netdev - Re: [PATCH bpf-next v6 5/9] bpf: Enable TCP congestion control kfunc from modules

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Date:   Fri, 1 Oct 2021 14:14:54 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v6 5/9] bpf: Enable TCP congestion control kfunc
 from modules

On Wed, Sep 29, 2021 at 11:30 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>
> This commit moves BTF ID lookup into the newly added registration
> helper, in a way that the bbr, cubic, and dctcp implementation set up
> their sets in the bpf_tcp_ca kfunc_btf_set list, while the ones not
> dependent on modules are looked up from the wrapper function.
>
> This lifts the restriction for them to be compiled as built in objects,
> and can be loaded as modules if required. Also modify Makefile.modfinal
> to call resolve_btfids for each module.
>
> Note that since kernel kfunc_ids never overlap with module kfunc_ids, we
> only match the owner for module btf id sets.
>
> See following commits for background on use of:
>
>  CONFIG_X86 ifdef:
>  569c484f9995 (bpf: Limit static tcp-cc functions in the .BTF_ids list to x86)
>
>  CONFIG_DYNAMIC_FTRACE ifdef:
>  7aae231ac93b (bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE)
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> ---
>  include/linux/btf.h       |  4 ++++
>  kernel/bpf/btf.c          |  3 +++
>  net/ipv4/bpf_tcp_ca.c     | 34 +++-------------------------------
>  net/ipv4/tcp_bbr.c        | 28 +++++++++++++++++++++++++++-
>  net/ipv4/tcp_cubic.c      | 26 +++++++++++++++++++++++++-
>  net/ipv4/tcp_dctcp.c      | 26 +++++++++++++++++++++++++-
>  scripts/Makefile.modfinal |  1 +
>  7 files changed, 88 insertions(+), 34 deletions(-)
>

[...]

>  BTF_SET_END(bpf_tcp_ca_kfunc_ids)
>
>  static bool bpf_tcp_ca_check_kfunc_call(u32 kfunc_btf_id, struct module *owner)
>  {
> -       return btf_id_set_contains(&bpf_tcp_ca_kfunc_ids, kfunc_btf_id);
> +       if (btf_id_set_contains(&bpf_tcp_ca_kfunc_ids, kfunc_btf_id))
> +               return true;
> +       return __bpf_tcp_ca_check_kfunc_call(kfunc_btf_id, owner);

so here, why it can't be generic

__bpf_check_kfunc_call(&bpf_tcp_ca_kfunc_list, kfunc_btf_id, owner);

?

>  }
>
>  static const struct bpf_verifier_ops bpf_tcp_ca_verifier_ops = {

[...]