From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753536Ab1KOA6h (ORCPT ); Mon, 14 Nov 2011 19:58:37 -0500 Received: from mga14.intel.com ([143.182.124.37]:23556 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751963Ab1KOA6h (ORCPT ); Mon, 14 Nov 2011 19:58:37 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.69,512,1315206000"; d="scan'208";a="74864500" Message-ID: <1321318714.13860.54.camel@yhuang-dev> Subject: Re: Printk mulitple line message support From: Huang Ying To: Bruno =?ISO-8859-1?Q?Pr=E9mont?= Cc: Joe Perches , William Douglas , Andrew Morton , "linux-kernel@vger.kernel.org" Date: Tue, 15 Nov 2011 08:58:34 +0800 In-Reply-To: <20111114192026.73afb5b8@neptune.home> References: <1321253936.13860.35.camel@yhuang-dev> <1321281640.2004.6.camel@Joe-Laptop> <20111114192026.73afb5b8@neptune.home> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.0.3-2 Content-Transfer-Encoding: 8bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2011-11-15 at 02:20 +0800, Bruno Prémont wrote: > On Mon, 14 November 2011 Joe Perches wrote: > > > On Mon, 2011-11-14 at 14:58 +0800, Huang Ying wrote: > > > Hi, > > > > > > In most cases, printk only guarantees messages from different printk > > > calling will not be interleaved between each other. But many printk > > > users uses multiple line to form a complete message and call printk > > > for each line. So the following situation is possible for two printk > > > users running on two CPUs. > > > > > > line 1 of message from printk user1 > > > line 1 of message from printk user2 > > > line 2 of message from printk user1 > > > line 2 of message from printk user2 > > > > > > This makes kernel log hard to read. One possible solution to this > > > issue is to give a sequence number (or ID) to each complete message. > > > So the above lines will be: > > > > > > {1}line 1 of message from printk user1 > > > {2}line 1 of message from printk user2 > > > {1}line 2 of message from printk user1 > > > {2}line 2 of message from printk user2 > > > > > > Then some simple script can be used to group lines together according > > > to sequence number in lines. > > > > > > What do you think about that? > > > > This makes the typical multi-part but non-interleaved > > output difficult to read. > > > > How about determining if there is interleaving and > > emitting sequence # only in those cases? > > > > Perhaps test the atomic for the last sequence #. > > Wouldn't another option be to let printk() handle '\n' in messages > so the multi-line messages could be done with a single call to printk. > > Those messages could contain optional severity information after the > linefeed (if none given, the one of previous line would be repeated > internally by printk). > > This way consumers of printk (and all variations of it like dev_err) > would all benefit without need to redefine them for multi-line use. Yes. That is another solution. But sometimes, it is just not so convenient to do that. The printk users may have to allocate a big buffer to hold all these lines. The solution here is for those users. Best Regards, Huang Ying