linux-kernel - Re: [PATCH bpf-next v8 3/5] libbpf: Add libbpf_probe_bpf

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Message-ID: <edec731d-3370-46b8-baad-b8bf181bcce3@linux.dev>
Date: Tue, 25 Feb 2025 13:47:38 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 eddyz87@...il.com, haoluo@...gle.com, jolsa@...nel.org, qmo@...nel.org,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org, chen.dylane@...il.com,
 Tao Chen <dylane.chen@...iglobal.com>
Subject: Re: [PATCH bpf-next v8 3/5] libbpf: Add libbpf_probe_bpf_kfunc API

在 2025/2/25 09:15, Andrii Nakryiko 写道:
> On Mon, Feb 24, 2025 at 9:02 AM Tao Chen <chen.dylane@...ux.dev> wrote:
>>
>> Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc
>> used to test the availability of the different eBPF kfuncs on the
>> current system.
>>
>> Cc: Tao Chen <dylane.chen@...iglobal.com>
>> Reviewed-by: Jiri Olsa <jolsa@...nel.org>
>> Reviewed-by: Eduard Zingerman <eddyz87@...il.com>
>> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
>> ---
>>   tools/lib/bpf/libbpf.h        | 19 ++++++++++++-
>>   tools/lib/bpf/libbpf.map      |  1 +
>>   tools/lib/bpf/libbpf_probes.c | 51 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 70 insertions(+), 1 deletion(-)
>>
> 
> [...]
> 
>> +       buf[0] = '\0';
>> +       ret = probe_prog_load(prog_type, insns, insn_cnt, btf_fd >= 0 ? fd_array : NULL,
>> +                             buf, sizeof(buf));
>> +       if (ret < 0)
>> +               return libbpf_err(ret);
>> +
>> +       if (ret > 0)
>> +               return 1; /* assume supported */
>> +
>> +       /* If BPF verifier recognizes BPF kfunc but it's not supported for
>> +        * given BPF program type, it will emit "calling kernel function
>> +        * <name> is not allowed". If the kfunc id is invalid,
>> +        * it will emit "kernel btf_id <id> is not a function". If BTF fd
>> +        * invalid in module BTF, it will emit "invalid module BTF fd specified" or
>> +        * "negative offset disallowed for kernel module function call". If
>> +        * kfunc prog not dev buound, it will emit "metadata kfuncs require
>> +        * device-bound program".
>> +        */
>> +       if (strstr(buf, "not allowed") || strstr(buf, "not a function") ||
>> +          strstr(buf, "invalid module BTF fd") ||
> 
> why is invalid module BTF FD not an error (negative return)?
> 
>> +          strstr(buf, "negative offset disallowed") ||
>> +          strstr(buf, "device-bound program"))
>> +               return 0;
>> +
>> +       return 1;
>> +}
>> +
>>   int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>>                              const void *opts)
>>   {
>> --
>> 2.43.0
>>

In probe_prog_load, err will be checked and converted into either 0 or 1.

-- 
Best Regards
Tao Chen