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Re: Remove hf_ variables
From: Bálint Réczey <balint () balintreczey hu>
Date: Tue, 6 Aug 2013 14:51:22 +0200

2013/7/30 Joerg Mayer <jmayer () loplof de>:
On Mon, Jul 29, 2013 at 10:42:02PM +0200, Jakub Zawadzki wrote:
On Mon, Jul 29, 2013 at 01:25:41PM -0700, Guy Harris wrote:

On Jul 29, 2013, at 1:12 PM, Jakub Zawadzki <darkjames-ws () darkjames pl> wrote:

Is anyone attached to hf_ variables? ;)

There's no real need of them, and we can just replace them with
header_field_info structure.

I.e., pass a pointer to the relevant structure, rather than an array index into an internal array that can supply 
that pointer?

Yes.

I'm not sure there's a compelling reason (other than the effort involved in converting code) to keep the variables.

Being devil's advocate I think there's no good reason to convert it.
Saving few CPU cycles by not doing:
 - load variable into memory
 - avoid PROTO_REGISTRAR_GET_NTH()

and some cycles on startup + max 2-3 MB less in binary doesn't seems like good deal
against converting 90% of dissectors codebase :)

If we don't loose functionality, I'd probably like to get rid of the extra
variables (both ett_ and hf_) as it makes coding a bit more convenient.
In the ett_ case: currently expansion is done similarly for all elements
using the same ett variable, how would that be done without these vars?

Can you give a sample diff how a dissector would need to be changed?
Also: What would be the migration plan: All at once or incremental?
If we plan making such big changes which require touching practically
every dissector, it would be nice to migrate dissection related global variables
into a context structure which would allow us to run several dissections on
several files in one binary.

Cheers,
Balint
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