On Thu, Oct 10, 2024 at 10:56 AM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
> A kfunc bpf_prog_call() is introduced such that it can call another bpf
> prog within a bpf prog. It has the same parameters as bpf_tail_call()
> but acts like a normal function call.
>
> But bpf_prog_call() could recurse to the caller prog itself. So if a bpf
> prog calls bpf_prog_call(), that bpf prog will use private stacks with
> maximum recursion level 4. The 4 level recursion should work for most
> cases.
>
> bpf_prog_call() cannot be used if tail_call exists in the same prog
> since tail_call does not use private stack. If both prog_call and
> tail_call in the same prog, verification will fail.
..
> +__bpf_kfunc int bpf_prog_call(void *ctx, struct bpf_map *p__map, u32 index)
> +{
> + struct bpf_array *array;
> + struct bpf_prog *prog;
> +
> + if (p__map->map_type != BPF_MAP_TYPE_PROG_ARRAY)
> + return -EINVAL;
> +
> + array = container_of(p__map, struct bpf_array, map);
> + if (unlikely(index >= array->map.max_entries))
> + return -E2BIG;
> +
> + prog = READ_ONCE(array->ptrs[index]);
> + if (!prog)
> + return -ENOENT;
> +
> + return bpf_prog_run(prog, ctx);
> +}
bpf_tail_call() was a hack during the early days,
since I didn't know any better :(
I really don't want to use that as a pattern.
prog life time rules, tail call cnt, prog_array_compatible, etc.
caused plenty of pain. Don't want to see a repeat.
Progs that need to call another prog can use freplace mechanism already.
There is no need for bpf_prog_call.
Let's get priv_stack in shape first (the first ~6 patches).
pw-bot: cr
