Re: Let's do P4

[Jakub Kicinski <kubakici@wp.pl>]

On Sat, 29 Oct 2016 09:53:28 +0200, Jiri Pirko wrote:
> Hi all.
> 
> The network world is divided into 2 general types of hw:
> 1) network ASICs - network specific silicon, containing things like TCAM
>    These ASICs are suitable to be programmed by P4.
> 2) network processors - basically a general purpose CPUs
>    These processors are suitable to be programmed by eBPF.
> 
> I believe that by now, the most people came to a conclusion that it is
> very difficult to handle both types by either P4 or eBPF. And since
> eBPF is part of the kernel, I would like to introduce P4 into kernel
> as well. Here's a plan:
> 
> 1) Define P4 intermediate representation
>    I cannot imagine loading P4 program (c-like syntax text file) into
>    kernel as is. That means that as the first step, we need find some
>    intermediate representation. I can imagine someting in a form of AST,
>    call it "p4ast". I don't really know how to do this exactly though,
>    it's just an idea.
> 
>    In the end there would be a userspace precompiler for this:
>    $ makep4ast example.p4 example.ast

Maybe stating the obvious, but IMHO defining the IR is the hardest part.
eBPF *is* the IR, we can compile C, P4 or even JIT Lua to eBPF.  The
AST/IR for switch pipelines should allow for similar flexibility.
Looser coupling would also protect us from changes in spec of the high
level language.