Wireshark · Ethereal-dev: [Ethereal-dev] protocol handoff still confusing / README.developer out of date

[Ulf Lamping <ulf.lamping@xxxxxx>]

Hi List!

I've looked at the README.developer file to understand, how to call a 
subdissector from another one.

Some of the documentation on this topic seems to be out of date, "1.8 
Calling Other Dissector" gives an example from packet-ipx.c,
but that does no longer reflect the current implementation in this file.

As it also is hard to understand how things have to be done, I would 
like to correct/update/enhance the docs on this topic.


Could someone correct me on the following understanding:

In the upper layer dissector, the proto_reg_handoff_xy() function has to 
register the upper dissector at the lower one. This is done by first 
create a dissector_handle_t using create_dissector_handle() and then do 
a dissector_add() to a specific lower layer protocol field (typically an 
identifier of the upper layer protocol). Except from the 
README.developer skeleton code:

void
proto_reg_handoff_PROTOABBREV(void)
{
   dissector_handle_t PROTOABBREV_handle;

   PROTOABBREV_handle = create_dissector_handle(dissect_PROTOABBREV,
       proto_PROTOABBREV);
   dissector_add("PARENT_SUBFIELD", ID_VALUE, PROTOABBREV_handle);
}


In the lower layer code, the dissector will create a new tvb using 
tvb_new_subset(), and then call the upper layer dissector using 
call_dissector()


The only thing still missing in my understanding is the data_handle in 
the call to call_dissector(). At various places I've found:

data_handle = find_dissector("data");

but what's the use of this "data"?

Regards, ULFL