Re: [dpdk-dev] [PATCH v8 10/10] app/testpmd:test VxLAN Tx checksum offload

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2014-11-11 05:29, Liu, Jijiang:
> From: Olivier MATZ
> > On 11/10/2014 07:03 AM, Liu, Jijiang wrote:
> > > > - if PKT_TX_VXLAN_CKSUM is not set (legacy use case), then the
> > > >    driver use l2_len and l3_len to offload inner IP/UDP/TCP checksums.
> > >
> > > If the flag is not set, and imply that it is not VXLAN packet,  and do
> > > TX checksum offload as regular packet.
> > >
> > > > - if PKT_TX_VXLAN_CKSUM is set, then the driver has to use
> > > >    inner_l{23}_len instead of l{23}_len for the same operation.
> > > 
> > > Your understanding is not fully correct.
> > > The l{23}_len is still used for TX checksum offload, please refer to
> > > i40e_txd_enable_checksum()  implementation.
> > 
> > This fields are part of public mbuf API. You cannot say to refer to i40e PMD code
> > to understand how to use it.
> > 
> > > > Adding PKT_TX_VXLAN_CKSUM changes the semantic of l2_len and l3_len.
> > > > To fix this, I suggest to remove the new fields inner_l{23}_len then
> > > > add outer_l{23}_len instead. Therefore, the semantic of l2_len and
> > > > l3_len would not change, and a driver would always use the same field for a
> > > > specific offload.
> > > 
> > > Oh...
> > 
> > Does it mean you agree?
> 
> I don't agree to change inner_l{23}_len the name.
> The reason is that using the "inner" word means incoming packet is tunneling packet or encapsulation packet.
> if we add "outer"{2,3}_len, which will cause confusion when processing non-tunneling packet.

Sorry Jijiang, maybe I don't understand what you are saying, but I think
you missed something. Let me explain the problem.

For PKT_TX_IP_CKSUM, we must set l{2,3}_len.
When PKT_TX_VXLAN_CKSUM is set, PKT_TX_IP_CKSUM is related to inner IP, right?
So we must set inner_l{2,3}_len.
It means that PKT_TX_IP_CKSUM requires different fields to be set, depending
of PKT_TX_VXLAN_CKSUM. That's what Olivier calls a semantic change.
It's not acceptable for an API.

PKT_TX_IP_CKSUM should always be related to l{2,3}_len.
When PKT_TX_VXLAN_CKSUM is set, we should add outer_l{2,3}_len.

Please, correct me if I'm wrong or fix the API.

Thanks
-- 
Thomas