linux-kernel - Re: [PATCH v4 bpf-next 1/2] bpf: add a ksym BPF iterator

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Date:   Fri, 8 Jul 2022 16:17:10 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     ast@...nel.org, andrii@...nel.org, daniel@...earbox.net,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, jolsa@...nel.org,
        mhiramat@...nel.org, akpm@...ux-foundation.org, void@...ifault.com,
        swboyd@...omium.org, ndesaulniers@...gle.com,
        9erthalion6@...il.com, kennyyu@...com, geliang.tang@...e.com,
        kuniyu@...zon.co.jp, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 bpf-next 1/2] bpf: add a ksym BPF iterator

Hi Alan,

On Wed, Jul 6, 2022 at 6:17 AM Alan Maguire <alan.maguire@...cle.com> wrote:
>
> add a "ksym" iterator which provides access to a "struct kallsym_iter"
> for each symbol.  Intent is to support more flexible symbol parsing
> as discussed in [1].
>
> [1] https://lore.kernel.org/all/YjRPZj6Z8vuLeEZo@krava/
>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> Acked-by: Yonghong Song <yhs@...com>
> ---
>  kernel/kallsyms.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
>
[...]
> +
> +static struct bpf_iter_reg ksym_iter_reg_info = {
> +       .target                 = "ksym",
> +       .ctx_arg_info_size      = 1,
> +       .ctx_arg_info           = {
> +               { offsetof(struct bpf_iter__ksym, ksym),
> +                 PTR_TO_BTF_ID_OR_NULL },
> +       },
> +       .seq_info               = &ksym_iter_seq_info,
> +};
> +

Can we add allow resched here?

 .feature = BPF_ITER_RESCHED,

I think this will improve the responsiveness of the kernel when iterating ksyms.

Thanks,
Hao

> +BTF_ID_LIST(btf_ksym_iter_id)
> +BTF_ID(struct, kallsym_iter)
> +
> +static int __init bpf_ksym_iter_register(void)
> +{
> +       int ret;
> +
> +       ksym_iter_reg_info.ctx_arg_info[0].btf_id = *btf_ksym_iter_id;
> +       ret = bpf_iter_reg_target(&ksym_iter_reg_info);
> +       if (ret)
> +               pr_warn("Warning: could not register bpf ksym iterator: %d\n", ret);
> +       return ret;
> +}
> +
> +late_initcall(bpf_ksym_iter_register);
> +
> +#endif /* CONFIG_BPF_SYSCALL */
> +
>  static inline int kallsyms_for_perf(void)
>  {
>  #ifdef CONFIG_PERF_EVENTS
> --
> 1.8.3.1
>