Wireshark-dev: Re: [Wireshark-dev] allocator->in_scope

From: Paul Offord <Paul.Offord@xxxxxxxxxxxx>
Date: Sun, 25 Mar 2018 18:35:08 +0000
Thanks for the advice (and note from Evan).

I haven't even begun to consider things like capinfos, mergecap, tshark, etc.  I guess now is the time to think about these things.

So just to clarify things here:

I have real dissector code that builds a protocol tree and so I guess this falls under libwireshark.  However, I also have two block read functions that are registered like this:

    register_pcapng_block_type_handler((guint)BLOCK_TYPE_TDB, tdb_read_block, NULL);
    register_pcapng_block_type_handler((guint)BLOCK_TYPE_TRB, trb_read_block, NULL);

Are my block read functions part of libwiretap?

I'm just wondering if I should split the code that reads the new blocks and the code that does the dissection.  It's not going to be easy.

-----Original Message-----
From: Wireshark-dev <wireshark-dev-bounces@xxxxxxxxxxxxx> On Behalf Of Guy Harris
Sent: 25 March 2018 19:11
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] allocator->in_scope

On Mar 25, 2018, at 10:39 AM, Paul Offord <Paul.Offord@xxxxxxxxxxxx> wrote:

> Even bigger aha.  Although I only have one new block in the pcapng file, when I open the file via the file explorer dialogue, my block reader is called twice; once to allow WS to enrich the dialogue box (I think) and a second time to read the block before dissection.  I never noticed this before, and this probably explains a few weird problems I have been grappling with.

What happens if you run the capinfos program on your file?

If your block reader is called in that case, then it cannot use the wmem allocators, as 1) the wmem routines are part of libwireshark and 2) capinfos doesn't use libwireshark.  The code to put the summary in the dialog box is similar to the capinfos call, in that it doesn't do any dissection, it just gets what statistics can be gathered without looking at the contents of any of the records, just the metadata at which libwiretap looks.

Your block *dissector* can use the wmem routines, as dissectors are part of libwireshark or are plugins that "belong to" libwireshark; code that is part of libwiretap or that is a plugin that "belongs to" libwiretap, however, cannot use the wmem routines.
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