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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1DBE9C38A02 for ; Mon, 31 Oct 2022 12:28:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230045AbiJaM2m (ORCPT ); Mon, 31 Oct 2022 08:28:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229576AbiJaM2l (ORCPT ); Mon, 31 Oct 2022 08:28:41 -0400 Received: from mail-qv1-xf2d.google.com (mail-qv1-xf2d.google.com [IPv6:2607:f8b0:4864:20::f2d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 55520233; Mon, 31 Oct 2022 05:28:40 -0700 (PDT) Received: by mail-qv1-xf2d.google.com with SMTP id o8so8218086qvw.5; Mon, 31 Oct 2022 05:28:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:user-agent:references:message-id:date:in-reply-to :subject:cc:to:from:from:to:cc:subject:date:message-id:reply-to; bh=I3bnmf/0ztyUpSdZLRbUrr6EnxUTErY+h3YdktXzr/8=; b=a9eGIp0b/CmTbhtEZWCyaQPTkSivtOLLQCtojRDDy+diYechk5CIpDIc1USa6OcYhn FDTlnoXjk2Fe5xMI/zYCvvxSHJH0HdlIYG/KYhtBjdd9jToPcVxZIiIHRD0vNkAswUPp Df7UzAvgtwVgAL40pSY7jf0dCYgu93j6aPjytPRZWYuyVexFlJzL/LjEc6PEgunv/6xI MqV7CfbKhKYqkMpl5Kc863DSyN3kBcvgdAGd/2UG53ETjUQmSPrDoypG98mCLir6Dise 4sCR1wHXveuguPsha8v7NcMOfD4OX7z5EgOjtNaNt6pjduYYfm5uWYK3W8g6KCsUG0u9 YmWg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=mime-version:user-agent:references:message-id:date:in-reply-to :subject:cc:to:from:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=I3bnmf/0ztyUpSdZLRbUrr6EnxUTErY+h3YdktXzr/8=; b=SkaCS3X/7MlGTU7my6QAaAZVGTxWj0GIzCzdmm683Pk2PTr8w8OLvtNtNh0lug0sYM HUhS/Tihv/d86M40BiGWNQSOA++p/tIQQ17zSts3DgVO3O+L0ZqaH0muO44qT+8gJ61e zUP3MIeRm4w+IfnpByLqmCtukK1OddRjbRt0yU0hJXLQWdJTD3B9VLjc61hx6dyoD6Qg uERpcq18RrjauZDRSaXXOAOw9QNesDS72bgDSfMCeVXT7tOiFKVsqJZb7Ha+eNYlamTC vnF0QHlghUhqatL240cHumHKHciMgmjbdPGCDXK74h2l+Fqstem2syLQDzo8yIaufH4F hNrg== X-Gm-Message-State: ACrzQf1D5jVwP2o/cKPOvcwV9CM+a5KBSDsOmD/iXVP9oD2Xs4v9ZIYv UG8eXdAlZ1cT8vMb+wjYk7pZsLvIjtE= X-Google-Smtp-Source: AMsMyM4EKNXLsZSEcP7h8dsZ8V7uOiuxgGBVarNBKEQULsTwj4YoySnkp+zqwe9+3mskRTbTmNOVew== X-Received: by 2002:a0c:8e89:0:b0:4bb:62a2:b3cb with SMTP id x9-20020a0c8e89000000b004bb62a2b3cbmr10658597qvb.58.1667219319042; Mon, 31 Oct 2022 05:28:39 -0700 (PDT) Received: from imac ([88.97.103.74]) by smtp.gmail.com with ESMTPSA id bs6-20020a05620a470600b006b61b2cb1d2sm4615460qkb.46.2022.10.31.05.28.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Oct 2022 05:28:38 -0700 (PDT) From: Donald Hunter To: John Fastabend Cc: bpf@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH bpf-next v1] Document BPF_MAP_TYPE_LPM_TRIE In-Reply-To: <635c79e315b77_b1ba20836@john.notmuch> (John Fastabend's message of "Fri, 28 Oct 2022 17:54:59 -0700") Date: Mon, 31 Oct 2022 12:28:31 +0000 Message-ID: References: <20221026100232.49181-1-donald.hunter@gmail.com> <635c79e315b77_b1ba20836@john.notmuch> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (darwin) MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org John Fastabend writes: > Donald Hunter wrote: >> + >> +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. > > The map ops lookup, update, delete and below userspace are pretty generic to > all map types. How about moving those into a generic file about maps? Maybe > ./Documentation/bpf/mpas.rst? Then perhaps there is a way to link to > them from here. For the map types I have looked at so far, there has been a bit of variation in semantics. E.g. array has u32 key does not support delete and only supports update with BPF_EXIST/ANY, lpm_trie has custom keys and specific lookup and iteration semantics. Hash has the most generic semantics for get, lookup, update and delete. I am happy to add some generic documentation about the ops in ./Documentation/bpf/maps.rst but I think it will still be necessary to have specific documentation for each map type where the op behaviour deviates. I'd prefer to keep the map specific pages self-contained enough that a reader gets a clear view of behaviour for both kernel BPF and userspace all in one place. >> + >> +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 hash, 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. > > So I tihnk none of this is specific to LPM tries. > >> + >> +Examples >> +======== >> + >> +Please see ``tools/samples/bpf/xdp_router_ipv4_user.c`` and > > I wouldn't link to samples. Can we link to a selftest? Maybe move the > xdp_router_ipv4_user into a selftest otherwise no one ensures it is > always working. I will look for a suitable selftest that I can link to. >> +``xdp_router_ipv4.bpf.c`` for a functional example. The code snippets >> +below demonstrates API usage. >> + >> +Kernel BPF >> +---------- > > rest lgtm. Thanks for working on docs.