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Date: Mon, 01 Dec 2014 10:52:03 +0100
From: Olivier MATZ <olivier.matz@6wind.com>
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To: "Liu, Jijiang" <jijiang.liu@intel.com>, 
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Subject: Re: [dpdk-dev] [PATCH 1/3] mbuf:add two TX offload flags and change
 three fields
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Hi Jijiang,

On 12/01/2014 03:30 AM, Liu, Jijiang wrote:
>> After another thought, I think that the way you proposed is a better one.
>> I gives us more flexibility:
>> let's say for now we'll keep both l2_len and outer_l2_len as 7 bit fields, and upper
>> layer would have to:
>> mb->l2_len =  eth_hdr_in + vxlan_hdr;
> 
> A question, how to fill the mb->l2_len  for IP in IP, IP in GRE tunneling packet that is no inner L2 header?
> What  is the rule?
> Or you think it should be mb->l2_len =  0 + l4_tun_len;  ??

We could have the following rule:
- the l2_len starts after the end of outer_l2_len + outer_l3_len (if
  they are not 0)
- l2_len is the length of all headers up to the first ip or ipv6
  header

Examples:

Ether/IP/UDP/xxx
  m->outer_l2_len = 0
  m->outer_l3_len = 0
  m->l2_len = sizeof(ether)
  m->l3_len = sizeof(ip)
  m->l4_len = sizeof(udp)

Ether/IP/IP/UDP/xxx
  m->outer_l2_len = sizeof(ether)
  m->outer_l3_len = sizeof(ip)
  m->l2_len = 0
  m->l3_len = sizeof(ip)
  m->l4_len = sizeof(udp)

Ether/IP/GRE/IP/UDP/xxx
  m->outer_l2_len = sizeof(ether)
  m->outer_l3_len = sizeof(ip)
  m->l2_len = sizeof(gre)
  m->l3_len = sizeof(ip)
  m->l4_len = sizeof(udp)

Ether/IP/UDP/vxlan/Ether/IP/UDP/xxx
  m->outer_l2_len = sizeof(ether)
  m->outer_l3_len = sizeof(ip)
  m->l2_len = sizeof(udp) + sizeof(vxlan) + sizeof(ether)
  m->l3_len = sizeof(ip)
  m->l4_len = sizeof(udp)

Regards,
Olivier