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Wed, 22 Jan 2025 19:06:08 -0800 (PST) Message-ID: <09bd9f31-a096-4640-9f3e-c6232cf4b07d@gmail.com> Date: Thu, 23 Jan 2025 11:06:03 +0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH bpf-next 1/2] libbpf: Add libbpf_probe_bpf_kfunc API To: Andrii Nakryiko Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, haoluo@google.com, jolsa@kernel.org, qmo@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250122171359.232791-1-chen.dylane@gmail.com> <20250122171359.232791-2-chen.dylane@gmail.com> From: Tao Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/1/23 06:22, Andrii Nakryiko 写道: > On Wed, Jan 22, 2025 at 9:14 AM Tao Chen 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. >> >> Signed-off-by: Tao Chen >> --- >> tools/lib/bpf/libbpf.h | 16 +++++++++++++++- >> tools/lib/bpf/libbpf.map | 1 + >> tools/lib/bpf/libbpf_probes.c | 36 +++++++++++++++++++++++++++++++++++ >> 3 files changed, 52 insertions(+), 1 deletion(-) >> >> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h >> index 3020ee45303a..3b6d33578a16 100644 >> --- a/tools/lib/bpf/libbpf.h >> +++ b/tools/lib/bpf/libbpf.h >> @@ -1680,7 +1680,21 @@ LIBBPF_API int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void >> */ >> LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, >> enum bpf_func_id helper_id, const void *opts); >> - >> +/** >> + * @brief **libbpf_probe_bpf_kfunc()** detects if host kernel supports the >> + * use of a given BPF kfunc from specified BPF program type. >> + * @param prog_type BPF program type used to check the support of BPF kfunc >> + * @param kfunc_id The btf ID of BPF kfunc to check support for >> + * @param opts reserved for future extensibility, should be NULL >> + * @return 1, if given combination of program type and kfunc is supported; 0, >> + * if the combination is not supported; negative error code if feature >> + * detection for provided input arguments failed or can't be performed >> + * >> + * Make sure the process has required set of CAP_* permissions (or runs as >> + * root) when performing feature checking. >> + */ >> +LIBBPF_API int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, >> + int kfunc_id, const void *opts); >> /** >> * @brief **libbpf_num_possible_cpus()** is a helper function to get the >> * number of possible CPUs that the host kernel supports and expects. >> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map >> index a8b2936a1646..e93fae101efd 100644 >> --- a/tools/lib/bpf/libbpf.map >> +++ b/tools/lib/bpf/libbpf.map >> @@ -436,4 +436,5 @@ LIBBPF_1.6.0 { >> bpf_linker__add_buf; >> bpf_linker__add_fd; >> bpf_linker__new_fd; >> + libbpf_probe_bpf_kfunc; >> } LIBBPF_1.5.0; >> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c >> index 9dfbe7750f56..bc1cf2afbe87 100644 >> --- a/tools/lib/bpf/libbpf_probes.c >> +++ b/tools/lib/bpf/libbpf_probes.c >> @@ -413,6 +413,42 @@ int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void *opts) >> return libbpf_err(ret); >> } >> >> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, >> + const void *opts) >> +{ >> + 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); > > note how libbpf_probe_bpf_helper() rejects some program types because > they can't be really loaded. Let's keep it consistent? > Hi andrii, thank you for your guidance, i will add it later. > pw-bot: cr > >> + >> + insns[0].code = BPF_JMP | BPF_CALL; >> + insns[0].src_reg = BPF_PSEUDO_KFUNC_CALL; >> + insns[0].imm = kfunc_id; >> + >> + /* Now only support kfunc from vmlinux */ >> + insns[0].off = 0; > > why not support modules from the very beginning? > So can we add a new parameter named like "off"? If it's a module, pass the BTF offset to insns[0].off. If it's vmlinux, pass 0. >> + >> + 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 (err == 0 && strstr(buf, "not allowed")) > > Looking at kernel code, if kfunc ID is not recognized, it seems like > the verifier won't print anything, is that right? If that's the case, > then this API will behave differently from libbpf_probe_bpf_helper(), > which isn't great. > You mean kfunc id is invalid? i try set kfunc id with -1 ret = libbpf_probe_bpf_kfunc(BPF_PROG_TYPE_SYSCALL, -1, NULL); And the verifier will print like: "kernel btf_id 4294967295 is not a function" So "not a function" may also be checked, i will add it in v2. >> + 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) >> { >> -- >> 2.43.0 >> -- Best Regards Dylane Chen