02 guy Exp $
.\"
.\" Copyright (c) 1994, 1996, 1997
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that: (1) source code distributions
.\" retain the above copyright notice and this paragraph in its entirety, (2)
.\" distributions including binary code include the above copyright notice and
.\" this paragraph in its entirety in the documentation or other materials
.\" provided with the distribution, and (3) all advertising materials mentioning
.\" features or use of this software display the following acknowledgement:
.\" ``This product includes software developed by the University of California,
.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
.\" the University nor the names of its contributors may be used to endorse
.\" or promote products derived from this software without specific prior
.\" written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.TH PCAP_DATALINK 3PCAP "22 August 2010"
.SH NAME
pcap_datalink \- get the link-layer header type
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.ft
.LP
.ft B
int pcap_datalink(pcap_t *p);
.ft
.fi
.SH DESCRIPTION
.B pcap_datalink()
returns the link-layer header type for the live capture or ``savefile''
specified by
.IR p .
.PP
It must not be called on a pcap descriptor created by
.B pcap_create()
that has not yet been activated by
.BR pcap_activate() .
.PP
.I http://www.tcpdump.org/linktypes.html
lists the values
.B pcap_datalink()
can return and describes the packet formats that
correspond to those values.
.PP
Do
.B NOT
assume that the packets for a given capture or ``savefile`` will have
any given link-layer header type, such as
.B DLT_EN10MB
for Ethernet.  For example, the "any" device on Linux will have a
link-layer header type of
.B DLT_LINUX_SLL
even if all devices on the system at the time the "any" device is opened
have some other data link type, such as
.B DLT_EN10MB
for Ethernet.
.SH RETURN VALUE
.B pcap_datalink()
returns the link-layer header type on success and
.B PCAP_ERROR_NOT_ACTIVATED
if called on a capture handle that has been created but not activated.
.SH SEE ALSO
pcap(3PCAP), pcap-linktype(@MAN_MISC_INFO@)