linux-kernel - Re: Re: [PATCH bpf-next] samples/bpf: Fix sockex3: missing BPF prog type

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Date:   Fri, 4 Nov 2022 15:53:09 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Rong Tao <rtoax@...mail.com>
Cc:     andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        daniel@...earbox.net, haoluo@...gle.com, john.fastabend@...il.com,
        jolsa@...nel.org, kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        martin.lau@...ux.dev, rongtao@...tc.cn, sdf@...gle.com,
        song@...nel.org, yhs@...com
Subject: Re: Re: [PATCH bpf-next] samples/bpf: Fix sockex3: missing BPF prog type

On Thu, Nov 3, 2022 at 8:17 PM Rong Tao <rtoax@...mail.com> wrote:
>
> We can not just remove the number of program like:
>
> -#define PROG(F) SEC("socket/"__stringify(F)) int bpf_func_##F
> +#define PROG(F) SEC("socket_filter") int bpf_func_##F
>
> because "sockex3" use the _NUMBER_ as index(see map "jmp_table"), if we
> apply the following patch, it's still not recognize "socket_filter/xxx"
> as "socket_filter", still have "missing BPF prog type" error:

Ok, let's keep unwinding this. This is an old and manual way to set up
tail call map. Libbpf supports declarative way to do, so
sockex3_user.c won't have to do anything at all.

See progs/test_prog_array_init.c for an example. Let's convert samples
to use this as well.

This programmatic setting of program type works, there is no doubt
about this. But it's a signal that something is not exactly how it
should be. So let's use this as an opportunity to modernize samples,
instead of adding workarounds.

I hope you sympathize with this goal.

>
> diff --git a/samples/bpf/sockex3_kern.c b/samples/bpf/sockex3_kern.c
> index b363503357e5..ab5a7bde66d0 100644
> --- a/samples/bpf/sockex3_kern.c
> +++ b/samples/bpf/sockex3_kern.c
> @@ -17,7 +17,7 @@
>  #define IP_MF          0x2000
>  #define IP_OFFSET      0x1FFF
>

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