From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon@6wind.com>
Subject: Re: [PATCH v3 6/8] driver/virtio:enqueue vhost TX offload
Date: Wed, 04 Nov 2015 12:17:40 +0100
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References: <1446634456-413-1-git-send-email-jijiang.liu@intel.com>
 <1446634456-413-7-git-send-email-jijiang.liu@intel.com>
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Cc: dev@dpdk.org, "Michael S. Tsirkin" <mst@redhat.com>
To: Jijiang Liu <jijiang.liu@intel.com>
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2015-11-04 18:54, Jijiang Liu:
> +       /* if vhost TX checksum offload is required */
> +       if (m->ol_flags & PKT_TX_IP_CKSUM) {
> +               hdr->csum_start = m->l2_len;
> +               hdr->csum_offset = offsetof(struct ipv4_hdr, hdr_checksum);
> +       } else if (m->ol_flags & PKT_TX_L4_MASK) {
> +               hdr->csum_start = m->l2_len + m->l3_len;
> +               switch (m->ol_flags & PKT_TX_L4_MASK) {
> +               case PKT_TX_TCP_CKSUM:
> +                       hdr->csum_offset = offsetof(struct tcp_hdr, cksum);
> +                       break;
> +               case PKT_TX_UDP_CKSUM:
> +                       hdr->csum_offset = offsetof(struct udp_hdr,
> +                                                       dgram_cksum);
> +                       break;
> +               case PKT_TX_SCTP_CKSUM:
> +                       hdr->csum_offset = offsetof(struct sctp_hdr, cksum);
> +                       break;
> +               default:
> +                       break;
> +               }

The header checksum to offload is deduced from csum_offset.
Your vhost implementation do some parsing to deduce it:

> +	parse_ethernet(m, &l4_proto, &l4_hdr);
> +	if (hdr->flags == VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> +		if ((hdr->csum_start == m->l2_len) &&
> +			(hdr->csum_offset == offsetof(struct ipv4_hdr,
> +						hdr_checksum)))
> +			m->ol_flags |= PKT_TX_IP_CKSUM;
> +		else if (hdr->csum_start == (m->l2_len + m->l3_len)) {
> +			switch (hdr->csum_offset) {
> +			case (offsetof(struct tcp_hdr, cksum)):
> +				if (l4_proto == IPPROTO_TCP)
> +					m->ol_flags |= PKT_TX_TCP_CKSUM;
> +				break;
> +			case (offsetof(struct udp_hdr, dgram_cksum)):
> +				if (l4_proto == IPPROTO_UDP)
> +					m->ol_flags |= PKT_TX_UDP_CKSUM;
> +				break;
> +			case (offsetof(struct sctp_hdr, cksum)):
> +				if (l4_proto == IPPROTO_SCTP)
> +					m->ol_flags |= PKT_TX_SCTP_CKSUM;
> +				break;
> +			default:
> +				break;
> +			}
> +		}

The kernel doesn't work this way.
Please could you check that your virtio implementation works with a
vanilla Linux with or without vhost?
Thanks