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Subject: Re: [RFC PATCH net-next V2 0/6] XDP rx handler
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     David Ahern <dsahern@gmail.com>,
        Jesper Dangaard Brouer <jbrouer@redhat.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        ast@kernel.org, daniel@iogearbox.net, mst@redhat.com
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <4e5c81ee-56ae-1d70-273e-c551ad6c932b@redhat.com>
Date:   Thu, 16 Aug 2018 12:24:07 +0800
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On 2018年08月16日 12:05, Alexei Starovoitov wrote:
> On Thu, Aug 16, 2018 at 11:34:20AM +0800, Jason Wang wrote:
>>> Nothing about the topology is hard coded. The idea is to mimic a
>>> hardware pipeline and acknowledging that a port device can have an
>>> arbitrary layers stacked on it - multiple vlan devices, bonds, macvlans, etc
>> I may miss something but BPF forbids loop. Without a loop how can we make
>> sure all stacked devices is enumerated correctly without knowing the
>> topology in advance?
> not following. why do you need a loop to implement macvlan as an xdp prog?
> if loop is needed, such algorithm is not going to scale whether
> it's implemented as bpf program or as in-kernel c code.

David said the port can have arbitrary layers stacked on it. So if we 
try to enumerate them before making forwarding decisions purely by BPF 
program, it looks to me a loop is needed here.

Thanks