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

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Date:   Mon, 15 Jul 2019 12:42:20 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...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

On Mon, Jul 15, 2019 at 05:16:09PM +0800, Jason Wang wrote:
> 
> > > > > > > >        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?

Sure, sorry but I missed that it is allocated in the virtnet_probe()!

Thanks,
Stefano