Re: [PATCH bpf-next v5 2/4] bpf: core: introduce main_prog_aux for stream access

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Sep 1, 2025 at 12:37 PM Puranjay Mohan <puranjay@kernel.org> wrote:
>
> BPF streams are only valid for the main programs, to make it easier to
> access streams from subprogs, introduce main_prog_aux in struct
> bpf_prog_aux.
>
> prog->aux->main_prog_aux = prog->aux, for main programs and
> prog->aux->main_prog_aux = main_prog->aux, for subprograms.
>
> This makes it easy to access streams like:
> stream = bpf_stream_get(stream_id, prog->main_prog_aux);
>
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
> ---
>  include/linux/bpf.h   | 1 +
>  kernel/bpf/core.c     | 3 +--
>  kernel/bpf/stream.c   | 6 +++---
>  kernel/bpf/verifier.c | 1 +
>  4 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 8f6e87f0f3a89..d133171c4d2a9 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1633,6 +1633,7 @@ struct bpf_prog_aux {
>         /* function name for valid attach_btf_id */
>         const char *attach_func_name;
>         struct bpf_prog **func;
> +       struct bpf_prog_aux *main_prog_aux;
>         void *jit_data; /* JIT specific data. arch dependent */
>         struct bpf_jit_poke_descriptor *poke_tab;
>         struct bpf_kfunc_desc_tab *kfunc_tab;
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index ef01cc644a965..dbbf8e4b6e4c2 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -120,6 +120,7 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag
>
>         fp->pages = size / PAGE_SIZE;
>         fp->aux = aux;
> +       fp->aux->main_prog_aux = aux;

Though I agree that it's not strictly necessary, this approach
is so much easier to reason about.

Kumar, wdyt?