Re: [RFC PATCH v3 02/10] net: Pad short frames to minimum size before send from SLiRP/TAP

[Jason Wang <jasowang@redhat.com>]

On 2021/3/9 4:35 下午, Bin Meng wrote:
> Hi Jason,
>
> On Tue, Mar 9, 2021 at 4:23 PM Jason Wang <jasowang@redhat.com> wrote:
>>
>> On 2021/3/8 6:22 下午, Peter Maydell wrote:
>>> On Mon, 8 Mar 2021 at 03:48, Jason Wang <jasowang@redhat.com> wrote:
>>>> Do we need to care about other type of networking backends? E.g socket.
>>>>
>>>> Or at least we should keep the padding logic if we can't audit all of
>>>> the backends.
>>> I think the key thing we need to do here is make a decision
>>> and be clear about what we're doing. There are three options
>>> I can see:
>>>
>>> (1) we say that the net API demands that backends pad
>>> packets they emit to the minimum ethernet frame length
>>> unless they specifically are intending to emit a short frame,
>>> and we fix any backends that don't comply (or equivalently,
>>> add support in the core code for a backend to mark itself
>>> as "I don't pad; please do it for me").
>>>
>>> (2) we say that the networking subsystem doesn't support
>>> short packets, and just have the common code always enforce
>>> padding short frames to the minimum length somewhere between
>>> when it receives a packet from a backend and passes it to
>>> a NIC model.
>>>
>>> (3) we say that it's the job of the NIC models to pad
>>> short frames as they see them coming in.
>>>
>>> I think (3) is pretty clearly the worst of these, since it
>>> requires every NIC model to handle it; it has no advantages
>>> over (2) that I can see. I don't have a strong take on whether
>>> we'd rather have (1) or (2): it's a tradeoff between whether
>>> we support modelling of short frames vs simplicity of code.
>>> I'd just like us to be clear about what point or points in
>>> the code have the responsibility for padding short frames.
>>
>> I'm not sure how much value we can gain from (1). So (2) looks better to me.
>>
>> Bin or Philippe, want to send a new version?
>>
> I think this series does what (2) asks for. Or am I missing anything?


It only did the padding for user/TAP.

Thanks


>
> Regards,
> Bin
>