On Fri, Nov 20, 2020 at 07:50:42PM +0100, Eugenio Pérez wrote:
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/virtio/vhost-backend.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> index 222bbcc62d..317f1f96fa 100644
> --- a/hw/virtio/vhost-backend.c
> +++ b/hw/virtio/vhost-backend.c
> @@ -201,6 +201,34 @@ static int vhost_kernel_get_vq_index(struct vhost_dev *dev, int idx)
>      return idx - dev->vq_index;
>  }
>  
> +static int vhost_kernel_set_vq_enable(struct vhost_dev *dev, unsigned idx,
> +                                      bool enable)
> +{
> +    struct vhost_vring_file file = {
> +        .index = idx,
> +    };
> +
> +    if (!enable) {
> +        file.fd = -1; /* Pass -1 to unbind from file. */
> +    } else {
> +        struct vhost_net *vn_dev = container_of(dev, struct vhost_net, dev);
> +        file.fd = vn_dev->backend;
> +    }
> +
> +    return vhost_kernel_net_set_backend(dev, &file);

This is vhost-net specific even though the function appears to be
generic. Is there a plan to extend this to all devices?

> +}
> +
> +static int vhost_kernel_set_vring_enable(struct vhost_dev *dev, int enable)
> +{
> +    int i;
> +
> +    for (i = 0; i < dev->nvqs; ++i) {
> +        vhost_kernel_set_vq_enable(dev, i, enable);
> +    }
> +
> +    return 0;
> +}

I suggest exposing the per-vq interface (vhost_kernel_set_vq_enable())
in VhostOps so it follows the ioctl interface.
vhost_kernel_set_vring_enable() can be moved to vhost.c can loop over
all vqs if callers find it convenient to loop over all vqs.