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 X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 265AEC07E9C for ; Wed, 7 Jul 2021 20:52:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0E04C61CD2 for ; Wed, 7 Jul 2021 20:52:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231981AbhGGUz0 (ORCPT ); Wed, 7 Jul 2021 16:55:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42082 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230229AbhGGUzZ (ORCPT ); Wed, 7 Jul 2021 16:55:25 -0400 Received: from mail-yb1-xb29.google.com (mail-yb1-xb29.google.com [IPv6:2607:f8b0:4864:20::b29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 75C80C061574; Wed, 7 Jul 2021 13:52:44 -0700 (PDT) Received: by mail-yb1-xb29.google.com with SMTP id b13so5331915ybk.4; Wed, 07 Jul 2021 13:52:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Sk8sHu6LCd2EXAfBmiWFJrRWB8lEE1Gj41aKiaDQM8M=; b=IeNuCJJp9EceruFg/UtNe/J+C+vGnrAAXxtxF0a29KPcNHcffU3owIxVBqcArpI7vc T/SGJA1iooGK46dgHVKnAiN42fEB1ZnJNw2+qb5MDYVoMQxKlc2BeLs5S7NEM21rz+OW 58waRJ+T8wLhKzooBNsq33aWZ9/yEKDTpOsSMAII27J/c7zCDNSNavLw2642J6TrtNPM 2giOI0BCwIBoCs+zxlYn5tt0lYuRklOnseWEM8/hDf27zo7nHIN6CGkvBMUhRUp3eAng 1Fufm/SjQAdQzeo/ZB9QZbvfJuhHIk9ek27MtHLt/tSa/VGatsaMkQ2c2Yr2Q1PeIy2D ynbw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Sk8sHu6LCd2EXAfBmiWFJrRWB8lEE1Gj41aKiaDQM8M=; b=foOoBqoJ4C7Uvb6B94+6ZF26ptGWIWgd9hYADOtrJ90jBWLbucatv5kwMVrPmoyMMa CS3SrYHnaasBQW2a4hswF0opxBlOMimyxY59Xhz494eYzNdNg502rZDLA1VvATnrmqRO IFCul7oECshMv+XRXO8O/aFJPR8jdkYHTiJj/jyvNukYztsarDfotGFSGufp4FTD8AhK cGkh2LfYZNWo/xBUZwX7x13rAMLzezm4OZgFv2sTnq6y5rCKny4bgqB22E9o+/1BqcRZ j4/OrAcHTExW4OnYaaZkdfZlnJb82IeNfzg+pM8Dpsa/psZyU7GZMQzPX5uQfYwYarPw qKJw== X-Gm-Message-State: AOAM530v7jn3HJbR3r2Kv0rvtSCut5OtYdZ4nO6NNLfpyQKO5IlRD+pG oDOvN34u4UWzn4TxnefRZMeWjpv0Zo3IfVud+rA= X-Google-Smtp-Source: ABdhPJyBSIXwel6YwRDisY/XdfX9ohxrKOhqrd6iG8lRYS3BKYhBicfPBRmYGXQKj+RWQMulNGJCA+iWIo+8VdNDOD0= X-Received: by 2002:a25:9942:: with SMTP id n2mr34854535ybo.230.1625691163601; Wed, 07 Jul 2021 13:52:43 -0700 (PDT) MIME-Version: 1.0 References: <1624507409-114522-1-git-send-email-chengshuyi@linux.alibaba.com> In-Reply-To: <1624507409-114522-1-git-send-email-chengshuyi@linux.alibaba.com> From: Andrii Nakryiko Date: Wed, 7 Jul 2021 13:52:32 -0700 Message-ID: Subject: Re: [PATCH bpf-next] libbpf: Introduce 'custom_btf_path' to 'bpf_obj_open_opts'. To: Shuyi Cheng Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin Lau , Song Liu , Yonghong Song , john fastabend , KP Singh , Networking , bpf , open list , kernel-janitors@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 23, 2021 at 9:04 PM Shuyi Cheng wrote: > > In order to enable the older kernel to use the CO-RE feature, load the > vmlinux btf of the specified path. > > Learn from Andrii's comments in [0], add the custom_btf_path parameter > to bpf_obj_open_opts, you can directly use the skeleton's > _bpf__open_opts function to pass in the custom_btf_path > parameter. > > Prior to this, there was also a developer who provided a patch with > similar functions. It is a pity that the follow-up did not continue to > advance. See [1]. > > [0]https://lore.kernel.org/bpf/CAEf4BzbJZLjNoiK8_VfeVg_Vrg=9iYFv+po-38SMe=UzwDKJ=Q@mail.gmail.com/#t > [1]https://yhbt.net/lore/all/CAEf4Bzbgw49w2PtowsrzKQNcxD4fZRE6AKByX-5-dMo-+oWHHA@mail.gmail.com/ > > Signed-off-by: Shuyi Cheng > --- > tools/lib/bpf/libbpf.c | 23 ++++++++++++++++++++--- > tools/lib/bpf/libbpf.h | 6 +++++- > 2 files changed, 25 insertions(+), 4 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 1e04ce7..518b19f 