Re: [PATCH net-next v2 2/7] um: vector: honor virtio net hdr conversion failures

On Fri, 2026-10-16 at 05:43 -0400, Michael S. Tsirkin wrote:

quoted

quoted

quoted

quoted

-	virtio_net_hdr_to_skb(skb, vheader, virtio_legacy_is_little_endian());
+	if (virtio_net_hdr_to_skb(skb, vheader,
+			virtio_legacy_is_little_endian()) < 0)
+		return -1;
 	return 0;

Seems it'd be simpler to just

	return virtio_net_hdr_to_skb(...);

As far as I can tell, the function only returns -EINVAL or 0 (never a
positive value), and the caller only cares about negative (error) or
positive (no checksum needed), so that'd be equivalent?

johannes

if raw_verify_header can safely return any errno - i did not want to
audit it.

You already used an LLM and still didn't want to? ;-)

I checked briefly (by hand) and it seems fine, it's assigned to the
function pointer, which only has two callers on the _kern.c side.

johannes

                               header_check = vp->verify_header(
                                        mmsg_vector->msg_hdr.msg_iov->iov_base,
                                        skb,
                                        vp
                                );
                                if (header_check < 0) {
                                /* Overlay header failed to verify - discard.
                                 * We can actually keep this skb and reuse it,
                                 * but that will make the prep logic too
                                 * complex.
                                 */
                                        dev_kfree_skb_irq(skb);
                                        vp->estats.rx_encaps_errors++;
                                        (*skbuff_vector) = NULL;
                                        mmsg_vector++;
                                        skbuff_vector++;
                                        continue;
                                }
                                if (header_check > 0) {
                                        vp->estats.rx_csum_offload_good++;
                                        skb->ip_summed = CHECKSUM_UNNECESSARY;
                                }



so any negative is fine, but if we return 1 then it will force to CHECKSUM_UNNECESSARY
which I am not sure is what was intended?

Right, but virtio_net_hdr_to_skb() cannot return 1, only 0 on success
and -ERROR on failure?

johannes