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 9D37AC43143 for ; Tue, 2 Oct 2018 12:05:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F564204FD for ; Tue, 2 Oct 2018 12:05:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5F564204FD 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 S1727595AbeJBSs0 (ORCPT ); Tue, 2 Oct 2018 14:48:26 -0400 Received: from mga12.intel.com ([192.55.52.136]:40761 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727510AbeJBSs0 (ORCPT ); Tue, 2 Oct 2018 14:48:26 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Oct 2018 05:05:19 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,331,1534834800"; d="scan'208";a="88485059" Received: from shbuild888.sh.intel.com (HELO localhost) ([10.239.146.239]) by orsmga003.jf.intel.com with ESMTP; 02 Oct 2018 05:05:17 -0700 Date: Tue, 2 Oct 2018 20:10:46 +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: <20181002121046.lsqqnqfu42bazbfx@shbuild888> References: <20180928094008.23138-1-feng.tang@intel.com> <20180929163458.GA25608@zn.tnic> <20180930131619.jecqh4umrkmifavb@shbuild888> <20181001123916.GC7269@zn.tnic> <20181001141810.fbo3amfqnr5243mc@shbuild888> <20181001203004.GG7269@zn.tnic> <20181002091627.3vm6ow4y7me2uju3@shbuild888> <20181002094852.3bw2loje4zjriqe7@shbuild888> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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; Thanks, Feng