[dash-p4] Add tunnel member table and tunnel next hop table.

[r12f]

To support the ECMP group in the tunnel, this change adds the tunnel member and tunnel next hop tables using the same way as how next hop group works today in SAI.

The detailed design is following the HLD defined here: https://github.com/sonic-net/DASH/blob/main/documentation/private-link-service/private-link-service.md.

[r12f]

hi @prsunny , here is the preview of the tunnel member and next hop change. please let me know, if you have any concerns. The API should be ok, and I will get the P4 part a bit more stable in the meantime.

[prsunny]

lgtm

[mukeshmv]

@r12f , @prsunny this ECMP API design with tunnel nexthops and tunnel members being pushed iteratively is very hard to implement in the pipeline. Ideally we need to be able to pre-allocate the resources for each ECMP group when the group is created.

[r12f]

hi @mukeshmv , the tunnel design follows exactly the same pattern as the current SAI next hop group and next hop design. If preallocation is required, we can ensure the tunnel next hops are all created before bind the tunnel to any mappings. And after that, the next hop list will not be change. This should solve the problem.

However, we do have case there tunnel next hops being changed, say a destination being removed. Without certain support, this can fundamentally break certain scenarios. So let's touch base offline and see how to get this supported.

[r12f]

Actually, after second thought, this might be related to the hash distribution thing, not the actual element count. Adding a size should help. Yea, we can add that. I will push a new PR late today.

[KrisNey-MSFT]

Looks ready to merge

[mukeshmv]

@prsunny Can you please specify the scale parameters for these objects in the HLD
number of DASH_TUNNEL objects,
number of members per DASH_TUNNEL object.

[prsunny]

@prsunny Can you please specify the scale parameters for these objects in the HLD number of DASH_TUNNEL objects, number of members per DASH_TUNNEL object.

@mukeshmv , the following are the scale we are thinking:

1. DASH_TUNNEL - 1k per dpu
2. MEMBER scale - 128

Will update the sonic-hld for this scale numbers

[mukeshmv]

lgtm