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Tue, 11 Feb 2025 18:33:28 -0800 (PST) Message-ID: <49282239-350a-4a76-9243-501373009bec@gmail.com> Date: Wed, 12 Feb 2025 10:33:21 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v6 3/4] 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, Tao Chen References: <20250211111859.6029-1-chen.dylane@gmail.com> <20250211111859.6029-4-chen.dylane@gmail.com> From: Tao Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/2/12 06:24, Andrii Nakryiko 写道: > On Tue, Feb 11, 2025 at 3:19 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. >> >> Cc: Tao Chen >> Signed-off-by: Tao Chen >> --- >> tools/lib/bpf/libbpf.h | 19 +++++++++++++- >> tools/lib/bpf/libbpf.map | 1 + >> tools/lib/bpf/libbpf_probes.c | 48 +++++++++++++++++++++++++++++++++++ >> 3 files changed, 67 insertions(+), 1 deletion(-) >> >> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h >> index 3020ee45303a..e796e38cf255 100644 >> --- a/tools/lib/bpf/libbpf.h >> +++ b/tools/lib/bpf/libbpf.h >> @@ -1680,7 +1680,24 @@ 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 btf_fd The module BTF FD, if kfunc is defined in kernel module, >> + * btf_fd is used to point to module's BTF, which is >= 0, and -1 means kfunc >> + * defined in vmlinux. >> + * @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, int btf_fd, 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 b5a838de6f47..3bbfe13aeb6a 100644 >> --- a/tools/lib/bpf/libbpf.map >> +++ b/tools/lib/bpf/libbpf.map >> @@ -438,4 +438,5 @@ LIBBPF_1.6.0 { >> bpf_linker__new_fd; >> btf__add_decl_attr; >> btf__add_type_attr; >> + 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 8ed92ea922b3..ab5591c385de 100644 >> --- a/tools/lib/bpf/libbpf_probes.c >> +++ b/tools/lib/bpf/libbpf_probes.c >> @@ -431,6 +431,54 @@ static bool can_probe_prog_type(enum bpf_prog_type prog_type) >> return true; >> } >> >> +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, int btf_fd, >> + const void *opts) >> +{ >> + struct bpf_insn insns[] = { >> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 1, kfunc_id), >> + BPF_EXIT_INSN(), >> + }; >> + const size_t insn_cnt = ARRAY_SIZE(insns); >> + char buf[4096]; >> + int fd_array[2] = {-1}; >> + int ret; >> + >> + if (opts) >> + return libbpf_err(-EINVAL); >> + >> + if (!can_probe_prog_type(prog_type)) >> + return -EOPNOTSUPP; > > libbpf_err() here > > pw-bot: cr > Ack. >> + >> + if (btf_fd >= 0) { >> + fd_array[1] = btf_fd; >> + } else if (btf_fd == -1) { > > let's not hard-code the equality, use < 0 (though I'd follow > verifier's offset == 0 convention for vmlinux BTF here as well to stay > conceptually consistent) > Ack. >> + /* insn.off = 0, means vmlinux btf */ >> + insns[0].off = 0; >> + } else { >> + return libbpf_err(-EINVAL); >> + } >> + >> + 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 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, > > bpf_cpumask_create -> to keep comments generic? > >> + * it will emit "kernel btf_id 4294967295 is not a function". If btf fd > > same as above, use placeholder instead of specific number? > > and keep BTF (all caps) use consistent, please Ack. > >> + * invalid in module btf, it will emit "invalid module BTF fd specified" or > > ditto, btf -> BTF > >> + * "negative offset disallowed for kernel module function call" >> + */ >> + if (ret == 0 && (strstr(buf, "not allowed") || strstr(buf, "not a function") || >> + (strstr(buf, "invalid module BTF fd")) || >> + (strstr(buf, "negative offset disallowed")))) > > stylistically, given amount of checks, I'd probably go with the > following structure Ack. will change it. > > if (ret > 0) > return 1; > > if (strstr(buf, "not allowed") || > strstr(buf, "not a function") || > ...) > return 0; > >> + 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