Re: [PATCH bpf-next v4 05/11] bpf: Enable TCP congestion control kfunc from modules

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, "Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	Networking <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v4 05/11] bpf: Enable TCP congestion control kfunc from modules
Date: Tue, 21 Sep 2021 15:18:55 -0700	[thread overview]
Message-ID: <CAEf4BzY7EVKv66CZ9KfefDopWDPL7xQCgLxq=oDS3eLKusAHWA@mail.gmail.com> (raw)
In-Reply-To: <20210920141526.3940002-6-memxor@gmail.com>

On Mon, Sep 20, 2021 at 7:15 AM Kumar Kartikeya Dwivedi
<memxor@gmail.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 resolve_btfids in TCP congestion control modules if the config option
> is set, using the base BTF support added in the previous commit.
>
> 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)
>
> [ resolve_btfids uses --no-fail because some crypto kernel modules
>   under arch/x86/crypto generated from ASM do not have the .BTF sections ]
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.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(-)
>

[...]

> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index ff805777431c..b4f83533eda6 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -41,6 +41,7 @@ quiet_cmd_btf_ko = BTF [M] $@
>        cmd_btf_ko =                                                     \
>         if [ -f vmlinux ]; then                                         \
>                 LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J --btf_base vmlinux $@; \
> +               $(RESOLVE_BTFIDS) --no-fail -s vmlinux $@;              \

I think I've asked that before, but I don't remember this being
answered. Why is this --no-fail?

>         else                                                            \
>                 printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
>         fi;
> --
> 2.33.0
>