Re: [PATCH 5/8] xen/netfront: read response from backend only once

[Juergen Gross <jgross@xxxxxxxx>]

On 17.05.21 16:20, Jan Beulich wrote:
> On 13.05.2021 12:02, Juergen Gross wrote:
> > In order to avoid problems in case the backend is modifying a response
> > on the ring page while the frontend has already seen it, just read the
> > response into a local buffer in one go and then operate on that buffer
> > only.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> with one remark:
>
> > @@ -830,24 +830,22 @@ static int xennet_get_extras(struct netfront_queue *queue,
> >                         break;
> >                 }
> >   
> > -		extra = (struct xen_netif_extra_info *)
> > -                       RING_GET_RESPONSE(&queue->rx, ++cons);
> > +               RING_COPY_RESPONSE(&queue->rx, ++cons, &extra);
> >   
> > -		if (unlikely(!extra->type ||
> > -                            extra->type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
> > +               if (unlikely(!extra.type ||
> > +                            extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
> >                         if (net_ratelimit())
> >                                 dev_warn(dev, "Invalid extra type: %d\n",
> > -                                       extra->type);
> > +                                       extra.type);
> >                         err = -EINVAL;
> >                 } else {
> > -                       memcpy(&extras[extra->type - 1], extra,
> > -                              sizeof(*extra));
> > +                       memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
> Maybe take the opportunity and switch to (type safe) structure
> assignment?
Yes, good idea.


Juergen

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