netdev - Re: [RFC] virtio-net: share receive_*() and add_recvbuf

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Date:   Mon, 15 Jul 2019 17:16:09 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [RFC] virtio-net: share receive_*() and add_recvbuf_*() with
 virtio-vsock


>>>>>>>        struct sk_buff *virtskb_receive_small(struct virtskb *vs, ...);
>>>>>>>        struct sk_buff *virtskb_receive_big(struct virtskb *vs, ...);
>>>>>>>        struct sk_buff *virtskb_receive_mergeable(struct virtskb *vs, ...);
>>>>>>>
>>>>>>>        int virtskb_add_recvbuf_small(struct virtskb*vs, ...);
>>>>>>>        int virtskb_add_recvbuf_big(struct virtskb *vs, ...);
>>>>>>>        int virtskb_add_recvbuf_mergeable(struct virtskb *vs, ...);
>>>>>>>
>>>>>>> For the Guest->Host path it should be easier, so maybe I can add a
>>>>>>> "virtskb_send(struct virtskb *vs, struct sk_buff *skb)" with a part of the code
>>>>>>> of xmit_skb().
>>>>>> I may miss something, but I don't see any thing that prevents us from using
>>>>>> xmit_skb() directly.
>>>>>>
>>>>> Yes, but my initial idea was to make it more parametric and not related to the
>>>>> virtio_net_hdr, so the 'hdr_len' could be a parameter and the
>>>>> 'num_buffers' should be handled by the caller.
>>>>>
>>>>>>> Let me know if you have in mind better names or if I should put these function
>>>>>>> in another place.
>>>>>>>
>>>>>>> I would like to leave the control part completely separate, so, for example,
>>>>>>> the two drivers will negotiate the features independently and they will call
>>>>>>> the right virtskb_receive_*() function based on the negotiation.
>>>>>> If it's one the issue of negotiation, we can simply change the
>>>>>> virtnet_probe() to deal with different devices.
>>>>>>
>>>>>>
>>>>>>> I already started to work on it, but before to do more steps and send an RFC
>>>>>>> patch, I would like to hear your opinion.
>>>>>>> Do you think that makes sense?
>>>>>>> Do you see any issue or a better solution?
>>>>>> I still think we need to seek a way of adding some codes on virtio-net.c
>>>>>> directly if there's no huge different in the processing of TX/RX. That would
>>>>>> save us a lot time.
>>>>> After the reading of the buffers from the virtqueue I think the process
>>>>> is slightly different, because virtio-net will interface with the network
>>>>> stack, while virtio-vsock will interface with the vsock-core (socket).
>>>>> So the virtio-vsock implements the following:
>>>>> - control flow mechanism to avoid to loose packets, informing the peer
>>>>>     about the amount of memory available in the receive queue using some
>>>>>     fields in the virtio_vsock_hdr
>>>>> - de-multiplexing parsing the virtio_vsock_hdr and choosing the right
>>>>>     socket depending on the port
>>>>> - socket state handling
>>
>> I think it's just a branch, for ethernet, go for networking stack. otherwise
>> go for vsock core?
>>
> Yes, that should work.
>
> So, I should refactor the functions that can be called also from the vsock
> core, in order to remove "struct net_device *dev" parameter.
> Maybe creating some wrappers for the network stack.
>
> Otherwise I should create a fake net_device for vsock_core.
>
> What do you suggest?


I'm not quite sure I get the question. Can you just use the one that 
created by virtio_net?


Thanks