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 X-Spam-Level: X-Spam-Status: No, score=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 040DEC433E0 for ; Wed, 20 Jan 2021 15:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CD07723381 for ; Wed, 20 Jan 2021 15:00:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730505AbhATPAg (ORCPT ); Wed, 20 Jan 2021 10:00:36 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46308 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390188AbhATO63 (ORCPT ); Wed, 20 Jan 2021 09:58:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611154623; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fwvMFPt1WboLcOoH23UIfhd2xo9KC7W2tNFuZGnH5tg=; b=LuAN7x0ZV57AWkU+pMrVnXFbb8SjIbUZJvxr1rATfEJ+0q1bB42C3l5P9b7UqObHbuo0wg yXkqxX7xow/cKvAXaNRl12gr4zMMpyfkRHaf8hVcoxCS8thkVM78ezlXKSQ95/M7Nr75a2 Nuk/krXbHiMpvMup1Le62uFSqqJNqmA= Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-144-4nmbKqRMPeOTvGvnFnp7Dg-1; Wed, 20 Jan 2021 09:56:59 -0500 X-MC-Unique: 4nmbKqRMPeOTvGvnFnp7Dg-1 Received: by mail-ed1-f71.google.com with SMTP id g6so11172282edw.13 for ; Wed, 20 Jan 2021 06:56:59 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version:content-transfer-encoding; bh=fwvMFPt1WboLcOoH23UIfhd2xo9KC7W2tNFuZGnH5tg=; b=QwdSUr9x0ETTRHxUuCJfaMmIiXJs8ZANIvegRrAGYDji0HyWoeD78k/xY3lE9KjKpm kX/G+546HyRWrSPO+4/cacZy1Ium/5SkWyg6+a3KSlE2lfpLdXHhIjXVSA42gSMOpLXA mEV//ymd3ClFIz9Ua7zp8qFsDkC545PuFmFWIbD0LdHU+SdvO+Ua0wsz18+m0kOgQelK IB6Y7S0hlH3v85ed3OsGBwK5Bg4EXc2e2Ib8xIZVpNcOTtFqieCpcKWW6VKUZ3lNupVX M4nCNfg9GIBcw1kRDFud2lEvVslh04yIXbBxFr5QFkvalOpUe+DU48osYCfRBQ1smZAJ YMSA== X-Gm-Message-State: AOAM532OJ9CC0kqG4PhU3tz77gNP640RJxZSWWPBneIAFTjM6rXsU3tZ IiPVjV2T6LjxAAjd405hjvWR9fHXUxg1QyvKilw6gF9XbfDmmUWLOzPLUr14Pf2aPYrGv0Ljr6G eaW0aXfAijY4O X-Received: by 2002:aa7:d2d4:: with SMTP id k20mr7518634edr.361.1611154618202; Wed, 20 Jan 2021 06:56:58 -0800 (PST) X-Google-Smtp-Source: ABdhPJy99WUOs30PTEEP3IzAalAndtcfLMV0Alj0wITXpTucPw6kGqbpjitK+lVUsQrpGBXLVfgbTg== X-Received: by 2002:aa7:d2d4:: with SMTP id k20mr7518623edr.361.1611154617989; Wed, 20 Jan 2021 06:56:57 -0800 (PST) Received: from alrua-x1.borgediget.toke.dk ([45.145.92.2]) by smtp.gmail.com with ESMTPSA id w16sm1313993edv.4.2021.01.20.06.56.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Jan 2021 06:56:57 -0800 (PST) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 378D5180331; Wed, 20 Jan 2021 15:56:57 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= , =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= , ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org Cc: magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, kuba@kernel.org, jonathan.lemon@gmail.com, maximmi@nvidia.com, davem@davemloft.net, hawk@kernel.org, john.fastabend@gmail.com, ciara.loftus@intel.com, weqaar.a.janjua@intel.com, Marek Majtyka Subject: Re: [PATCH bpf-next v2 5/8] libbpf, xsk: select AF_XDP BPF program based on kernel version In-Reply-To: <6c7da700-700d-c7f6-fe0a-c42e55e81c8a@intel.com> References: <20210119155013.154808-1-bjorn.topel@gmail.com> <20210119155013.154808-6-bjorn.topel@gmail.com> <875z3repng.fsf@toke.dk> <6c7da700-700d-c7f6-fe0a-c42e55e81c8a@intel.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Wed, 20 Jan 2021 15:56:57 +0100 Message-ID: <87h7nb4pxi.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Bj=C3=B6rn T=C3=B6pel writes: > On 2021-01-20 13:52, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> Bj=C3=B6rn T=C3=B6pel writes: >>=20 >>> From: Bj=C3=B6rn T=C3=B6pel >>> >>> Add detection for kernel version, and adapt the BPF program based on >>> kernel support. This way, users will get the best possible performance >>> from the BPF program. >>=20 >> Please do explicit feature detection instead of relying on the kernel >> version number; some distro kernels are known to have a creative notion >> of their own version, which is not really related to the features they >> actually support (I'm sure you know which one I'm referring to ;)). >> > > Right. For a *new* helper, like bpf_redirect_xsk, we rely on rejection > from the verifier to detect support. What about "bpf_redirect_map() now > supports passing return value as flags"? Any ideas how to do that in a > robust, non-version number-based scheme? Well, having a BPF program pass in a flag of '1' with an invalid lookup and checking if it returns 1 or 0. But how to do that from libbpf, hmm, good question. BPF_PROG_RUN()? An alternative could be to default to a program that will handle both cases in the BPF code, and make it opt-in to use the optimised versions if the user knows their kernel supports it? -Toke