Re: [PATCH gwproxy v8 2/2] gwproxy: refactor code base to add experimental raw DNS backend

[Ahmad Gani <reyuki@gnuweeb.org>]

On Sun, Sep 7, 2025 at 11:23 AM Ammar Faizi wrote:
> Have these two structs:
>
> struct stack_u16 {
>         uint16_t sp;
>         uint16_t bp;
>         uint16_t *arr;
> };
>
> struct dns_resolver {
>         struct stack_u16 stack;
>         struct gwp_conn_pair **sess_map;
>         uint16_t sess_map_cap;
> };
>
> [ The struct dns_resolver MAY also cover socket, addr, etc. Now my
>   primary point here is about the session mapping data structure. ]
>
> 1) @stack is used to keep track of unused indexes in @sess_map.
>
>    - Push all unused indexes into the @stack, the index will be used as
>      the DNS query txid.
>
>    - When creating a DNS query, pop the stack, use the popped number as
>      the txid. The txid is also used to store the corresponding
>      gwp_conn_pair session (sess_map[txid] = ptr to conn session).
>
>    - When the sess_map[txid] is no longer used, set
>      (sess_map[txid] = NULL) and push the txid back into the @stack.

Could you elaborate on the usage of bp and sp? I'm a bit confused about
how they are intended to be used in practice.

My assumption is that bp points to index 0 as the base, and sp points to
index sess_map_cap - 1. Is that correct? If so, why do we need bp in the
first place, under what circumstances would bp change to something else?

> - Double the size when the slot is exhausted. When double-ing the
> size, the new allocated indexes are all pushed into the @stack.
> The slot exhaustion happens when the @stack is empty, it can be
> identified at the pop operation.

So the @stack.arr is considered to be empty when sp == bp or zero
and at that moment, no more txid left to be used for incoming queries.

> If the number of elements in the @stack is
> equal to @sess_map_cap, that means @sess_map is 100% free and can
> be reset to the initial state (back to size 16).

Because I treat @stack.sp as an index that gets incremented gradually
each time a push operation occurs, I assume you're talking about
@stack.sp + 1 == @sess_map_cap.

--
Ahmad Gani