Re: [dpdk-dev] [PATCH v4 3/3] mbuf:replace the inner_l2_len and the inner_l3_len fields

["didier.pallard" <didier.pallard@6wind.com>]

Hello,

On 12/02/2014 07:52 AM, Jijiang Liu wrote:
> Replace the inner_l2_len and the inner_l3_len field with the outer_l2_len and outer_l3_len field, and rework csum forward engine and i40e PMD due to  these changes.
>
> Signed-off-by: Jijiang Liu <jijiang.liu@intel.com>
[...]
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -276,8 +276,8 @@ struct rte_mbuf {
>   			uint64_t tso_segsz:16; /**< TCP TSO segment size */
>   
>   			/* fields for TX offloading of tunnels */
> -			uint64_t inner_l3_len:9; /**< inner L3 (IP) Hdr Length. */
> -			uint64_t inner_l2_len:7; /**< inner L2 (MAC) Hdr Length. */
> +			uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr Length. */
> +			uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr Length. */
>   
>   			/* uint64_t unused:8; */
>   		};

Sorry for entering lately this discussion, but i'm not convinced by the 
choice of outer_lx_len rather than inner_lx_len for new fields.
I agree with Olivier that new flags should only be related to the use of 
new fields, to maintain coherency with oldest implementations.
But from a stack point of view, i think it is better to have lx_len 
fields that target the outer layers, and to name new fields inner_lx_len.

Let's discuss the two possibilities.

1) outer_lx_len fields are introduced.
In this case, the stack should have knowledge that it is processing 
tunneled packets to use outer_lx_len rather than lx_len,
or stack should always use outer_lx_len packet and move those fields to 
lx_len packets if no tunneling occurs...
I think it will induce extra processing that does not seem to be really 
needed.

2) inner_lx_len fields are introduced.
In this case, the stack first uses lx_len fields. When packet should be 
tunneled, lx_len fields are moved to inner_lx_len fields.
Then the stack can process the outer layer and still use the lx_len fields.

For  example:
an eth/IP/TCP forged packet will look like this:

Ether/IP/UDP/xxx
   m->flags = IP_CKSUM
   m->l2_len = sizeof(ether)
   m->l3_len = sizeof(ip)
   m->l4_len = sizeof(udp)
   m->inner_l2_len = 0
   m->inner_l3_len = 0

When entering tunnel for example a VXLAN interface, lx_len will be moved 
to inner_lx_len

Ether/IP/UDP/xxx
   m->flags = INNER_IP_CKSUM
   m->l2_len = 0
   m->l3_len = 0
   m->l4_len = 0
   m->inner_l2_len = sizeof(ether)
   m->inner_l3_len = sizeof(ip)
  

once complete encapsulation is processed by the stack, the packet will 
look like

Ether/IP/UDP/VXLAN/Ether/IP/UDP/xxx
   m->flags = IP_CKSUM | INNER_IP_CKSUM
   m->l2_len = sizeof(ether)
   m->l3_len = sizeof(ip)
   m->l4_len = sizeof(udp)
   m->inner_l2_len = sizeof(ether) + sizeof (vxlan)
   m->inner_l3_len = sizeof(ip)


didier