From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2D2032773E3; Fri, 16 Jan 2026 13:58:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768571900; cv=none; b=C7nD3PVWeqIToDkXNKuuTXULYbBdZE9y3bcEBdeOlh2ObHC5+0gNuhL7eTz5ry9X2TVzInGjAjZukp+7LX01yErSG4tcYD0jz4s732mEVUP0zJ5i5WJBPx1wukp9ZFlCgfnozGJGj1ovN6OJIk1Lk+rUv+aQKm0Vct0KBOGs5Ts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768571900; c=relaxed/simple; bh=tp/RuFxl25c/3MAHh/OGbpkoPnnqRe0fleAQ03AG4lc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DaFvKx+AQHu6MvF/noCIvJ1cfihyVXVjsVA38ssZ3FbkaH3sJ5TbfxST/yDxM9JOhJwKwlEl7F0JawU5nl6bWsa63Ox+RX/tpQisExt7vA2W49ACzhspXFrZ6CRmquIUDb5Rap7Qo78b4txc0eJxmOp5U5lHWaLyIyiWoXFHmzg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=unEYD31Y; arc=none smtp.client-ip=95.215.58.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="unEYD31Y" Message-ID: <3b0fa14d-a11d-4ed7-8f28-2e99d74f6b46@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1768571887; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Im3pXRquGmKg1XDHvYG50pWNpmpor53XZzJQHnENrGo=; b=unEYD31YS7QXZeQ/1xU7bRf697wc8+qsW4C791IXzV19kwBtQnh7DpvcxQko0VpUdrGKyG zl+uimAv7RvYE+Hzzpq0tDD/LLu20sw+sjUyXSzuhu+QOrqnBjfIMAlen8melDzEYBMScy 9mmSBX9VyyK8MBI6Ilf4YWjqrBGJXv4= Date: Fri, 16 Jan 2026 21:57:47 +0800 Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v5 2/9] libbpf: Add support for extended bpf syscall To: Andrii Nakryiko Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Christian Brauner , Seth Forshee , Yuichiro Tsuji , Andrey Albershteyn , Willem de Bruijn , Jason Xing , Tao Chen , Mykyta Yatsenko , Kumar Kartikeya Dwivedi , Anton Protopopov , Amery Hung , Rong Tao , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-patches-bot@fb.com References: <20260112145616.44195-1-leon.hwang@linux.dev> <20260112145616.44195-3-leon.hwang@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2026/1/16 08:42, Andrii Nakryiko wrote: > On Mon, Jan 12, 2026 at 6:58 AM Leon Hwang wrote: >> >> To support the extended BPF syscall introduced in the previous commit, >> introduce the following internal APIs: >> >> * 'sys_bpf_ext()' >> * 'sys_bpf_ext_fd()' >> They wrap the raw 'syscall()' interface to support passing extended >> attributes. >> * 'probe_sys_bpf_ext()' >> Check whether current kernel supports the extended attributes. >> >> Signed-off-by: Leon Hwang >> --- >> tools/lib/bpf/bpf.c | 34 +++++++++++++++++++++++++++++++++ >> tools/lib/bpf/features.c | 8 ++++++++ >> tools/lib/bpf/libbpf_internal.h | 3 +++ >> 3 files changed, 45 insertions(+) >> >> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c >> index 21b57a629916..d44e667aaf02 100644 >> --- a/tools/lib/bpf/bpf.c >> +++ b/tools/lib/bpf/bpf.c >> @@ -69,6 +69,40 @@ static inline __u64 ptr_to_u64(const void *ptr) >> return (__u64) (unsigned long) ptr; >> } >> >> +static inline int sys_bpf_ext(enum bpf_cmd cmd, union bpf_attr *attr, >> + unsigned int size, >> + struct bpf_common_attr *common_attr, > > nit: kernel uses consistent attr_common/size_common pattern, but here > you are inverting attr_common -> common_attr, let's not? > Ack. I'll keep the