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 1304CC433EF for ; Wed, 13 Jul 2022 23:30:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229849AbiGMXaS (ORCPT ); Wed, 13 Jul 2022 19:30:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44556 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229735AbiGMXaR (ORCPT ); Wed, 13 Jul 2022 19:30:17 -0400 Received: from mail-pj1-x1049.google.com (mail-pj1-x1049.google.com [IPv6:2607:f8b0:4864:20::1049]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 100F345F7E for ; Wed, 13 Jul 2022 16:30:17 -0700 (PDT) Received: by mail-pj1-x1049.google.com with SMTP id o8-20020a17090ab88800b001ef81869167so2447483pjr.2 for ; Wed, 13 Jul 2022 16:30:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=3tMHBHSEGkpqSv57nbQsmTiS9I+Zeaov4FGtseRBzH0=; b=KzcVs9o6ybHk2CbxYA4wIgX5VUTsOSRfjF6+X6RSEertdAVA/wIJa6ZAZO0s/9pp4q 19Jqkx6eHuVghSUlCl7KbBsUqOW3TvnkyRT5GdcKRyTCNAosBPywdhcCNqWMfpzqIeQs 3VvXHl9DyY6IX9jtfQnrJli1eAJ6A0EzXrQuSgFOtoscbX9badHNn2po02hG15YVbVrw UR7KHyzKibREgkmqjcySQKwYKmhr5eRnPRi7bLEgyiM1wWOZpmHWmO6w8r9xO1FHuPrU spbHga+NlM6Os4+ciVAZ5FT4AJg2qKBdYzFrGHZaKSZcdM6A+MDq9dFgElV69zzdOOQu Ac+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=3tMHBHSEGkpqSv57nbQsmTiS9I+Zeaov4FGtseRBzH0=; b=JYjCjPLKqt0CBrq/Cocr+Qjrbt8PgUBvrQUDJfmpIISKPPnNnK6G/wIzG5RrPS5nk1 7ENE0vVXtTwEOoPV/ifg/nRy7O58+LEsjkXtCQFubhn/9vR2yCsLkXlcIU19I2qSMAsS eI4NdCrXi8oR+dib0bbz1hxrPjn1xHZp7EUXeEWABK2mYhWy0+6dUoTh9xrhqkLygwgI CGfkEtIrY3mAYz7OtD3K0ZDEh+eLrgAuSXBQR9urhvNwIRahgO9N6OeTjoMTIYG+uCdr MWSVH83faKFlIUhbTg4mbgqD6k4+IFM+GIo6gr0ii638Y8j1u9/s91pC5wuwYrZurFUw oPwA== X-Gm-Message-State: AJIora/WFh4Gt2GJZyWcvs9Xcg/avD78WxlO5LSxdNQwRHpRYfn6uzly SC5htOHAgVTM81WTJK2bcmNtFHs= X-Google-Smtp-Source: AGRyM1u+siN+hD3IeWNUBlRzgszyXkIfKl7nhe36zgbNOGMDb6JZqY4vvPICoOl9GulbflaUNPuroK0= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a17:902:8343:b0:167:8899:2f92 with SMTP id z3-20020a170902834300b0016788992f92mr5492603pln.117.1657755016580; Wed, 13 Jul 2022 16:30:16 -0700 (PDT) Date: Wed, 13 Jul 2022 16:30:15 -0700 In-Reply-To: <20220713211612.84782-1-donald.hunter@gmail.com> Message-Id: Mime-Version: 1.0 References: <20220713211612.84782-1-donald.hunter@gmail.com> Subject: Re: [PATCH] bpf, docs: document BPF_MAP_TYPE_HASH and variants From: sdf@google.com To: Donald Hunter Cc: bpf@vger.kernel.org, linux-doc@vger.kernel.org, Jonathan Corbet Content-Type: text/plain; charset="UTF-8"; format=flowed; delsp=yes Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 07/13, Donald Hunter wrote: > This commit adds documentation for BPF_MAP_TYPE_HASH including kernel > version introduced, usage and examples. It also documents > BPF_MAP_TYPE_PERCPU_HASH, BPF_MAP_TYPE_LRU_HASH and > BPF_MAP_TYPE_LRU_PERCPU_HASH which are similar. > Note that this file is included in the BPF documentation by the glob in > Documentation/bpf/maps.rst > Signed-off-by: Donald Hunter > --- > Documentation/bpf/map_hash.rst | 176 +++++++++++++++++++++++++++++++++ > 1 file changed, 176 insertions(+) > create mode 100644 Documentation/bpf/map_hash.rst > diff --git a/Documentation/bpf/map_hash.rst > b/Documentation/bpf/map_hash.rst > new file mode 100644 > index 000000000000..991452e70cc9 > --- /dev/null > +++ b/Documentation/bpf/map_hash.rst > @@ -0,0 +1,176 @@ > +.. SPDX-License-Identifier: GPL-2.0-only > +.. Copyright (C) 2021 Red Hat, Inc. > + > +=============================================== > +BPF_MAP_TYPE_HASH, with PERCPU and LRU Variants > +=============================================== > + > +.. note:: > + - ``BPF_MAP_TYPE_HASH`` was introduced in kernel version 3.19 > + - ``BPF_MAP_TYPE_PERCPU_HASH`` was introduced in version 4.6 > + - Both ``BPF_MAP_TYPE_LRU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH`` > + were introduced in version 4.10 > + > +``BPF_MAP_TYPE_HASH`` and ``BPF_MAP_TYPE_PERCPU_HASH`` provide general > +purpose hash map storage. Both the key and the value can be structs, > +allowing for composite keys and values. The maximum number of entries is > +defined in max_entries and is limited to 2^32. The kernel is responsible Do we really need to mention 2^32 limit here? It really depends on the key/value sizes, right? Instead, might be worth talking about how/when this memory is allocated and mention BPF_F_NO_PREALLOC? > +for allocating and freeing key/value pairs, up to the max_entries limit > +that you specify. ``BPF_MAP_TYPE_PERCPU_HASH`` provides a separate hash > +table per CPU. > + > +Values stored in ``BPF_MAP_TYPE_HASH`` can be accessed concurrently by > +programs running on different CPUs. Since Kernel version 5.1, the BPF > +infrastructure provides ``struct