netdev - Re: [PATCH net-next 0/3] support changing steering policies in tuntap

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Date:   Thu, 28 Sep 2017 12:09:05 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 0/3] support changing steering policies in tuntap

On Thu, Sep 28, 2017 at 3:23 AM, Jason Wang <jasowang@...hat.com> wrote:
>
>
> On 2017年09月28日 07:25, Willem de Bruijn wrote:
>>>>
>>>> In the future, both simple and sophisticated policy like RSS or other
>>>> guest
>>>> driven steering policies could be done on top.
>>>
>>> IMHO there should be a more practical example before adding all this
>>> indirection. And it would be nice to understand why this queue selection
>>> needs to be tun specific.
>>
>> I was thinking the same and this reminds me of the various strategies
>> implemented in packet fanout. tun_cpu_select_queue is analogous to
>> fanout_demux_cpu though it is tun-specific in that it requires
>> tun->numqueues.
>
>
> Right, the main idea is to introduce a way to change flow steering policy
> for tun. I think fanout policy could be implemented through the API
> introduced in this series. (Current flow caches based automatic steering
> method is tun specific).
>
>>
>> Fanout accrued various strategies until it gained an eBPF variant. Just
>> supporting BPF is probably sufficient here, too.
>
>
> Technically yes, but for tun, it also serve for virt. We probably still need
> some hard coded policy which could be changed by guest until we can accept
> an BPF program from guest I think?

When would a guest choose the policy? As long as this is under control
of a host user, possibly unprivileged, allowing BPF here is moot, as any
user can run socket filter BPF already. Programming from the guest is
indeed different. I don't fully understand that use case.