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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham 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 3381FC43143 for ; Tue, 2 Oct 2018 15:28:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E89A220666 for ; Tue, 2 Oct 2018 15:28:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E89A220666 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727216AbeJBWMf (ORCPT ); Tue, 2 Oct 2018 18:12:35 -0400 Received: from mga03.intel.com ([134.134.136.65]:45098 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726330AbeJBWMf (ORCPT ); Tue, 2 Oct 2018 18:12:35 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Oct 2018 08:28:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,332,1534834800"; d="scan'208";a="79256177" Received: from shbuild888.sh.intel.com (HELO localhost) ([10.239.146.239]) by orsmga006.jf.intel.com with ESMTP; 02 Oct 2018 08:25:40 -0700 Date: Tue, 2 Oct 2018 23:31:10 +0800 From: Feng Tang To: Thomas Gleixner Cc: Borislav Petkov , Ingo Molnar , H Peter Anvin , Peter Zijlstra , "Stuart R . Anderson" , alan@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] x86/earlyprintk: Add a force option for pciserial device Message-ID: <20181002153110.qyttitbdzhtatlev@shbuild888> References: <20180929163458.GA25608@zn.tnic> <20180930131619.jecqh4umrkmifavb@shbuild888> <20181001123916.GC7269@zn.tnic> <20181001141810.fbo3amfqnr5243mc@shbuild888> <20181001203004.GG7269@zn.tnic> <20181002091627.3vm6ow4y7me2uju3@shbuild888> <20181002094852.3bw2loje4zjriqe7@shbuild888> <20181002121046.lsqqnqfu42bazbfx@shbuild888> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181002121046.lsqqnqfu42bazbfx@shbuild888> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 02, 2018 at 08:10:46PM +0800, Feng Tang wrote: > Hi Thomas, > > On Tue, Oct 02, 2018 at 12:44:36PM +0200, Thomas Gleixner wrote: > > On Tue, 2 Oct 2018, Feng Tang wrote: > > > On Tue, Oct 02, 2018 at 11:17:57AM +0200, Thomas Gleixner wrote: > > > > On Tue, 2 Oct 2018, Feng Tang wrote: > > > > > > > > > Hi Boris, > > > > > > > > > > On Mon, Oct 01, 2018 at 10:30:04PM +0200, Borislav Petkov wrote: > > > > > > On Mon, Oct 01, 2018 at 10:18:10PM +0800, Feng Tang wrote: > > > > > > > As I rechecked, the baud rate for pciserial is optional, so there may > > > > > > > be no ",baudrate" following the "force". So this 2 strncmp is to > > > > > > > cover conditions for with and without baudrate. > > > > > > > > > > > > And what guarantees you have a space after the "force"? > > > > > > > > > > > > !strncmp(s, "force ", 6) > > > > > > ^ > > > > > > > > > > You are right, it can't be guranteed. Can we still use strncmp(s, "force", 5) > > > > > and rely on developer to set it right? any suggestions? thanks, > > > > > > > > I don't know why you want strncmp() in the first place. "force" is null > > > > terminated already. > > > > > > Current code uses: > > > earlyprintk=pciserial,bus:device.function[,baudrate] > > > with the patch, it will be: > > > earlyprintk=pciserial,bus:device.function[,force][,baudrate] > > > > > > So the force could be followed by ",baudrate". > > > > Sure, but that has nothing to do with strncmp(). The earlyprintk argument > > string is tokenized by commata. It really does not matter where the 'force' > > string is, but it matters that you check whether it is 'force' and not > > 'force$RANDOMCHARACTERS'. That's why strncmp() is the wrong thing to do, > > because it only compares the first 5 characters and ignores anything > > beyond, unless you make sure that the command line part is exactly 5 > > characters long. > > I don't know if I get it right due to my poor English, so for both cases > of "xxx,force,baudrate" and "xxx,force", it could be covered by > > if ((!strcmp(s, "force") || !strncmp(s, "force," 6)) > force = 1; One idea is to change the new format to earlyprintk=pciserial[,force],bus:device.function[,baudrate] Then we can use what Boris has suggested: !strncmp(s, "force,", 6) Any thoughts? Thanks, Feng