Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC PATCH net-next V2 0/6] XDP rx handler
To:     Jason Wang <jasowang@redhat.com>,
        Jesper Dangaard Brouer <jbrouer@redhat.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        ast@kernel.org, daniel@iogearbox.net, mst@redhat.com
References: <1534130250-5302-1-git-send-email-jasowang@redhat.com>
 <20180814003253.fkgl6lyklc7fclvq@ast-mbp>
 <5de3d14f-f21a-c806-51f4-b5efd7d809b7@redhat.com>
 <20180814121734.105769fa@redhat.com>
 <03ab3b18-9b13-8169-7e68-ada307694bc1@redhat.com>
 <08bf7aec-078a-612d-833f-5b3d09a289d0@gmail.com>
 <aa9cf883-7822-70a7-5ab5-c873b69c2098@redhat.com>
 <f4c0346d-6665-5312-0310-ffbda505b7ec@gmail.com>
 <2792239a-ed3b-d66e-0c1c-e99455311eff@redhat.com>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <ae0e09a1-a20a-a2fc-36a0-82e109216bf4@gmail.com>
Date:   Fri, 17 Aug 2018 15:15:01 -0600
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0)
 Gecko/20100101 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <2792239a-ed3b-d66e-0c1c-e99455311eff@redhat.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 8/15/18 9:34 PM, Jason Wang wrote:
> 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?

netdev_for_each_upper_dev_rcu

BPF helpers allow programs to do lookups in kernel tables, in this case
the ability to find an upper device that would receive the packet.