same pattern. >> + unsigned int size_common) >> +{ >> + cmd = common_attr ? (cmd | BPF_COMMON_ATTRS) : (cmd & ~BPF_COMMON_ATTRS); >> + return syscall(__NR_bpf, cmd, attr, size, common_attr, size_common); >> +} >> + >> +static inline int sys_bpf_ext_fd(enum bpf_cmd cmd, union bpf_attr *attr, >> + unsigned int size, >> + struct bpf_common_attr *common_attr, >> + unsigned int size_common) >> +{ >> + int fd; >> + >> + fd = sys_bpf_ext(cmd, attr, size, common_attr, size_common); >> + return ensure_good_fd(fd); >> +} >> + >> +int probe_sys_bpf_ext(void) >> +{ >> + const size_t attr_sz = offsetofend(union bpf_attr, prog_token_fd); >> + union bpf_attr attr; >> + int fd; >> + >> + memset(&attr, 0, attr_sz); >> + fd = syscall(__NR_bpf, BPF_PROG_LOAD | BPF_COMMON_ATTRS, &attr, attr_sz, NULL, >> + sizeof(struct bpf_common_attr)); >> + if (fd >= 0) >> + close(fd); > > hm... close can change errno, this is fragile. If fd >= 0, something > is wrong with our detection, just return error right away? > How about capture errno before closing? err = errno; if (fd >= 0) close(fd); return err = EFAULT; Then, we can wrap all details in probe_sys_bpf_ext(). >> + return errno == EFAULT; >> +} >> + >> static inline int sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr, >> unsigned int size) >> { >> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c >> index b842b83e2480..d786a815f1ae 100644 >> --- a/tools/lib/bpf/features.c >> +++ b/tools/lib/bpf/features.c >> @@ -506,6 +506,11 @@ static int probe_kern_arg_ctx_tag(int token_fd) >> return probe_fd(prog_fd); >> } >> >> +static int probe_kern_extended_syscall(int token_fd) >> +{ >> + return probe_sys_bpf_ext(); >> +} >> + >> typedef int (*feature_probe_fn)(int /* token_fd */); >> >> static struct kern_feature_cache feature_cache; >> @@ -581,6 +586,9 @@ static struct kern_feature_desc { >> [FEAT_BTF_QMARK_DATASEC] = { >> "BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec, >> }, >> + [FEAT_EXTENDED_SYSCALL] = { >> + "Kernel supports extended syscall", probe_kern_extended_syscall, > > "extended syscall" is a bit vague... We specifically detect common > attrs support, maybe say that? > Ack. I'll update it to "BPF syscall common attributes support." >> + }, >> }; >> >> bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id) >> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h >> index fc59b21b51b5..e2a6ef4b45ae 100644 >> --- a/tools/lib/bpf/libbpf_internal.h >> +++ b/tools/lib/bpf/libbpf_internal.h >> @@ -392,6 +392,8 @@ enum kern_feature_id { >> FEAT_ARG_CTX_TAG, >> /* Kernel supports '?' at the front of datasec names */ >> FEAT_BTF_QMARK_DATASEC, >> + /* Kernel supports extended syscall */ >> + FEAT_EXTENDED_SYSCALL, > > FEAT_BPF_COMMON_ATTRS ? > FEAT_BPF_SYSCALL_COMMON_ATTRS seems more accurate. Thanks, Leon >> __FEAT_CNT, >> }; >> >> @@ -757,4 +759,5 @@ int probe_fd(int fd); >> #define SHA256_DWORD_SIZE SHA256_DIGEST_LENGTH / sizeof(__u64) >> >> void libbpf_sha256(const void *data, size_t len, __u8 out[SHA256_DIGEST_LENGTH]); >> +int probe_sys_bpf_ext(void); >> #endif /* __LIBBPF_LIBBPF_INTERNAL_H */ >> -- >> 2.52.0 >>