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

On 17.05.21 16:20, Jan Beulich wrote:

On 13.05.2021 12:02, Juergen Gross wrote:

quoted

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@suse.com>

Reviewed-by: Jan Beulich <redacted>
with one remark:

quoted

@@ -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