From patchwork Tue Nov 1 11:45:42 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Donald Hunter X-Patchwork-Id: 13026910 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 A0FE2FA3743 for ; Tue, 1 Nov 2022 11:50:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231455AbiKALuQ (ORCPT ); Tue, 1 Nov 2022 07:50:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40868 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231334AbiKALtj (ORCPT ); Tue, 1 Nov 2022 07:49:39 -0400 Received: from mail-wr1-x432.google.com (mail-wr1-x432.google.com [IPv6:2a00:1450:4864:20::432]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E23061A238; Tue, 1 Nov 2022 04:45:50 -0700 (PDT) Received: by mail-wr1-x432.google.com with SMTP id h9so19804896wrt.0; Tue, 01 Nov 2022 04:45:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=xgVvXV1TqlbopSpUav8X32PWApDTlkADJpb+ZwiYlZs=; b=o/AwFUfLh1ZseZxhtt/4cXKhcOoE0pxANbWi6XHJLFCkYz0gRTZ5Ca2PlCO4PbsIqR 0k4LVmkTF8xMMSJgH3qESTE7TTfiZw/WbMh+O8uqXjmVTf3LRFWIdTv9e5wR8W5/LHkT GWoOHChf0BUwxtfPxxChj3Vb2gen3rGhpRGbndbbZcIRS79hcTPZhIxsPY0QM+eYbJuX Z3pqD4/eE/szE0vRxx4ZRDYUUCidO+w5GjZvyr5uL0bYN2FzJ4ynG31ES2rnyOtT+E57 olvjY3QJ9CCo1ZI33iyI+UsdaPHjrhaQG6ICAmeDheUGQoehNjdp1YyKXbs5phgU/tEx kEOA== 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=xgVvXV1TqlbopSpUav8X32PWApDTlkADJpb+ZwiYlZs=; b=hxvND7S1OM3gKLIROVfDL/E46jRv9y3AQZZR0RkTcSDB7lPRL32LQIe/1XJpv373GP M/5z4cNrT7hIF9KOl7M5XAXW5y7eMg36/dQaNWtefWY5zh/S9bDtitJcwsNwS8ew4J/E YgfxKsQDqzX4gZMpAKzTYR7eBj5uoSkEG2I7Xrr0AzsKMWwaRIQUFh4M3FIWDLPa6P+J YIUdXmDp2o9MMPfbMdj96LhK8h+Z7H48SijTaoe18rU/Z9G9DRJwygy6d6SWFqPKlbgO QPkOxkh/V0avx2w6uZCt1Jv1ihH8LzMiKuXfGS0imhXzRoJsfo7sS9feTsORBMK8DO2k QJ0A== X-Gm-Message-State: ACrzQf27prUXI6ILzHR9ETBKzudF17H9BRKKtQ1yHdV4akdvvz7M6LOv vlFE9eWkoksdr4Kqi5srL1yJAE9DIO/4nQ== X-Google-Smtp-Source: AMsMyM6TFAcFRaHoCGSQO3O+0lnQzz3aZQ4jdeUJ4jZ53hAAlm0tjAy/NX8n+BNjeVllviQqdIG5Rw== X-Received: by 2002:a5d:5b18:0:b0:236:c174:e99c with SMTP id bx24-20020a5d5b18000000b00236c174e99cmr8085214wrb.10.1667303148905; Tue, 01 Nov 2022 04:45:48 -0700 (PDT) Received: from imac.fritz.box ([2a02:8010:60a0:0:1575:dcd7:a83c:38b]) by smtp.gmail.com with ESMTPSA id f18-20020a1cc912000000b003cf5ec79bf9sm10279291wmb.40.2022.11.01.04.45.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Nov 2022 04:45:48 -0700 (PDT) From: Donald Hunter To: bpf@vger.kernel.org, linux-doc@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jonathan Corbet , Donald Hunter Subject: [PATCH bpf-next v2 1/1] Document BPF_MAP_TYPE_LPM_TRIE Date: Tue, 1 Nov 2022 11:45:42 +0000 Message-Id: <20221101114542.24481-2-donald.hunter@gmail.com> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221101114542.24481-1-donald.hunter@gmail.com> References: <20221101114542.24481-1-donald.hunter@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Add documentation for BPF_MAP_TYPE_LPM_TRIE including kernel BPF helper usage, userspace usage and examples. Signed-off-by: Donald Hunter --- Documentation/bpf/map_lpm_trie.rst | 181 +++++++++++++++++++++++++++++ 1 file changed, 181 insertions(+) create mode 100644 Documentation/bpf/map_lpm_trie.rst diff --git a/Documentation/bpf/map_lpm_trie.rst b/Documentation/bpf/map_lpm_trie.rst new file mode 100644 index 000000000000..31be1aa7ba2c --- /dev/null +++ b/Documentation/bpf/map_lpm_trie.rst @@ -0,0 +1,181 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2022 Red Hat, Inc. + +===================== +BPF_MAP_TYPE_LPM_TRIE +===================== + +.. note:: + - ``BPF_MAP_TYPE_LPM_TRIE`` was introduced in kernel version 4.11 + +``BPF_MAP_TYPE_LPM_TRIE`` provides a longest prefix match algorithm that +can be used to match IP addresses to a stored set of prefixes. +Internally, data is stored in an unbalanced trie of nodes that uses +``prefixlen,data`` pairs as its keys. The ``data`` is interpreted in +network byte order, i.e. big endian, so ``data[0]`` stores the most +significant byte. + +LPM tries may be created with a maximum prefix length that is a multiple +of 8, in the range from 8 to 2048. The key used for lookup and update +operations is a ``struct bpf_lpm_trie_key``, extended by +``max_prefixlen/8`` bytes. + +- For