Re: [PATCH net-next] xen-netback: support dynamic unbind/bind

[Wei Liu]

On Mon, Dec 23, 2019 at 09:59:23AM +0000, Paul Durrant wrote:
[...] 
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index f15ba3de6195..0c8a02a1ead7 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -585,6 +585,7 @@ int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
>  	struct net_device *dev = vif->dev;
>  	void *addr;
>  	struct xen_netif_ctrl_sring *shared;
> +	RING_IDX rsp_prod, req_prod;
>  	int err;
>  
>  	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
> @@ -593,7 +594,14 @@ int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
>  		goto err;
>  
>  	shared = (struct xen_netif_ctrl_sring *)addr;
> -	BACK_RING_INIT(&vif->ctrl, shared, XEN_PAGE_SIZE);
> +	rsp_prod = READ_ONCE(shared->rsp_prod);
> +	req_prod = READ_ONCE(shared->req_prod);
> +
> +	BACK_RING_ATTACH(&vif->ctrl, shared, rsp_prod, XEN_PAGE_SIZE);
> +
> +	err = -EIO;
> +	if (req_prod - rsp_prod > RING_SIZE(&vif->ctrl))
> +		goto err_unmap;

I think it makes more sense to attach the ring after this check has been
done, but I can see you want to structure code like this to reuse the
unmap error path.

So:

Reviewed-by: Wei Liu <wei.liu@xxxxxxxxxx>

Nice work btw.