linux-kernel - Re: [PATCH bpf-next v2 1/2] libbpf: Add libbpf_probe_bpf

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Message-ID: <26e2e47f-4c95-4874-969f-c497aadbb5f0@gmail.com>
Date: Fri, 24 Jan 2025 11:25:42 +0800
From: Tao Chen <chen.dylane@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>, ast@...nel.org,
 daniel@...earbox.net, andrii@...nel.org, haoluo@...gle.com,
 jolsa@...nel.org, qmo@...nel.org
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 1/2] libbpf: Add libbpf_probe_bpf_kfunc API

在 2025/1/24 09:34, Eduard Zingerman 写道:
> On Fri, 2025-01-24 at 01:05 +0800, Tao Chen wrote:
> 
> [...]
> 
>> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id,
>> +			   __s16 off, const void *opts)
>                                   ^^^
> Nit:                      maybe name this btf_fd?

Hi Eduard, thank you for your guidance, ack, i will send it in v3.

> 
>> +{
> 
> In v2 function looks identical to libbpf_probe_bpf_helper,
> do we want to copy-paste it or introduce a utility:
> 
>    static int probe_insn(enum bpf_prog_type prog_type, struct bpf_insn insn,
>                          const char **accepted_msgs)
> 
> And call it from both libbpf_probe_bpf_{helper,kfunc}?

Yes, it seems much more concise. I will send it in v3. Thanks.

> 
>> +	struct bpf_insn insns[] = {
>> +		BPF_EXIT_INSN(),
>> +		BPF_EXIT_INSN(),
>> +	};
>> +	const size_t insn_cnt = ARRAY_SIZE(insns);
>> +	int err;
>> +	char buf[4096];
>> +
>> +	if (opts)
>> +		return libbpf_err(-EINVAL);
>> +
>> +	/* Same logic as probe_bpf_helper check */
>> +	switch (prog_type) {
>> +	case BPF_PROG_TYPE_TRACING:
>> +	case BPF_PROG_TYPE_EXT:
>> +	case BPF_PROG_TYPE_LSM:
>> +	case BPF_PROG_TYPE_STRUCT_OPS:
>> +		return -EOPNOTSUPP;
>> +	default:
>> +		break;
>> +	}
>> +
>> +	insns[0].code = BPF_JMP | BPF_CALL;
>> +	insns[0].src_reg = BPF_PSEUDO_KFUNC_CALL;
>> +	insns[0].imm = kfunc_id;
>> +	insns[0].off = off;
>> +
>> +	buf[0] = '\0';
>> +	err = probe_prog_load(prog_type, insns, insn_cnt, buf, sizeof(buf));
>> +	if (err < 0)
>> +		return libbpf_err(err);
>> +
>> +	/* If BPF verifier recognizes BPF kfunc but it's not supported for
>> +	 * given BPF program type, it will emit "calling kernel function
>> +	 * bpf_cpumask_create is not allowed", if the kfunc id is invalid,
>> +	 * it will emit "kernel btf_id 4294967295 is not a function"
>> +	 */
>> +	if (err == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function")))
>> +		return 0;
>> +
>> +	return 1; /* assume supported */
>> +}
>> +
>>   int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
>>   			    const void *opts)
>>   {
> 
> 


-- 
Best Regards
Dylane Chen