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -509,6 +509,8 @@ struct bpf_object { > void *priv; > bpf_object_clear_priv_t clear_priv; > > + char *custom_btf_path; > + > char path[]; > }; > #define obj_elf_valid(o) ((o)->efile.elf) > @@ -2679,8 +2681,15 @@ static int bpf_object__load_vmlinux_btf(struct bpf_object *obj, bool force) > if (!force && !obj_needs_vmlinux_btf(obj)) > return 0; > > - obj->btf_vmlinux = libbpf_find_kernel_btf(); > - err = libbpf_get_error(obj->btf_vmlinux); > + if (obj->custom_btf_path) { > + obj->btf_vmlinux = btf__parse(obj->custom_btf_path, NULL); > + err = libbpf_get_error(obj->btf_vmlinux); > + pr_debug("loading custom vmlinux BTF '%s': %d\n", obj->custom_btf_path, err); > + } else { > + obj->btf_vmlinux = libbpf_find_kernel_btf(); > + err = libbpf_get_error(obj->btf_vmlinux); > + } I think it will be more flexible to treat custom_btf as an vmlinux BTF override, just like [1] did. I can see how in some situations users might want to treat this custom BTF as either a replacement of vmlinux BTF or as an augmentation of vmlinux BTF for the purpose of extra custom CO-RE relocations (e.g., something along the XDP hints that were discussed recently). For now it's probably enough to implement "custom BTF is a replacement for vmlinux BTF" policy and, if necessary, add "custom BTF is in addition to vmlinux BTF" later with extra opts flag/field. Keep in mind that this custom BTF is only useful for BPF CO-RE relocation. Any other kernel feature relying on vmlinux BTF (e.g., fentry) won't work with custom BTF because it expects correct BTF type IDs. > + > if (err) { > pr_warn("Error loading vmlinux BTF: %d\n", err); > obj->btf_vmlinux = NULL; > @@ -7554,7 +7563,7 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver) > __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz, > const struct bpf_object_open_opts *opts) > { > - const char *obj_name, *kconfig; > + const char *obj_name, *kconfig, *tmp_btf_path; > struct bpf_program *prog; > struct bpf_object *obj; > char tmp_name[64]; > @@ -7584,6 +7593,13 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver) > obj = bpf_object__new(path, obj_buf, obj_buf_sz, obj_name); > if (IS_ERR(obj)) > return obj; > + > + tmp_btf_path = OPTS_GET(opts, custom_btf_path, NULL); > + if (tmp_btf_path && strlen(tmp_btf_path) < PATH_MAX) { if strlen() is >= PATH_MAX you'll just silently ignore it? We should either truncate silently (because PATH_MAX is totally reasonable assumption) or error out. > + obj->custom_btf_path = strdup(tmp_btf_path); > + if (!obj->custom_btf_path) > + return ERR_PTR(-ENOMEM); > + } > > kconfig = OPTS_GET(opts, kconfig, NULL); > if (kconfig) { > @@ -8702,6 +8718,7 @@ void bpf_object__close(struct bpf_object *obj) > for (i = 0; i < obj->nr_maps; i++) > bpf_map__destroy(&obj->maps[i]); > > + zfree(&obj->custom_btf_path); > zfree(&obj->kconfig); > zfree(&obj->externs); > obj->nr_extern = 0; > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > index 6e61342..16e0f01 100644 > --- a/tools/lib/bpf/libbpf.h > +++ b/tools/lib/bpf/libbpf.h > @@ -94,8 +94,12 @@ struct bpf_object_open_opts { > * system Kconfig for CONFIG_xxx externs. > */ > const char *kconfig; > + /* Specify the path of vmlinux btf to facilitate the use of CO-RE features > + * in the old kernel. > + */ > + char *custom_btf_path; > }; > -#define bpf_object_open_opts__last_field kconfig > +#define bpf_object_open_opts__last_field custom_btf_path > > LIBBPF_API struct bpf_object *bpf_object__open(const char *path); > LIBBPF_API struct bpf_object * > -- > 1.8.3.1 >