bpf_spin_lock`` to synchronize access. > + > +The ``BPF_MAP_TYPE_LRU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH`` > +variants add LRU semantics to their respective hash tables. An LRU hash > +will automatically evict the least recently used entries when the hash > +table reaches capacity. An LRU hash maintains an internal LRU list that > +is used to select elements for eviction. This internal LRU list is > +shared across CPUs but it is possible to request a per CPU LRU list with > +the ``BPF_F_NO_COMMON_LRU`` flag when calling ``bpf_map_create``. > + > +Usage > +===== > + > +.. c:function:: > + long bpf_map_update_elem(struct bpf_map *map, const void *key, const > void *value, u60 flags) s/u60/u64/ > + > +Hash entries can be added or updated using the ``bpf_map_update_elem()`` > +helper. This helper replaces existing elements atomically. The ``flags`` > +parameter can be used to control the update behaviour: > + > +- ``BPF_ANY`` will create a new element or update an existing element > +- ``BPF_NOTEXIST`` will create a new element only if one did not already > + exist > +- ``BPF_EXIST`` will update an existing element > + > +``bpf_map_update_elem()`` returns 0 on success, or negative error in > +case of failure. > + > +.. c:function:: > + void *bpf_map_lookup_elem(struct bpf_map *map, const void *key) > + > +Hash entries can be retrieved using the ``bpf_map_lookup_elem()`` > +helper. This helper returns a pointer to the value associated with > +``key``, or ``NULL`` if no entry was found. > + > +.. c:function:: > + long bpf_map_delete_elem(struct bpf_map *map, const void *key) > + > +Hash 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. > + > +Per CPU Hashes > +-------------- > + > +For ``BPF_MAP_TYPE_PERCPU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH`` > +the ``bpf_map_update_elem()`` and ``bpf_map_lookup_elem()`` helpers > +automatically access the hash slot for the current CPU. > + > +.. c:function:: > + void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void > *key, u32 cpu) > + > +The ``bpf_map_lookup_percpu_elem()`` helper can be used to lookup the > +value in the hash slot for a specific CPU. Returns value associated with > +``key`` on ``cpu`` , or ``NULL`` if no entry was found or ``cpu`` is > +invalid. > + > +Userspace > +--------- > + > +.. c:function:: > + int bpf_map_get_next_key (int fd, const void *cur_key, void *next_key) > + > +In userspace, is possible to iterate through the keys of a hash using > +the ``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. > + > +Examples > +======== > + > +Please see the ``tools/testing/selftests/bpf`` directory for functional > +examples. This sample code demonstrates API usage. [..] > +Kernel > +------ > + > +.. code-block:: c > + > + #include > + #include > + > + struct key { > + __u32 srcip; > + }; > + > + struct value { > + __u64 packets; > + __u64 bytes; > + }; > + > + struct { > + __uint(type, BPF_MAP_TYPE_LRU_HASH); > + __uint(max_entries, 32); > + __type(key, struct key); > + __type(value, struct value); > + } packet_stats SEC(".maps"); > + > + static inline void count_by_srcip(__u32 srcip, int bytes) > + { > + struct key key = { > + .srcip = srcip > + }; > + struct value *value = bpf_map_lookup_elem(&packet_stats, > &key); > + if (value) { > + __sync_fetch_and_add(&value->packets, 1); > + __sync_fetch_and_add(&value->bytes, bytes); > + } else { > + struct value newval = { 1, bytes }; > + bpf_map_update_elem(&packet_stats, &key, &newval, > BPF_NOEXIST); > + } > + } > + > +Userspace > +--------- > + > +.. code-block:: c > + > + #include > + #include > + > + static void print_values(int map_fd) > + { > + struct key *cur_key = NULL; > + struct key next_key; > + int next; > + do { > + next = bpf_map_get_next_key(stats_fd, cur_key, > &next_key); > + if (next == -ENOENT) > + break; > + if (next < 0) { > + fprintf(stderr, "bpf_map_get_next_key %d > returned %s\n", stats_fd, strerror(-next)); > + break; > + } > + > + struct in_addr src_addr = { > + .s_addr = next_key.srcip > + }; > + char *src_ip = inet_ntoa(src_addr); > + > + struct value value; > + int ret = bpf_map_lookup_elem(stats_fd, &next_key, > &value); > + if (ret < 0) { > + fprintf(stderr, "Failed to lookup elem with > key %s: %s\n", src_ip, strerror(-ret)); > + break; > + } > + printf("%s: %lld packets, %lld bytes\n", src_ip, > value.packets, value.bytes); > + cur_key = &next_key; > + } while (next == 0); > + } Instead of adding c code, maybe add pointers to specific file within tools/testing/selftests/bpf/progs ? That's what we've done for prog_cgroup_sockopt; the actual tests are a bit more maintained than the doc :-)