From patchwork Tue Dec 6 10:55:52 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Donald Hunter X-Patchwork-Id: 13065668 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 45F9FC4708C for ; Tue, 6 Dec 2022 10:56:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234438AbiLFK4T (ORCPT ); Tue, 6 Dec 2022 05:56:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45778 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234417AbiLFK4S (ORCPT ); Tue, 6 Dec 2022 05:56:18 -0500 Received: from mail-wr1-x435.google.com (mail-wr1-x435.google.com [IPv6:2a00:1450:4864:20::435]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DC897646; Tue, 6 Dec 2022 02:56:17 -0800 (PST) Received: by mail-wr1-x435.google.com with SMTP id q7so22904396wrr.8; Tue, 06 Dec 2022 02:56:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=dVlIS9HqoRWgdQRFba7pm/vsCW9bALpjGInH8aBIHBA=; b=CskNLxD8s+73CC1mfx9c8D3nXRfqWSmuai6glVwbjQfHP4nGjdWj3oiMMY16W2spQv WpfX1ywKRj7d9jbreITzNtC7zk5qUVY96crdjO97GZ70yTZcbRV7i7rREnmz5/rcBLxJ /RISbHYGmzMr1ktzQCs8rANL5vvI+NKGQqJ0nYg6uUg9P8qd0bq87A0Y4fLdvtHFeR8E frOHpUOW13CwBkMv+D51TC/fbXxJGe0X8BVh3fWiGS6AIXqb6hDbnfAaqD9SjCPWcHMg 2hjK/WlZwRRr0Oi8KxNkGajvY4oW1dr6wpKoPO8TkJ39nqaPAnwlvNDJibQHwhFCTiS+ yb9Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=dVlIS9HqoRWgdQRFba7pm/vsCW9bALpjGInH8aBIHBA=; b=WaLiCKDM8BKbJxcS51Yy2IV3hDWQpjPYMC3vVRp5BFW5nr2O56KoDAw/HfgMJHO9zp 4JyD+/BBrM85x7DVgcdy56D1Gnx+pMzycD+wyi2H7sp0Sx0LOtUdAyBJ+ruJtC1Et7Cr AOlLeTDEibvJhBRME2r1XtUcqkqsEQHOwu27jSRfScxvR175zhTKEMSNx4aoBTjI1erZ PxQObOxrvEsY6zzIFb6BCTEn4CR7/0M7SrhuoA4gf5D3At03B3mCmTFunjPeu1/y1LPX Tz73THpxSUDeS6Ckwq1oUVpyyUnrD1pYpxmoOnWW5JLp717RVsLcExbIRKUzpvfIpyDz BtFA== X-Gm-Message-State: ANoB5pn37lZ7+l20cazI6gbZfOBn9QaMVEvrZccTuCKvcvVTM/7wpFR0 141VwelCJudH2U+KC9Q+m6BEeMt/1PvZug== X-Google-Smtp-Source: AA0mqf7jyV+yrsnMNmCtiT26cXnXi2i/lekuy4Aj5Re7IGRjhmmPFgnURj0AuchUaXQGClfYzJX7yg== X-Received: by 2002:a5d:67ca:0:b0:242:7174:c82f with SMTP id n10-20020a5d67ca000000b002427174c82fmr3166399wrw.259.1670324175094; Tue, 06 Dec 2022 02:56:15 -0800 (PST) Received: from imac.fritz.box ([2a02:8010:60a0:0:98f:4f05:72a0:75f0]) by smtp.gmail.com with ESMTPSA id n10-20020adffe0a000000b00241bd7a7165sm15997055wrr.82.2022.12.06.02.56.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Dec 2022 02:56:14 -0800 (PST) From: Donald Hunter To: bpf@vger.kernel.org, linux-doc@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jonathan Corbet , Yonghong Song , Donald Hunter Subject: [PATCH bpf-next v2] docs/bpf: Add documentation for BPF_MAP_TYPE_SK_STORAGE Date: Tue, 6 Dec 2022 10:55:52 +0000 Message-Id: <20221206105552.74372-1-donald.hunter@gmail.com> X-Mailer: git-send-email 2.38.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Add documentation for the BPF_MAP_TYPE_SK_STORAGE including kernel version introduced, usage and examples. Signed-off-by: Donald Hunter --- v1 -> v2: - Fix bpf_sk_storage_* function signatures, reported by Yonghong Song - Fix NULL return on failure, reported by Yonghong Song Documentation/bpf/map_sk_storage.rst | 142 +++++++++++++++++++++++++++ 1 file changed, 142 insertions(+) create mode 100644 Documentation/bpf/map_sk_storage.rst diff --git a/Documentation/bpf/map_sk_storage.rst b/Documentation/bpf/map_sk_storage.rst new file mode 100644 index 000000000000..38b385c53da9 --- /dev/null +++ b/Documentation/bpf/map_sk_storage.rst @@ -0,0 +1,142 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2022 Red Hat, Inc. + +======================= +BPF_MAP_TYPE_SK_STORAGE +======================= + +.. note:: + - ``BPF_MAP_TYPE_SK_STORAGE`` was introduced in kernel version 5.2 + +``BPF_MAP_TYPE_SK_STORAGE`` is used to provide socket-local storage for BPF programs. A map of +type ``BPF_MAP_TYPE_SK_STORAGE`` declares the type of storage to be provided and acts as the +handle for accessing the socket-local storage from a BPF program. The key type must be ``int`` +and ``max_entries`` must