fib/rib: allow storing void * instead of nexthop index

fib/rib: allow storing void * instead of nexthop index

[Robin Jarry]

Hi Vladimir,

I noticed that the fib/rib APIs (both IPv4 and IPv6) require the next 
hops to be represented as integer indexes. Reading the code, I noticed 
that they are stored as uint64_t with the MSB used for internal 
purposes.

This require either having a contiguous array of nexthop objects and 
choose an index in that array, or store pointer offsets as nexthop 
indexes and do pointer arithmetics to reconstruct the real pointers. 
Both are not very practical and/or hacky.

Would it be possible to store arbitrary pointers? That would mean 
moving that 64th bit information elsewhere.

I'd love to hear what you think on the matter.

Cheers,
Robin

Re: fib/rib: allow storing void * instead of nexthop index

[Medvedkin, Vladimir]

Hi Robin,


On 31/07/2024 16:04, Robin Jarry wrote:
> Hi Vladimir,
>
> I noticed that the fib/rib APIs (both IPv4 and IPv6) require the next 
> hops to be represented as integer indexes. Reading the code, I noticed 
> that they are stored as uint64_t with the MSB used for internal purposes.

I believe you are asking about FIB, not RIB. In current FIB 
implementation 1 LSB is used for internal purposes.


>
> This require either having a contiguous array of nexthop objects and 
> choose an index in that array,

As far as I know that's what most of "l3 forward" applications (aka 
routers) are doing, if they are interested in performance. Not only DPDK 
powered.


> or store pointer offsets as nexthop indexes and do pointer arithmetics 
> to reconstruct the real pointers. Both are not very practical and/or 
> hacky.
>
> Would it be possible to store arbitrary pointers? That would mean 
> moving that 64th bit information elsewhere.

For arbitrary pointer - no, since it needs to store 1 more bit for 
internal purpose. However, if you have 2 byte aligned pointer you can 
store the pointer shifted right by 1 bit, and after lookup just shift 
the result back.


>
> I'd love to hear what you think on the matter.
>
> Cheers,
> Robin
>
-- 
Regards,
Vladimir