From patchwork Mon Nov 21 14:22:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Maryam Tahhan X-Patchwork-Id: 13051078 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 0F2A4C4332F for ; Mon, 21 Nov 2022 14:24:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231418AbiKUOYf (ORCPT ); Mon, 21 Nov 2022 09:24:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35112 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230480AbiKUOXt (ORCPT ); Mon, 21 Nov 2022 09:23:49 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9FC1642A for ; Mon, 21 Nov 2022 06:22:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669040569; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Mt/4kG5u+q4960OnggQxBF4VwJ0IyUcVyeLIY1/apXs=; b=cbgbhUF2WfrAyTd68o2ryIXk6oV8GdteGoEV+AXwee2qOunOEM8bKm9qjBPRyeH+kV79nx C3DdYVIK0+LSg1MTuAikIzf5p6rdrXWFPdPXwgz4756R98GlReM4qM5R5rjK2hxAqZeVN4 ZzM7sFhTIp9hPuUMvUv22STpxAyZa8g= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-644-E2mpLLHRPTugGBWgdxfVCw-1; Mon, 21 Nov 2022 09:22:48 -0500 X-MC-Unique: E2mpLLHRPTugGBWgdxfVCw-1 Received: by mail-wr1-f70.google.com with SMTP id s11-20020adfbc0b000000b0023659af24a8so3311292wrg.14 for ; Mon, 21 Nov 2022 06:22:47 -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:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=Mt/4kG5u+q4960OnggQxBF4VwJ0IyUcVyeLIY1/apXs=; b=mzEzECxJHQi/E7NQYkM/4cD4X9lTizu040Zll0lgbAKtsArTFdTZWdYYW/WpaC/nQd HPHgdY0epjJpz/toCXpunDYhQ1qFlf20+CAHVGCkOj1OjsxtGfNaKUJ9g7fXhcfSkaWj gKXN4B6cZdU4g1mEQRGn1QNnDLIiCzFndiijORAIqPyVpO06NyGLIa/x4Radhi1SsZkB 73eMYeQ+HZgjyDbBPFiUYTgOtn7EbuQYt1vmGvoHOqSP02bMZzLvFTZz2l7Z3IS9FHEU GY12JXhF+fR3mSYPM0gt3VVXPz+uYhiPu77kjXixKuP5LNvqru2WVzxk4GR2e6EA+xD0 b0Fw== X-Gm-Message-State: ANoB5pnpm3UBsZcHNU58OzyBFUvEzDBU1XDEk4SNmJ4xP2HEaefM7Ni6 N25EVvOYL30RGxnKyHfIf6GJ+yrHfHdN1GUDd85NNVx+nHVC0rQ2UHTr4rzvJEmX5o0IWMOSABW P0JySno5Dt3KQRcuXCkuXVXsDvZGKndEzXj6WqRyC0hOoYPQ1Ciw1vvOGfTaACxs= X-Received: by 2002:a05:6000:1107:b0:241:7e9f:8afd with SMTP id z7-20020a056000110700b002417e9f8afdmr10729108wrw.228.1669040565753; Mon, 21 Nov 2022 06:22:45 -0800 (PST) X-Google-Smtp-Source: AA0mqf7R+Jzyu/C3zQr7x2WM7RqaRKzuhQfg0A1yIfohGwllv722tp2HcGvXS1b+IJ8ixClmDL9Ouw== X-Received: by 2002:a05:6000:1107:b0:241:7e9f:8afd with SMTP id z7-20020a056000110700b002417e9f8afdmr10729090wrw.228.1669040565421; Mon, 21 Nov 2022 06:22:45 -0800 (PST) Received: from teaching-eagle.redhat.com ([78.19.107.254]) by smtp.gmail.com with ESMTPSA id c2-20020a05600c0a4200b003cfd4cf0761sm20212480wmq.1.2022.11.21.06.22.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Nov 2022 06:22:44 -0800 (PST) From: mtahhan@redhat.com To: bpf@vger.kernel.org, linux-doc@vger.kernel.org Cc: jbrouer@redhat.com, thoiland@redhat.com, donhunte@redhat.com, magnus.karlsson@gmail.com, akiyks@gmail.com, Maryam Tahhan Subject: [PATCH bpf-next v3 1/1] docs: BPF_MAP_TYPE_XSKMAP Date: Mon, 21 Nov 2022 14:22:40 +0000 Message-Id: <20221121142240.40451-1-mtahhan@redhat.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net From: Maryam Tahhan Add documentation for BPF_MAP_TYPE_XSKMAP including kernel version introduced, usage and examples. Signed-off-by: Maryam Tahhan --- v3: - Fixed duplicate function warnings from Sphinx >= 3.3. v2: - Fixed typos + incorrect return type references. - Adjusted examples to use __u32 and fixed references to key_size. - Changed `AF_XDP socket` references to XSK. - Added note re map key and value size. --- Documentation/bpf/map_xskmap.rst | 173 +++++++++++++++++++++++++++++++ 1 file changed, 173 insertions(+) create mode 100644 Documentation/bpf/map_xskmap.rst diff --git a/Documentation/bpf/map_xskmap.rst b/Documentation/bpf/map_xskmap.rst new file mode 100644 index 000000000000..8715034600d4 --- /dev/null +++ b/Documentation/bpf/map_xskmap.rst @@ -0,0 +1,173 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2022 Red Hat, Inc. + +=================== +BPF_MAP_TYPE_XSKMAP +=================== + +.. note:: + - ``BPF_MAP_TYPE_XSKMAP`` was introduced in kernel version 4.18 + +The ``BPF_MAP_TYPE_XSKMAP`` is used as a backend map for XDP BPF helper +call ``bpf_redirect_map()`` and ``XDP_REDIRECT`` action, like 'devmap' and 'cpumap'. +This map type redirects raw XDP frames to AF_XDP sockets (XSKs). An AF_XDP socket +binds to a single netdev queue. A mapping of XSKs to queues is shown below: + +.. code-block:: none + + +---------------------------------------------------+ + | xsk A | xsk B | xsk C |<---+ Userspace + =========================================================|========== + | Queue 0 | Queue 1 | Queue 2 | | Kernel + +---------------------------------------------------+ | + | Netdev eth0 | | + +---------------------------------------------------+ | + | +=============+ | | + | | key | xsk | | | + | +---------+ +=============+ | | + | | | | 0 | xsk A | | | + | | | +-------------+ | | + | | | | 1 | xsk B | | | + | | eBPF |-- redirect -->+-------------+-------------+ + | | prog | | 2 | xsk C | | + | | | +-------------+ | + | | | | + | | | | + | +---------+ | + | | + +---------------------------------------------------+ + +.. note:: + An AF_XDP socket that is bound to a certain will *only* + accept XDP frames from that . If an XDP program tries to redirect + from a other than what the socket is bound to, the frame will + not be received on the socket. + +Typically a XSKMAP is created per netdev. This map contains an array of XSK File +Descriptors (FDs). The number of array elements is typically set or adjusted using +the ``max_entries`` map parameter. For AF_XDP ``max_entries`` is equal to the number +of queues supported by the netdev. + +.. note:: + Both the map key and map value size must be 4 bytes. + +Usage +===== + +Kernel BPF +---------- + +.. code-block:: c + + long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags) + +Redirect the packet to the endpoint referenced by ``map`` at index ``key``. +For ``BPF_MAP_TYPE_XSKMAP`` this map contains references to XSK FDs +for sockets attached to a netdev's queues. + +.. note:: + If the map is empty at an index, the packet is dropped. This means that it is + necessary to have an XDP program loaded with at least one XSK in the + XSKMAP to be able to get any traffic to user space through the socket. + +.. code-block:: c + + void *bpf_map_lookup_elem(struct bpf_map *map, const void *key) + +XSK entry references of type ``struct xdp_sock *`` can be retrieved using the +``bpf_map_lookup_elem()`` helper. + +Userspace +--------- +.. note:: + XSK entries can only be updated/deleted from user space and not from + an eBPF program. Trying to call these functions from a kernel eBPF program will + result in the program failing to load and a verifier warning. + +.. code-block:: c + + int bpf_map_update_elem(int fd, const void *key, const void *value, __u64 flags) + +XSK entries can be added or updated using the ``bpf_map_update_elem()`` +helper. The ``key`` parameter is equal to the queue_id of the queue the XSK +is attaching to. And the ``value`` parameter is the FD value of that socket. + +Under the hood, the XSKMAP update function uses the XSK FD value to retrieve the +associated ``struct xdp_sock`` instance. + +The flags argument can be one of the following: + +- BPF_ANY: Create a new element or update an existing element. +- BPF_NOEXIST: Create a new element only if it did not exist. +- BPF_EXIST: Update an existing element. + +.. code-block:: c + + int bpf_map_lookup_elem(int fd, const void *key, void *value) + +Returns ``struct xdp_sock *`` or negative error in case of failure. + +.. code-block:: c + + int bpf_map_delete_elem(int fd, const void *key) + +XSK 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. + +.. note:: + When `libxdp`_ deletes a XSK it also removes the associated socket + entry from the XSKMAP. + +Examples +======== +Kernel +------ + +The following code snippet shows how to declare a ``BPF_MAP_TYPE_XSKMAP`` called +``xsks_map`` and how to redirect packets to a XSK. + +.. code-block:: c + + struct { + __uint(type, BPF_MAP_TYPE_XSKMAP); + __type(key, __u32); + __type(value, __u32); + __uint(max_entries, 64); + } xsks_map SEC(".maps"); + + + SEC("xdp") + int xsk_redir_prog(struct xdp_md *ctx) + { + __u32 index = ctx->rx_queue_index; + + if (bpf_map_lookup_elem(&xsks_map, &index)) + return bpf_redirect_map(&xsks_map, index, 0); + return XDP_PASS; + } + +Userspace +--------- + +The following code snippet shows how to update a XSKMAP with a XSK entry. + +.. code-block:: c + + int update_xsks_map(struct bpf_map *xsks_map, int queue_id, int xsk_fd) + { + int ret; + + ret = bpf_map_update_elem(bpf_map__fd(xsks_map), &queue_id, &xsk_fd, 0); + if (ret < 0) { + fprintf(stderr, "Failed to update xsks_map: %s\n", + strerror(errno)); + } + + return ret; + } + +.. note:: + The most comprehensive resource for using XSKMAPs is `libxdp`_. + +.. _libxdp: https://github.com/xdp-project/xdp-tools/tree/master/lib/libxdp