be set to ``0``. + +The ``BPF_F_NO_PREALLOC`` must be used when creating a map for socket-local storage. The kernel +is responsible for allocating storage for a socket when requested and for freeing the storage +when either the map or the socket is deleted. + +Usage +===== + +Kernel BPF +---------- + +bpf_sk_storage_get() +~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + long bpf_sk_storage_get(struct bpf_map *map, void *sk, void *value, u64 flags) + +Socket-local storage can be retrieved using the ``bpf_sk_storage_get()`` helper. The helper gets +the storage from ``sk`` that is identified by ``map``. If the +``BPF_LOCAL_STORAGE_GET_F_CREATE`` flag is used then ``bpf_sk_storage_get()`` will create the +storage for ``sk`` if it does not already exist. ``value`` can be used together with +``BPF_LOCAL_STORAGE_GET_F_CREATE`` to initialize the storage value, otherwise it will be zero +initialized. Returns a pointer to the storage on success, or ``NULL`` in case of failure. + +.. note:: + - ``sk`` is a kernel ``struct sock`` pointer for LSM program. + - ``sk`` is a ``struct bpf_sock`` pointer for other program types. + +bpf_sk_storage_delete() +~~~~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + long bpf_sk_storage_delete(struct bpf_map *map, void *sk) + +Socket-local storage can be deleted using the ``bpf_sk_storage_delete()`` helper. The helper +deletes the storage from ``sk`` that is identified by ``map``. Returns ``0`` on success, or negative +error in case of failure. + +User space +---------- + +bpf_map_update_elem() +~~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + int bpf_map_update_elem(int map_fd, const void *key, const void *value, __u64 flags) + +Socket-local storage with type identified by ``map_fd`` for the socket identified by ``key`` can +be added or updated using the ``bpf_map_update_elem()`` libbpf function. ``key`` must be a +pointer to a valid ``fd`` in the user space program. The ``flags`` parameter can be used to +control the update behaviour: + +- ``BPF_ANY`` will create storage for ``fd`` or update existing storage. +- ``BPF_NOEXIST`` will create storage for ``fd`` only if it did not already + exist +- ``BPF_EXIST`` will update existing storage for ``fd`` + +Returns ``0`` on success, or negative error in case of failure. + +bpf_map_lookup_elem() +~~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + int bpf_map_lookup_elem(int map_fd, const void *key, void *value) + +Socket-local storage for the socket identified by ``key`` belonging to ``map_fd`` can be +retrieved using the ``bpf_map_lookup_elem()`` libbpf function. ``key`` must be a pointer to a +valid ``fd`` in the user space program. Returns ``0`` on success, or negative error in case of +failure. + +bpf_map_delete_elem() +~~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + int bpf_map_delete_elem (int map_fd, const void *key) + +Socket-local storage for the socket identified by ``key`` belonging to ``map_fd`` can be deleted +using the ``bpf_map_delete_elem()`` libbpf function. Returns ``0`` on success, or negative error +in case of failure. + +Examples +======== + +Kernel BPF +---------- + +This snippet shows how to declare socket-local storage in a BPF program: + +.. code-block:: c + + struct { + __uint(type, BPF_MAP_TYPE_SK_STORAGE); + __uint(map_flags, BPF_F_NO_PREALLOC); + __type(key, int); + __type(value, struct my_storage); + } socket_storage SEC(".maps"); + +This snippet shows how to retrieve socket-local storage in a BPF program: + +.. code-block:: c + + SEC("sockops") + int _sockops(struct bpf_sock_ops *ctx) + { + struct my_storage *storage; + struct bpf_sock *sk; + + sk = ctx->sk; + if (!sk) + return 1; + + storage = bpf_sk_storage_get(&socket_storage, sk, 0, + BPF_LOCAL_STORAGE_GET_F_CREATE); + if (!storage) + return 1; + + /* Use 'storage' here */ + } + +References +========== + +https://lwn.net/ml/netdev/20190426171103.61892-1-kafai@fb.com/