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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 23FA0C433E1 for ; Mon, 10 Aug 2020 07:32:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0252220774 for ; Mon, 10 Aug 2020 07:32:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="J526to2D" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726584AbgHJHcY (ORCPT ); Mon, 10 Aug 2020 03:32:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726569AbgHJHcX (ORCPT ); Mon, 10 Aug 2020 03:32:23 -0400 Received: from mail-vs1-xe41.google.com (mail-vs1-xe41.google.com [IPv6:2607:f8b0:4864:20::e41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27FCAC061756 for ; Mon, 10 Aug 2020 00:32:23 -0700 (PDT) Received: by mail-vs1-xe41.google.com with SMTP id q13so3730782vsn.9 for ; Mon, 10 Aug 2020 00:32:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=sJo6TZcaNoJonrq3wQzaYlOn0q7KCaKbS7KLCKU2QzA=; b=J526to2DvxuRZ8736kFIZtIMrd+wGpUCmG9v/rejtCm6ZNbh/i5xF906ohsgmAiJ78 FPeEcYbsYrJ3+Qiyi7vfxUQIT0YTtEeGabjI+phjc6DvfO3d/No2a/62W+3KjbK9N1yE C8EIRoSvnU2dzVpWyvin8SRVuszcz2foFihxhvFK6OQYA/F+eJS2pfM1+0cTYy/Z4bn3 SKofNlcHWdAd0oGfiCt5GOYGUbIDXX+ZVEcHaE/xSSqEV02cBBNtLQs86tNIL+zkUeut lIqtPEQSc3Ru8im6pH2QAvwoxYV0EO8jBYG12kwkquzTCdgHQqKnVDF9bVWjNAizum9R S8Ug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=sJo6TZcaNoJonrq3wQzaYlOn0q7KCaKbS7KLCKU2QzA=; b=CI17sER/iWy1TbXVelfUHLVR3SyEgHV19nVpKEO2BCAbaSqLP9vqczkWqpZrGFrXc7 ykNUKUzKJwRIKKwaDTqn54UbUvzTa7Ovf5E6gR+Gigzwr56VViyYad5f1y689UDt/0qp KU6NOLEa7sQN1+BxaWNjTtaBjQ11/cpGX6aLKSbaC0W+KmMwpTOUpbyjMMfTok36Z5PW c5VXbCrqg6iK3ULktcnOvZpOe2IFNoxQWgkRQ5PG+L3YOfFqoIoY2+I7/q52R8sUSRn5 UPus773cD+LsTeesW+JCF9AqJuy9hfLN49Zo60r+bqmpESCLwADuTcRsYWEgpBdT3n4G WULw== X-Gm-Message-State: AOAM5315ac8kdjngTW8e74lIx5WK5ghtijqiKyoXegUxdq8Ki5H9pm6y 3u4hJ+VENnQTGLToaOCYKi5NHoiRr0M= X-Google-Smtp-Source: ABdhPJwfj+lqh5UXN4yGfQF1OOn+Td5tS9D3+s3eMOXPR63VH0UhOblIf7+hRiDVTVMGyJ8JX5JuIQ== X-Received: by 2002:a67:1a43:: with SMTP id a64mr18715365vsa.235.1597044741713; Mon, 10 Aug 2020 00:32:21 -0700 (PDT) Received: from mail-ua1-f45.google.com (mail-ua1-f45.google.com. [209.85.222.45]) by smtp.gmail.com with ESMTPSA id d27sm1659121vkl.43.2020.08.10.00.32.20 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Aug 2020 00:32:20 -0700 (PDT) Received: by mail-ua1-f45.google.com with SMTP id g20so1242607uap.8 for ; Mon, 10 Aug 2020 00:32:20 -0700 (PDT) X-Received: by 2002:a9f:2648:: with SMTP id 66mr13443939uag.37.1597044739732; Mon, 10 Aug 2020 00:32:19 -0700 (PDT) MIME-Version: 1.0 References: <20200808175251.582781-1-xie.he.0141@gmail.com> In-Reply-To: From: Willem de Bruijn Date: Mon, 10 Aug 2020 09:31:43 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH net] drivers/net/wan/lapbether: Added needed_tailroom To: Xie He Cc: "David S. Miller" , Jakub Kicinski , Network Development , linux-kernel , Linux X25 , Martin Schiller Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sun, Aug 9, 2020 at 7:12 PM Xie He wrote: > > On Sun, Aug 9, 2020 at 1:48 AM Willem de Bruijn > wrote: > > > > Does this solve an actual observed bug? > > > > In many ways lapbeth is similar to tunnel devices. This is not common. > > Thank you for your comment! > > This doesn't solve a bug observed by me. But I think this should be > necessary considering the logic of the code. > > Using "grep", I found that there were indeed Ethernet drivers that set > needed_tailroom. I found it was set in these files: > drivers/net/ethernet/sun/sunvnet.c > drivers/net/ethernet/sun/ldmvsw.c > Setting needed_tailroom may be necessary for this driver to run those > Ethernet devices. What happens when a tunnel device passes a packet to these devices? That will also not have allocated the extra tailroom. Does that cause a bug?