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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 429FBC432C1 for ; Wed, 25 Sep 2019 10:33:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1CFA4214D9 for ; Wed, 25 Sep 2019 10:33:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389925AbfIYKdx (ORCPT ); Wed, 25 Sep 2019 06:33:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47798 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387892AbfIYKdx (ORCPT ); Wed, 25 Sep 2019 06:33:53 -0400 Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AAC97862E for ; Wed, 25 Sep 2019 10:33:52 +0000 (UTC) Received: by mail-qk1-f199.google.com with SMTP id g65so5048111qkf.19 for ; Wed, 25 Sep 2019 03:33:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=ZZGk1175G8uwjvxdK1U1C4fRiS6VV+Ha9+4WTc5Wkb8=; b=tf2K1ELuc1Mz72M8A3SAzKA8dVDTOQBBWX06/mf2OYQRgXnH5cfybiIoXjZz8mZw7O FSgLwt9XqFBRELnC/Gs62ge6KO+aupGkPC6rdow+OQcUvHkJXEkKCkZJW6ZJy6oiGTmX cEB8SpsagB5MZsTzjkQcPjL+IN9sakFWFrblelnRtBYqcPNeLGrXFAUm9PfxgYzSAmxt BoMNTzWN6fwTzNJ2eDh5yC1CwGbmiOv6i5M459Id7FEoDV0dpXEGecOOcVXbpjSDDDqC fbgJuCZdum9ECuRzW5ARmAH5kgqj2sPuhNtpkgEd3S1PFsZhng8FtkqWVlf8C0MLxYBS +iVw== X-Gm-Message-State: APjAAAWa38nFv3+2FcAvmb2cPz7hBzdg+sICDq1mgZgrMJV5CFlqsdoG J/LfbxO+xgzsc2mNKHhWlPFCGxOfDHDbVz/4Fo+VZAKGwrNrRvL14uhKC/6xYoCpuchWRpV/nfA 3ZA5JLan/zR4c X-Received: by 2002:ac8:16d9:: with SMTP id y25mr7908726qtk.72.1569407632038; Wed, 25 Sep 2019 03:33:52 -0700 (PDT) X-Google-Smtp-Source: APXvYqyx21jj+mlIngD68uZdaLQCpjtwuHMb97xiyJA7Kj8yCO0n3y++SdmxXgWgD4cZyTugtzknMw== X-Received: by 2002:ac8:16d9:: with SMTP id y25mr7908708qtk.72.1569407631903; Wed, 25 Sep 2019 03:33:51 -0700 (PDT) Received: from redhat.com (bzq-79-176-40-226.red.bezeqint.net. [79.176.40.226]) by smtp.gmail.com with ESMTPSA id x59sm2645454qte.20.2019.09.25.03.33.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Sep 2019 03:33:51 -0700 (PDT) Date: Wed, 25 Sep 2019 06:33:43 -0400 From: "Michael S. Tsirkin" To: Matt Cover Cc: davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, Jason Wang , Eric Dumazet , Stanislav Fomichev , Matthew Cover , mail@timurcelik.de, pabeni@redhat.com, Nicolas Dichtel , wangli39@baidu.com, lifei.shirley@bytedance.com, tglx@linutronix.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH net-next] tuntap: Fallback to automq on TUNSETSTEERINGEBPF prog negative return Message-ID: <20190925063142-mutt-send-email-mst@kernel.org> References: <20190920185843.4096-1-matthew.cover@stackpath.com> <20190922080326-mutt-send-email-mst@kernel.org> <20190922162546-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sun, Sep 22, 2019 at 03:46:19PM -0700, Matt Cover wrote: > Unless of course we can simply state via > documentation that any negative return > for which a define doesn't exist is > undefined behavior. In which case, > there is no old vs new behavior and > no need for an ioctl. Simply the > understanding provided by the > documentation. Unfortunately this isn't sufficient: software can easily return a wrong value by mistake, and become dependent on an undefined behaviour. -- MST