netdev - Re: [PATCH 3/6] vsock: add netdev to vhost/virtio vsock

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Date:   Tue, 16 Aug 2022 11:07:17 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Bobby Eshleman <bobby.eshleman@...il.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Bobby Eshleman <bobbyeshleman@...il.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] vsock: add netdev to vhost/virtio vsock

On Tue, 16 Aug 2022 12:38:52 -0400 Michael S. Tsirkin wrote:
> On Mon, Aug 15, 2022 at 10:56:06AM -0700, Bobby Eshleman wrote:
> > In order to support usage of qdisc on vsock traffic, this commit
> > introduces a struct net_device to vhost and virtio vsock.
> > 
> > Two new devices are created, vhost-vsock for vhost and virtio-vsock
> > for virtio. The devices are attached to the respective transports.
> > 
> > To bypass the usage of the device, the user may "down" the associated
> > network interface using common tools. For example, "ip link set dev
> > virtio-vsock down" lets vsock bypass the net_device and qdisc entirely,
> > simply using the FIFO logic of the prior implementation.  
> 
> Ugh. That's quite a hack. Mark my words, at some point we will decide to
> have down mean "down".  Besides, multiple net devices with link up tend
> to confuse userspace. So might want to keep it down at all times
> even short term.

Agreed!

From a cursory look (and Documentation/ would be nice..) it feels
very wrong to me. Do you know of any uses of a netdev which would 
be semantically similar to what you're doing? Treating netdevs as
buildings blocks for arbitrary message passing solutions is something 
I dislike quite strongly.

Could you recommend where I can learn more about vsocks?