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

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Date:   Tue, 6 Mar 2018 17:24:48 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     Florian Westphal <fw@...len.de>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     <netdev@...r.kernel.org>, <ast@...nel.org>, <pablo@...filter.org>
Subject: Re: [RFC,POC] iptables/nftables to epbf/xdp via common intermediate
 layer

On 06/03/18 16:42, Florian Westphal wrote:
> I would also add 'highlevel' objects that are themselves translated into
> basic operations.  Most obvious example
> are 'fetch 4 bytes x bytes into transport header'.
>
> Frontend should not need to bother with ipv4 details, such as ip
> options.  Instead IMR should take care of this and generate the needed
> instructions to fetch iph->ihl and figure out the correct transport
> header offset.
Presumably then for this the IMR regs will cease to have any connection to
 BPF regs and will simply be (SSA?) r0, r1, ... as far as needed (not
 limited to 10 regs like BPF)?  Then register allocation all happens in
 the IMR->BPF conversion (even for things 64 bits or smaller).

I wonder how sophisticated we should be about register allocation; whether
 we should go the whole hog with graph-colouring algorithms or linear
 scan, or just do something naïve like an LRU.

Relatedly, should we spill values to the stack when we run out of
 registers, or should we just rely on being able to rematerialise them
 from parsing the packet again?

-Ed