linux-kernel - Re: [PATCH net-next] tuntap: Fallback to automq on TUNSETSTEERINGEBPF prog negative return

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Date:   Wed, 25 Sep 2019 12:08:10 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Matt Cover <werekraken@...il.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, davem@...emloft.net,
        ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com,
        Eric Dumazet <edumazet@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Matthew Cover <matthew.cover@...ckpath.com>,
        mail@...urcelik.de, pabeni@...hat.com,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        wangli39@...du.com, lifei.shirley@...edance.com,
        tglx@...utronix.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next] tuntap: Fallback to automq on TUNSETSTEERINGEBPF
 prog negative return


On 2019/9/24 上午12:31, Matt Cover wrote:
>> I think it's better to safe to just drop the packet instead of trying to
>> workaround it.
>>
> This patch aside, dropping the packet here
> seems like the wrong choice. Loading a
> prog at this hookpoint "configures"
> steering. The action of configuring
> steering should not result in dropped
> packets.
>
> Suboptimal delivery is generally preferable
> to no delivery. Leaving the behavior as-is
> (i.e. relying on netdev_cap_txqueue()) or
> making any return which doesn't fit in a
> u16 simply use queue 0 would be highly
> preferable to dropping the packet.
>
>> Thanks


It leaves a choice for steering ebpf program to drop the packet that it 
can't classify. But consider we have already had socket filter, it 
probably not a big problem since we can drop packets there.

Thanks