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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 2071DC49EAB for ; Thu, 24 Jun 2021 15:06:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1036C613DA for ; Thu, 24 Jun 2021 15:06:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232405AbhFXPJQ (ORCPT ); Thu, 24 Jun 2021 11:09:16 -0400 Received: from www62.your-server.de ([213.133.104.62]:40620 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232053AbhFXPJE (ORCPT ); Thu, 24 Jun 2021 11:09:04 -0400 Received: from sslproxy05.your-server.de ([78.46.172.2]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1lwQwA-000Ecy-3N; Thu, 24 Jun 2021 17:06:38 +0200 Received: from [85.7.101.30] (helo=linux-3.home) by sslproxy05.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1lwQw9-000Cue-Ro; Thu, 24 Jun 2021 17:06:37 +0200 Subject: Re: [PATCH bpf-next] libbpf: Introduce 'custom_btf_path' to 'bpf_obj_open_opts'. To: Shuyi Cheng , ast@kernel.org, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org References: <1624507409-114522-1-git-send-email-chengshuyi@linux.alibaba.com> From: Daniel Borkmann Message-ID: <8ca15bab-ec66-657d-570a-278deff0b1a3@iogearbox.net> Date: Thu, 24 Jun 2021 17:06:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <1624507409-114522-1-git-send-email-chengshuyi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.103.2/26211/Thu Jun 24 13:04:24 2021) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/24/21 6:03 AM, 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; > + nit: This should rather go to the 'Parse and load BTF vmlinux if any of [...]' section of struct bpf_object, and for consistency, I'd keep the btf_ prefix, like: char *btf_custom_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); > + } Couldn't we do something like (only compile-tested): diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index b46760b93bb4..5b88ce3e483c 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -4394,7 +4394,7 @@ static int btf_dedup_remap_types(struct btf_dedup *d) * Probe few well-known locations for vmlinux kernel image and try to load BTF * data out of it to use for target BTF. */ -struct btf *libbpf_find_kernel_btf(void) +static struct btf *__libbpf_find_kernel_btf(char *btf_custom_path) { struct { const char *path_fmt; @@ -4402,6 +4402,8 @@ struct btf *libbpf_find_kernel_btf(void) } locations[] = { /* try canonical vmlinux BTF through sysfs first */ { "/sys/kernel/btf/vmlinux", true /* raw BTF */ }, + /* try user defined vmlinux ELF if a path was specified */ + { btf_custom_path }, /* fall back to trying to find vmlinux ELF on disk otherwise */ { "/boot/vmlinux-%1$s" }, { "/lib/modules/%1$s/vmlinux-%1$s" }, @@ -4419,11 +4421,11 @@ struct btf *libbpf_find_kernel_btf(void) uname(&buf); for (i = 0; i < ARRAY_SIZE(locations); i++) { + if (!locations[i].path_fmt) + continue; snprintf(path, PATH_MAX, locations[i].path_fmt, buf.release); - if (access(path, R_OK)) continue; - if (locations[i].raw_btf) btf = btf__parse_raw(path); else @@ -4440,6 +4442,11 @@ struct btf *libbpf_find_kernel_btf(void) return libbpf_err_ptr(-ESRCH); } +struct btf *libbpf_find_kernel_btf(void) +{ + return __libbpf_find_kernel_btf(NULL); +} + int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ctx) { int i, n, err; And then you just call it as: obj->btf_vmlinux = __libbpf_find_kernel_btf(obj->btf_custom_path); err = libbpf_get_error(obj->btf_vmlinux); > 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) { > + 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 * >