Re: [PATCH v7] virtio-vsock: Add support for multi devices

On Fri, 13 Jun 2025 at 06:57, Xuewei Niu <[email protected]> wrote:
>
> > On Sat, Apr 12, 2025 at 10:39 PM Xuewei Niu <[email protected]> wrote:
> > >
> > > This patch brings a new feature, called "multi devices", to the virtio
> > > vsock. It introduces a "VIRTIO_VSOCK_F_MULTI_DEVICES" feature bit, and a
> > > "device_order" field to the config for the virtio vsock.
> > >
> > > == Motivition ==
> > >
> > > Vsock is a lightweight and widely used data exchange mechanism between host
> > > and guest. Currently, the virtio-vsock only supports one device, resulting
> > > in the inability to enable more than one backend.
> >
> > I wonder which part of the spec forbids more than one device.
>
> No. The spec, however, is designed for a single device, and lacks some
> specifications for multiple devices.
>
> For example, we should have a mechanism to select a device from all to
> communicate with a peer.
>
> This patch introduces a new feature bit "VIRTIO_VSOCK_F_MULTI_DEVICES", and
> involves some modifications to the config space, device & driver norms.

Maybe we should think a better name to avoid confusion, like "F_DEVICE_ORDER".
I'm not good at name, so if others are better suggestion, they are welcome.

>
> > > For instance, two devices
> > > are required: one to transfer data to the VMM via virtio-vsock, and another
> > > to a user process via vhost-user-vsock.
> > >
> > > Apart from that, a side gain is that theoretically the performance might be
> > > improved since each device has its own queue. But it varies depending on
> > > the implementation.
> >
> > It could implement multiqueue anyhow.
> >
> > Thanks
>
> Yes, indeed. As we discussed before, I marked this as a side gain. And
> @Stefano said that the community has a plan to implement multiqueue for
> vsock.

I'm not sure there is a plan, but yeah, we should do it some day.
As I mention in the previous email, I'd remove any reference to performance.

I'd just talk about a mechanism to select a default out device, when
the source socket is not bound to any address, like a default gateway.

Thanks,
Stefano

> The foundational goal of this patch is to enable vsock to support
> multiple backends.
>
> Thanks,
> Xuewei
>