Re: [PATCH next v3] iptables: add xt_bpf match

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On Tue, 22 Jan 2013, Florian Westphal wrote:

> Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote:
> > On Fri, Jan 18, 2013 at 11:48:34AM -0500, Willem de Bruijn wrote:
> > [...]
> > > To compile code right now, the little bpf compiler that I emailed
> > > before can be downloaded from
> > > http://code.google.com/p/kernel/downloads/detail?name=bpf2decimal.c
> > > 
> > > I don't think that a compiler has to be shipped with iptables itself,
> > > let alone make iptables link against libraries. That said,  it is not
> > > impossible to detect pcap.h in configure.ac and optionally enable a
> > > "-m bpf --string" mode that calls pcap_compile_nopcap from within
> > > libxt_bpf, so let me know if you would like me to code that up. I can
> > > also try to send a patch to tcpdump that extends compilation (`-ddd -y
> > > <type>`) to arbitrary link layer types.
> > 
> > We have to decide if:
> > 
> > a) we add a new hard library dependency to iptables (libpcap) for just
> > for one single module, that is, the libxt_bpf depends on libpcap.
> > 
> > or
> > 
> > b) provide a separate utility to generate the BPF filter in text-based
> > format from some utility that accepts tcpdump-like syntax. The utility
> > can be distributed in the utils directory and it would not be
> > mandatory to compile it if libpcap is not present.
> > 
> > I'd like to hear pro and cons arguments from others on this.
> 
> a) is arguably more user friendly, however, I don't think we can
>    retain the 'text representation' for iptables-save so users
>    would still be confronted with the compiled data at some point
>    (i.e., they need to write down the original expression anyway to
>     figure out what the rule they added 6 months back actually does...)
> 
> I would go with b) for now; we can always move to a) later on, but not
> the other way around (would kill backwards compatibility).

Yes, let's go with b). (But from packaging point of view 
utils/bpf2decimal.c depending on libpcap is not much different from 
extensions/libxt_bpf.c depending on libpcap.)

Best regards,
Jozsef
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