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by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
pcap_datalink - get the link-layer header type
int pcap_datalink(pcap_t *p);
pcap_datalink() returns the link-layer header type for the live capture
or ``savefile'' specified by p.
It must not be called on a pcap descriptor created by pcap_create(3)
that has not yet been activated by pcap_activate(3).
https://www.tcpdump.org/linktypes.html lists the values pcap_datalink()
can return and describes the packet formats that correspond to those
Do NOT assume that the packets for a given capture or ``savefile`` will
have any given link-layer header type, such as DLT_EN10MB for Ethernet.
For example, the "any" device on Linux will have a link-layer header
type of 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
DLT_EN10MB for Ethernet.
pcap_datalink() returns the link-layer header type on success and
PCAP_ERROR_NOT_ACTIVATED if called on a capture handle that has been
created but not activated.
7 April 2014 PCAP_DATALINK(3)