From patchwork Fri Dec 2 22:07:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vernet X-Patchwork-Id: 13063277 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 6C7B1C4321E for ; Fri, 2 Dec 2022 22:07:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234832AbiLBWHr (ORCPT ); Fri, 2 Dec 2022 17:07:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53584 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234523AbiLBWHn (ORCPT ); Fri, 2 Dec 2022 17:07:43 -0500 Received: from mail-qt1-f173.google.com (mail-qt1-f173.google.com [209.85.160.173]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5D360193E8; Fri, 2 Dec 2022 14:07:42 -0800 (PST) Received: by mail-qt1-f173.google.com with SMTP id fp23so6863212qtb.0; Fri, 02 Dec 2022 14:07:42 -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=y0veVtjmL6mXLknvIUK78jBH7zQ0IctC8Qa2dmUAgf4=; b=WleR2rzN4uyveYskwhMjxiduDbEgmd6wqm+UCxNiKtCcT4zEvO1MhZs408C4NTUkw2 AfNSC/obHsSPKIyIQ5qMvpnOEt5NBGCuQzcOzc0USC1iNU2zSmJcoupuGffxGrKwzbc+ lY36hswi/3KC3T5ev91iV8HpLvmJIk4zEQoQjYcKvfZ4JRvbZPq6ImSuMSRAUmNX9JLf 6zoc9D5xCDQxSqGM0t0tTUkno8+WImanqhZOBOHK/AUZ7mBIs7V1G9qehCZGs5dNOk4v jzDZlMn3f0N2YtmPUw3H8JrT0tZ/ioZ6yxHU/W2huxtnW+QsTU5woleBUi6EArQaI+vQ Wt2g== X-Gm-Message-State: ANoB5pnSJQowr+oXnFwGchVi1YGFLoh/jZfDK0zquZKTdB/mwHeNrhwn fC1X4Wtkhb8DD/RM/dJsg519wvnGxj23qng4 X-Google-Smtp-Source: AA0mqf5JbZOB1eXBodyOCKcP5A6YkYl68opaUlTFJzZgTYnHUc4nHL3lezgT77FpAGtx08y/bmtSxA== X-Received: by 2002:ae9:e919:0:b0:6e0:90df:228f with SMTP id x25-20020ae9e919000000b006e090df228fmr47901792qkf.756.1670018861099; Fri, 02 Dec 2022 14:07:41 -0800 (PST) Received: from localhost ([2620:10d:c091:480::1:6d2e]) by smtp.gmail.com with ESMTPSA id n16-20020ac86750000000b003a50248b89esm4855689qtp.26.2022.12.02.14.07.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Dec 2022 14:07:40 -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 2/2] bpf/docs: Document struct cgroup * kfuncs Date: Fri, 2 Dec 2022 16:07:36 -0600 Message-Id: <20221202220736.521227-3-void@manifault.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221202220736.521227-1-void@manifault.com> References: <20221202220736.521227-1-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 b0c35ad6fad4..fd2c8c3b2d52 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -361,3 +361,52 @@ 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 004afbc14bbf..2a07d216c8f3 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1927,7 +1927,7 @@ 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.