netdev - Re: [RFC,POC] iptables/nftables to epbf/xdp via common intermediate layer

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Message-ID: <20180315202611.ucxpgeynlvpzuuqk@ast-mbp.dhcp.thefacebook.com>
Date:   Thu, 15 Mar 2018 13:26:12 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Edward Cree <ecree@...arflare.com>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        ast@...nel.org, pablo@...filter.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC,POC] iptables/nftables to epbf/xdp via common intermediate
 layer

On Thu, Mar 15, 2018 at 06:00:22PM +0100, Florian Westphal wrote:
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> > The way this IMR defined today looks pretty much like nft and
> > it feels a bit too low level than iptable conversion would need.
> 
> It wasn't so much about a specific IMR but to avoid code duplication
> between nft and iptables translators.
> 
> > I think it would be simpler to have user space only extensions
> > and opcodes added to bpf for the purpose of the translation.
> > Like there is no bpf instruction called 'load from IP header',
> > but we can make one. Just extend extended bpf with an instruction
> > like this and on the first pass do full conversion of nft
> > directly into this 'extended extended bpf'.
> 
> I don't want to duplicate any ebpf conversion (and optimisations)
> in the nft part.
> 
> If nft can be translated to this 'extended extended bpf' and
> this then generates bpf code from nft input all is good.

if possible it's great to avoid duplication, but it shouldn't be
such ultimate goal that it cripples iptable->bpf conversion
just to reuse nft->bpf bits.