From patchwork Mon Dec 5 22:01:44 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vernet X-Patchwork-Id: 13065116 X-Patchwork-Delegate: bpf@iogearbox.net 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 2597AC4321E for ; Mon, 5 Dec 2022 22:02:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232323AbiLEWCV (ORCPT ); Mon, 5 Dec 2022 17:02:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232490AbiLEWB5 (ORCPT ); Mon, 5 Dec 2022 17:01:57 -0500 Received: from mail-qt1-f169.google.com (mail-qt1-f169.google.com [209.85.160.169]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5D9CA2612; Mon, 5 Dec 2022 14:01:56 -0800 (PST) Received: by mail-qt1-f169.google.com with SMTP id fu10so4025453qtb.0; Mon, 05 Dec 2022 14:01:56 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=ufEai0X98xSIbsVv1GkGx7mHK14NYcBCVwyl1M7ZF5A=; b=MK/ItkuQPb8RLVH7CJVvYOR8KqvNXDTYztejtrxtg4gBuUUDGIiZ6rpbq+GhV0+bcG mQ3aOSWyHHHRV/Buhpenug7FTQb/cgS0ZOVeAG4fIWcNoDLz/owUh+/ZhYe8NxjDKlnY GBX+hcGyS0KdQPAmkXVBwbKQVDaW5nrURn9045U1D9D9UISRggh2rU3pFLf5aH7AoYq4 E5koJlZgXt65ZvLeiz/6DDdgavEHfh+Gdya6HDKq4mWtMqQxf3lubqQiY5rImyuo3W8d /79hYZDNRn5HDY/uleDvyCJo7pz7tQ2xzMonqfR7QpnQ5vP16S78ohDH+XzMbaU/VngL 9fbA== X-Gm-Message-State: ANoB5pmoeycalfeqVL0oqZYTzNqa9CfUk4A6uaDjfYf1GLuhuqFkQ8Kj f+4BpJN4xnSNfRbjybUl8MkoPr8hX8gEElVc X-Google-Smtp-Source: AA0mqf4iYk9DTB78BHYbz1btTx6XFsfTXEBLChBWd1h+ESfc3uHV856UH11JUKxA4Hl+Fy6GUOmLeg== X-Received: by 2002:a05:622a:581a:b0:3a6:59d5:5ec9 with SMTP id fg26-20020a05622a581a00b003a659d55ec9mr55244611qtb.349.1670277715006; Mon, 05 Dec 2022 14:01:55 -0800 (PST) Received: from localhost ([2620:10d:c091:480::1:cc23]) by smtp.gmail.com with ESMTPSA id o6-20020ac85546000000b003a69225c2cdsm8841069qtr.56.2022.12.05.14.01.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Dec 2022 14:01:54 -0800 (PST) From: David Vernet To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@meta.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH bpf-next v2 2/2] bpf/docs: Document struct cgroup * kfuncs Date: Mon, 5 Dec 2022 16:01:44 -0600 Message-Id: <20221205220144.63885-3-void@manifault.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221205220144.63885-1-void@manifault.com> References: <20221205220144.63885-1-void@manifault.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net bpf_cgroup_acquire(), bpf_cgroup_release(), bpf_cgroup_kptr_get(), and bpf_cgroup_ancestor(), are kfuncs that were recnetly added to kernel/bpf/helpers.c. These are "core" kfuncs in that they're available for use in any tracepoint or struct_ops BPF program. Though they have no ABI stability guarantees, we should still document them. This patch adds a struct cgroup * subsection to the Core kfuncs section which describes each of these kfuncs. Signed-off-by: David Vernet --- Documentation/bpf/kfuncs.rst | 49 ++++++++++++++++++++++++++++++++++++ kernel/bpf/helpers.c | 2 +- 2 files changed, 50 insertions(+), 1 deletion(-) diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 59bff92f313c..0eadb28a6ee2 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -370,3 +370,52 @@ Here is an example of it being used: bpf_task_release(lookup); return 0; } + +3.2 struct cgroup * kfuncs +-------------------------- + +``struct cgroup *`` objects also have acquire, release, and kptr_get functions: + +.. kernel-doc:: kernel/bpf/helpers.c + :identifiers: bpf_cgroup_acquire bpf_cgroup_release + +.. kernel-doc:: kernel/bpf/helpers.c + :identifiers: bpf_cgroup_kptr_get + +These kfuncs are used in exactly the same manner as bpf_task_acquire(), +bpf_task_release(), and bpf_task_kptr_get() respectively, so we won't provide +examples for them. + +Another kfunc available for interacting with ``struct cgroup *`` objects is +bpf_cgroup_ancestor(). This allows callers to access the ancestor of a cgroup, +and return it as a cgroup kptr. + +.. kernel-doc:: kernel/bpf/helpers.c + :identifiers: bpf_cgroup_ancestor + +Eventually, BPF should be updated to allow this to happen with a normal memory +load in the program itself. This is currently not possible without more work in +the verifier. bpf_cgroup_ancestor() can be used as follows: + +.. code-block:: c + + /** + * Simple tracepoint example that illustrates how a cgroup's + * ancestor can be accessed using bpf_cgroup_ancestor(). + */ + SEC("tp_btf/cgroup_mkdir") + int BPF_PROG(cgrp_ancestor_example, struct cgroup *cgrp, const char *path) + { + struct cgroup *parent; + + /* The parent cgroup resides at the level before the current cgroup's level. */ + parent = bpf_cgroup_ancestor(cgrp, cgrp->level - 1); + if (!parent) + return -ENOENT; + + bpf_printk("Parent id is %d", parent->self.id); + + /* Return the parent cgroup that was acquired above. */ + bpf_cgroup_release(parent); + return 0; + } diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index a05880f05a78..bc569fce217f 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1940,7 +1940,7 @@ struct cgroup *bpf_cgroup_kptr_get(struct cgroup **cgrpp) } /** - * bpf_cgroup_release - Release the reference acquired on a struct cgroup *. + * bpf_cgroup_release - Release the reference acquired on a struct cgroup kptr. * If this kfunc is invoked in an RCU read region, the cgroup is guaranteed to * not be freed until the current grace period has ended, even if its refcount * drops to 0.