Re: [PATCH v6 3/4] tcp_vu: Support multibuffer frames in tcp_vu_sock_recv()

[Jon Maloy <jmaloy@redhat.com>]

On 2026-04-16 12:16, Laurent Vivier wrote:
> Previously, tcp_vu_sock_recv() assumed a 1:1 mapping between virtqueue
> elements and iovecs (one iovec per element), enforced by an ASSERT.
> This prevented the use of virtqueue elements with multiple buffers
> (e.g. when mergeable rx buffers are not negotiated and headers are
> provided in a separate buffer).
> 

[...]

> -		if (dlen > len)
> -			dlen = len;
> -		len -= dlen;
> +		dlen = frame[i].size - hdrlen;
>   
>   		/* The IPv4 header checksum varies only with dlen */
>   		if (previous_dlen != dlen)
>   			check |= IP4_CSUM;
>   		previous_dlen = dlen;
>   
> -		tcp_vu_prepare(c, conn, iov, buf_cnt, dlen, &check, push);
> +		tcp_vu_prepare(c, conn, iov, iov_cnt, dlen, &check, push);
>   
> -		vu_pad(elem[head[i]].in_sg, buf_cnt, dlen + hdrlen);
> -		vu_flush(vdev, vq, &elem[head[i]], buf_cnt, dlen + hdrlen);
> +		vu_pad(&iov[frame[i].idx_iovec], frame[i].num_iovec,
> +		       dlen + hdrlen);

This doesn't look right.
iov is already &iov_vu[frame[i].idx_iovec], set a few lines further up 
this patch.
I suspect your intention is to access it the way you do in tcp_vu_prepare:
vu_pad(iov, iov_cnt, dlen + hdrlen);

/jon

>   
>   		if (*c->pcap) {
> -			pcap_iov(iov, buf_cnt, VNET_HLEN,
> +			pcap_iov(iov, iov_cnt, VNET_HLEN,
>   				 dlen + hdrlen - VNET_HLEN);
>   		}
> +		vu_flush(vdev, vq, &elem[frame[i].idx_element],
> +			 frame[i].num_element, dlen + hdrlen);
>   
>   		conn->seq_to_tap += dlen;
>   	}