pcap FCS length and LT_FCS_DATALINK_EXT()

[Stephen Donnelly <Stephen.Donnelly () emulex com>]

Hi Guy,

In 2007 in libpcap afbb1ce7 you committed some code (possibly from Florent Drouin) adding the LT_FCS_DATALINK_EXT 
mechanism to record whether the capture includes information about captured FCS length, and if so what length it is.

I believe that currently only the DAG capture code supports this, and as implemented the LT_FCS_LENGTH is in units of 
16-bits, e.g. 16-bit FCS returns 1, and 32-bit FCS returns 2?

I don't think Wireshark's pcap wiretap code currently uses this mechanism to check for FCS length, does it make sense 
to add it?

If it is supported in Wireshark, it might be more widely implemented. It seems to solve a genuine problem, and avoids 
the proliferation of DLTs for WITH and WITHOUT FCS.

Regards,
Stephen.

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