Date:   Thu, 14 Nov 2019 19:11:36 +0900
From:   Toshiaki Makita <toshiaki.makita1@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Pravin B Shelar <pshelar@....org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        William Tu <u9012063@...il.com>,
        Stanislav Fomichev <sdf@...ichev.me>
Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP

On 2019/11/13 1:53, Toke Høiland-Jørgensen wrote:
> Toshiaki Makita <toshiaki.makita1@...il.com> writes:
>>
>> Hi Toke,
>>
>> Sorry for the delay.
>>
>> On 2019/10/31 21:12, Toke Høiland-Jørgensen wrote:
>>> Toshiaki Makita <toshiaki.makita1@...il.com> writes:
>>>
>>>> On 2019/10/28 0:21, Toke Høiland-Jørgensen wrote:
>>>>> Toshiaki Makita <toshiaki.makita1@...il.com> writes:
>>>>>>> Yeah, you are right that it's something we're thinking about. I'm not
>>>>>>> sure we'll actually have the bandwidth to implement a complete solution
>>>>>>> ourselves, but we are very much interested in helping others do this,
>>>>>>> including smoothing out any rough edges (or adding missing features) in
>>>>>>> the core XDP feature set that is needed to achieve this :)
>>>>>>
>>>>>> I'm very interested in general usability solutions.
>>>>>> I'd appreciate if you could join the discussion.
>>>>>>
>>>>>> Here the basic idea of my approach is to reuse HW-offload infrastructure
>>>>>> in kernel.
>>>>>> Typical networking features in kernel have offload mechanism (TC flower,
>>>>>> nftables, bridge, routing, and so on).
>>>>>> In general these are what users want to accelerate, so easy XDP use also
>>>>>> should support these features IMO. With this idea, reusing existing
>>>>>> HW-offload mechanism is a natural way to me. OVS uses TC to offload
>>>>>> flows, then use TC for XDP as well...
>>>>>
>>>>> I agree that XDP should be able to accelerate existing kernel
>>>>> functionality. However, this does not necessarily mean that the kernel
>>>>> has to generate an XDP program and install it, like your patch does.
>>>>> Rather, what we should be doing is exposing the functionality through
>>>>> helpers so XDP can hook into the data structures already present in the
>>>>> kernel and make decisions based on what is contained there. We already
>>>>> have that for routing; L2 bridging, and some kind of connection
>>>>> tracking, are obvious contenders for similar additions.
>>>>
>>>> Thanks, adding helpers itself should be good, but how does this let users
>>>> start using XDP without having them write their own BPF code?
>>>
>>> It wouldn't in itself. But it would make it possible to write XDP
>>> programs that could provide the same functionality; people would then
>>> need to run those programs to actually opt-in to this.
>>>
>>> For some cases this would be a simple "on/off switch", e.g.,
>>> "xdp-route-accel --load <dev>", which would install an XDP program that
>>> uses the regular kernel routing table (and the same with bridging). We
>>> are planning to collect such utilities in the xdp-tools repo - I am
>>> currently working on a simple packet filter:
>>> https://github.com/xdp-project/xdp-tools/tree/xdp-filter
>>
>> Let me confirm how this tool adds filter rules.
>> Is this adding another commandline tool for firewall?
>>
>> If so, that is different from my goal.
>> Introducing another commandline tool will require people to learn
>> more.
>>
>> My proposal is to reuse kernel interface to minimize such need for
>> learning.
> 
> I wasn't proposing that this particular tool should be a replacement for
> the kernel packet filter; it's deliberately fairly limited in
> functionality. My point was that we could create other such tools for
> specific use cases which could be more or less drop-in (similar to how
> nftables has a command line tool that is compatible with the iptables
> syntax).
> 
> I'm all for exposing more of the existing kernel capabilities to XDP.
> However, I think it's the wrong approach to do this by reimplementing
> the functionality in eBPF program and replicating the state in maps;
> instead, it's better to refactor the existing kernel functionality to it
> can be called directly from an eBPF helper function. And then ship a
> tool as part of xdp-tools that installs an XDP program to make use of
> these helpers to accelerate the functionality.
> 
> Take your example of TC rules: You were proposing a flow like this:
> 
> Userspace TC rule -> kernel rule table -> eBPF map -> generated XDP
> program
> 
> Whereas what I mean is that we could do this instead:
> 
> Userspace TC rule -> kernel rule table
> 
> and separately
> 
> XDP program -> bpf helper -> lookup in kernel rule table

Thanks, now I see what you mean.
You expect an XDP program like this, right?

int xdp_tc(struct xdp_md *ctx)
{
	int act = bpf_xdp_tc_filter(ctx);
	return act;
}

But doesn't this way lose a chance to reduce/minimize the program
to only use necessary features for this device?

Toshiaki Makita

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