Re: function of dissector_try_uint()

[Pascal Quantin <pascal.quantin () gmail com>]

Hi Vishnu,

2015-02-16 14:55 GMT+01:00 Vishnu Bhatt <vishnu.bhatt () aricent com>:

>  Hi,
>
>
>
> I have a dissector code (atmii) and I am having problem in understanding
> the following two lines of code:
>
>
>
> In proto_register_atmii()
>
>
>
> aal_dissector_table = register_dissector_table("atmii.aal2_payload", "AAL
> payload type", FT_UINT8, BASE_DEC);

This create a dissector table (with a guint8 as identifier) that can be
used by other dissectors so as to register themselves as the dissector to
be called for a given payload type value, using something like:
dissector_add_uint("atmii.aal2_payload", my_payload_type_value,
my_dissector_handle);


> and then in dissect_atmii()
>
>
>
> if (!dissector_try_port(aal_dissector_table, payload_type, next_tvb,
> pinfo, tree)) {

I guess this is a typo and you meant dissector_try_uint, right?

proto_tree_add_item(atmii_tree,hf_atmii_aal2_payload, tvb,
> ATM_HEADER_LENGTH, -1, FALSE);
>
> }
>
>
>
>
>
> What does these two lines of code do in general as I’ve seen them in other
> protocols as well?

As indicated in proto.h:
/* Look for a given value in a given uint dissector table and, if found,
   call the dissector with the arguments supplied, and return the number
   of bytes consumed, otherwise return 0. */
WS_DLL_PUBLIC int dissector_try_uint(dissector_table_t sub_dissectors,
    const guint32 uint_val, tvbuff_t *tvb, packet_info *pinfo, proto_tree
*tree);

So with those 2 lines of code, your dissector tries to find a matching sub
dissector for the payload using the payload type as parameter. If no
matching dissector is found (reutnr value is 0), then it displays the
payload as a byte field probably (hf_atmii_aal2_payload).

Regards,
Pascal.

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