IPv4 addresses the data length is 4 bytes +- For IPv6 addresses the data length is 16 bytes + +The value type stored in the LPM trie can be any user defined type. + +.. note:: + When creating a map of type ``BPF_MAP_TYPE_LPM_TRIE`` you must set the + ``BPF_F_NO_PREALLOC`` flag. + +Usage +===== + +Kernel BPF +---------- + +.. c:function:: + void *bpf_map_lookup_elem(struct bpf_map *map, const void *key) + +The longest prefix entry for a given data value can be found using the +``bpf_map_lookup_elem()`` helper. This helper returns a pointer to the +value associated with the longest matching ``key``, or ``NULL`` if no +entry was found. + +The ``key`` should have ``prefixlen`` set to ``max_prefixlen`` when +performing longest prefix lookups. For example, when searching for the +longest prefix match for an IPv4 address, ``prefixlen`` should be set to +``32``. + +.. c:function:: + long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags) + +Prefix entries can be added or updated using the ``bpf_map_update_elem()`` +helper. This helper replaces existing elements atomically. + +``bpf_map_update_elem()`` returns ``0`` on success, or negative error in +case of failure. + + .. note:: + The flags parameter must be one of BPF_ANY, BPF_NOEXIST or BPF_EXIST, + but the value is ignored, giving BPF_ANY semantics. + +.. c:function:: + long bpf_map_delete_elem(struct bpf_map *map, const void *key) + +Prefix entries can be deleted using the ``bpf_map_delete_elem()`` +helper. This helper will return 0 on success, or negative error in case +of failure. + +Userspace +--------- + +Access from userspace uses libbpf APIs with the same names as above, with +the map identified by ``fd``. + +.. c:function:: + int bpf_map_get_next_key (int fd, const void *cur_key, void *next_key) + +A userspace program can iterate through the entries in an LPM trie using +libbpf's ``bpf_map_get_next_key()`` function. The first key can be +fetched by calling ``bpf_map_get_next_key()`` with ``cur_key`` set to +``NULL``. Subsequent calls will fetch the next key that follows the +current key. ``bpf_map_get_next_key()`` returns ``0`` on success, +``-ENOENT`` if ``cur_key`` is the last key in the trie, or negative +error in case of failure. + +``bpf_map_get_next_key()`` will iterate through the LPM trie elements +from leftmost leaf first. This means that iteration will return more +specific keys before less specific ones. + +Examples +======== + +Please see ``tools/testing/selftests/bpf/test_lpm_map.c`` for examples +of LPM trie usage from userspace. The code snippets below demonstrate +API usage. + +Kernel BPF +---------- + +The following BPF code snippet shows how to declare a new LPM trie for IPv4 +address prefixes: + +.. code-block:: c + + #include + #include + + struct ipv4_lpm_key { + __u32 prefixlen; + __u32 data; + }; + + struct { + __uint(type, BPF_MAP_TYPE_LPM_TRIE); + __type(key, struct ipv4_lpm_key); + __type(value, __u32); + __uint(map_flags, BPF_F_NO_PREALLOC); + __uint(max_entries, 255); + } ipv4_lpm_map SEC(".maps"); + +The following BPF code snippet shows how to lookup by IPv4 address: + +.. code-block:: c + + void *lookup(__u32 ipaddr) + { + struct ipv4_lpm_key key = { + .prefixlen = 32, + .data = ipaddr + }; + + return bpf_map_lookup_elem(&ipv4_lpm_map, &key); + } + +Userspace +--------- + +The following snippet shows how to insert an IPv4 prefix entry into an +LPM trie: + +.. code-block:: c + + int add_prefix_entry(int lpm_fd, __u32 addr, __u32 prefixlen, struct value *value) + { + struct ipv4_lpm_key ipv4_key = { + .prefixlen = prefixlen, + .data = addr + }; + return bpf_map_update_elem(lpm_fd, &ipv4_key, value, BPF_ANY); + } + +The following snippet shows a userspace program walking through the entries +of an LPM trie: + + +.. code-block:: c + + #include + #include + + void iterate_lpm_trie(int map_fd) + { + struct ipv4_lpm_key *cur_key = NULL; + struct ipv4_lpm_key next_key; + struct value value; + int err; + + for (;;) { + err = bpf_map_get_next_key(map_fd, cur_key, &next_key); + if (err) + break; + + bpf_map_lookup_elem(map_fd, &next_key, &value); + + /* Use key and value here */ + + cur_key = &next_key; + } + }