From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB95FC433FE for ; Thu, 21 Apr 2022 03:40:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231693AbiDUDmv convert rfc822-to-8bit (ORCPT ); Wed, 20 Apr 2022 23:42:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1384015AbiDUDms (ORCPT ); Wed, 20 Apr 2022 23:42:48 -0400 Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC59163C0 for ; Wed, 20 Apr 2022 20:40:00 -0700 (PDT) Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.1.2/8.16.1.2) with ESMTP id 23KL3ZvN007577 for ; Wed, 20 Apr 2022 20:39:59 -0700 Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3fjsrjsy1v-4 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 20 Apr 2022 20:39:59 -0700 Received: from twshared13315.14.prn3.facebook.com (2620:10d:c085:108::8) by mail.thefacebook.com (2620:10d:c085:21d::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 20 Apr 2022 20:39:56 -0700 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id DD484186F53D6; Wed, 20 Apr 2022 20:39:50 -0700 (PDT) From: Andrii Nakryiko To: , , CC: , , Kui-Feng Lee Subject: [PATCH bpf-next 2/3] libbpf: teach bpf_link_create() to fallback to bpf_raw_tracepoint_open() Date: Wed, 20 Apr 2022 20:39:44 -0700 Message-ID: <20220421033945.3602803-3-andrii@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220421033945.3602803-1-andrii@kernel.org> References: <20220421033945.3602803-1-andrii@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-ORIG-GUID: l_LD7uXBWHRDnjOi2q8tfn8yHIZ4yXyD X-Proofpoint-GUID: l_LD7uXBWHRDnjOi2q8tfn8yHIZ4yXyD X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-04-20_06,2022-04-20_01,2022-02-23_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Teach bpf_link_create() to fallback to bpf_raw_tracepoint_open() on older kernels for programs that are attachable through BPF_RAW_TRACEPOINT_OPEN. This makes bpf_link_create() more unified and convenient interface for creating bpf_link-based attachments. With this approach end users can just use bpf_link_create() for tp_btf/fentry/fexit/fmod_ret/lsm program attachments without needing to care about kernel support, as libbpf will handle this transparently. On the other hand, as newer features (like BPF cookie) are added to LINK_CREATE interface, they will be readily usable though the same bpf_link_create() API without any major refactoring from user's standpoint. bpf_program__attach_btf_id() is now using bpf_link_create() internally as well and will take advantaged of this unified interface when BPF cookie is added for fentry/fexit. Doing proactive feature detection of LINK_CREATE support for fentry/tp_btf/etc is quite involved. It requires parsing vmlinux BTF, determining some stable and guaranteed to be in all kernels versions target BTF type (either raw tracepoint or fentry target function), actually attaching this program and thus potentially affecting the performance of the host kernel briefly, etc. So instead we are taking much simpler "lazy" approach of falling back to bpf_raw_tracepoint_open() call only if initial LINK_CREATE command fails. For modern kernels this will mean zero added overhead, while older kernels will incur minimal overhead with a single fast-failing LINK_CREATE call. Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/bpf.c | 34 ++++++++++++++++++++++++++++++++-- tools/lib/bpf/libbpf.c | 3 ++- 2 files changed, 34 insertions(+), 3 deletions(-) diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c index cf27251adb92..a9d292c106c2 100644 --- a/tools/lib/bpf/bpf.c +++ b/tools/lib/bpf/bpf.c @@ -817,7 +817,7 @@ int bpf_link_create(int prog_fd, int target_fd, { __u32 target_btf_id, iter_info_len; union bpf_attr attr; - int fd; + int fd, err; if (!OPTS_VALID(opts, bpf_link_create_opts)) return libbpf_err(-EINVAL); @@ -870,7 +870,37 @@ int bpf_link_create(int prog_fd, int target_fd, } proceed: fd = sys_bpf_fd(BPF_LINK_CREATE, &attr, sizeof(attr)); - return libbpf_err_errno(fd); + if (fd >= 0) + return fd; + /* we'll get EINVAL if LINK_CREATE doesn't support attaching fentry + * and other similar programs + */ + err = -errno; + if (err != -EINVAL) + return libbpf_err(err); + + /* if user used features not supported by + * BPF_RAW_TRACEPOINT_OPEN command, then just give up immediately + */ + if (attr.link_create.target_fd || attr.link_create.target_btf_id) + return libbpf_err(err); + if (!OPTS_ZEROED(opts, sz)) + return libbpf_err(err); + + /* otherwise, for few select kinds of programs that can be + * attached using BPF_RAW_TRACEPOINT_OPEN command, try that as + * a fallback for older kernels + */ + switch (attach_type) { + case BPF_TRACE_RAW_TP: + case BPF_LSM_MAC: + case BPF_TRACE_FENTRY: + case BPF_TRACE_FEXIT: + case BPF_MODIFY_RETURN: + return bpf_raw_tracepoint_open(NULL, prog_fd); + default: + return libbpf_err(err); + } } int bpf_link_detach(int link_fd) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 94940497354b..ae317df1fc57 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -11262,7 +11262,8 @@ static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *pro return libbpf_err_ptr(-ENOMEM); link->detach = &bpf_link__detach_fd; - pfd = bpf_raw_tracepoint_open(NULL, prog_fd); + /* libbpf is smart enough to redirect to BPF_RAW_TRACEPOINT_OPEN on old kernels */ + pfd = bpf_link_create(prog_fd, 0, bpf_program__expected_attach_type(prog), NULL); if (pfd < 0) { pfd = -errno; free(link); -- 2.30.2