Re: Headroom

["Gianluca Varenni" <gianluca.varenni () cacetech com>]

----- Original Message ----- 
From: "Harley Stenzel" <hstenzel () gmail com>
To: <tcpdump-workers () lists tcpdump org>
Sent: Friday, October 06, 2006 10:46 AM
Subject: [tcpdump-workers] Headroom


> Greetings--
>
> Has the idea of headroom for libpcap-based stack applications been
> discussed before?  The idea is to have a known amount of empty/usable
> space in front of the buffer given to the application by the
> pcap_dispatch callback, pcap_next(), or pcap_next_ex().
>
> It looks like it'd be a ((pcap_t *)p)->headroom, which would be added
> to p->offset and p->bufsize for malloc.
>
> p->offset would still have to guarantee alignment for for the data,
> not for the beginning of the buffer.
>
> Headroom would have to be specified at pcap_open_live() or
> pcap_open_offline() time, so it could alter the pcap_t initialization
> logic. I suppose the best approach would be to make an additional
> variant of those functions, so the prototype changes don't ripple to
> other apps.  Possibly have it be an additional options structure,
> which may be null to get the current behavior.
>
> Any thoughts?

Uhm, what's the purpose of some amount of memory put in front of the  pcap_t 
structure?
Maybe I don't understand your proposal completely...

GV

> Thanks.
>
> --Harley
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