[dpdk-dev] [PATCH v3 6/8] driver/virtio:enqueue vhost TX offload

[Liu, Jijiang]

Hi Thomas,

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com]
> Sent: Wednesday, November 4, 2015 7:18 PM
> To: Liu, Jijiang
> Cc: dev at dpdk.org; Michael S. Tsirkin
> Subject: Re: [dpdk-dev] [PATCH v3 6/8] driver/virtio:enqueue vhost TX
> offload
> 
> 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:
> 
 The ol_flag is set in application, we have to fill 'csum_start' and  'csum_offset' based on these offload flags. 
As long as the 'csum_start' and  'csum_offset'  fileds are set correctly, and it can work well with a vanilla linux with vhost.

But in DPDK vhost lib, we need to parse the 'csum_start' and  'csum_offset' filed to get the which offload flags should be set, and the l2_len, l3_len and l3_len also should be filled.

So I think it is necessary to do this in both side.
We can continue discuss this if you have further comments. Thanks

--Jijiang Liu