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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 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 339AFC433EB for ; Wed, 22 Jul 2020 15:25:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 145E620658 for ; Wed, 22 Jul 2020 15:25:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732876AbgGVPZ3 (ORCPT ); Wed, 22 Jul 2020 11:25:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:52592 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728812AbgGVPZ2 (ORCPT ); Wed, 22 Jul 2020 11:25:28 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 08FC4206F5; Wed, 22 Jul 2020 15:25:26 +0000 (UTC) Date: Wed, 22 Jul 2020 11:25:25 -0400 From: Steven Rostedt To: John Ogness Cc: Vincent Whitchurch , jbaron@akamai.com, mingo@redhat.com, kernel@axis.com, corbet@lwn.net, linux-kernel@vger.kernel.org, Petr Mladek , Sergey Senozhatsky Subject: Re: [PATCH] dynamic debug: allow printing to trace event Message-ID: <20200722112525.694880d3@oasis.local.home> In-Reply-To: <87eep3zmg9.fsf@jogness.linutronix.de> References: <20200721141105.16034-1-vincent.whitchurch@axis.com> <20200721173045.540ae500@oasis.local.home> <87eep3zmg9.fsf@jogness.linutronix.de> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Jul 2020 15:58:22 +0206 John Ogness wrote: > >> +static void dynamic_printk(unsigned int flags, const char *fmt, ...) > >> +{ > >> + if (flags & _DPRINTK_FLAGS_TRACE) { > >> + va_list args; > >> + > >> + va_start(args, fmt); > >> + /* > >> + * All callers include the KERN_DEBUG prefix to keep the > >> + * vprintk case simple; strip it out for tracing. > >> + */ > >> + dynamic_trace(fmt + strlen(KERN_DEBUG), args); > > Do we really need a separate tracing event for this? Why not just: > > ftrace_vprintk(fmt + strlen(KERN_DEBUG), args); It must be an event, one that can be enabled or disabled separately from trace_printk(). If you are asking if this could be something like trace_printk(), which ftrace_vprintk() is. The reason for that nasty banner when people use trace_printk() is to keep developers from using it as their personal debugging tool in production. A trace_printk() can not be discretely disabled. It's either totally on, or totally off. And since it is used for debugging, if there's trace_printk()s all over the kernel, you will have to deal with the noise of everyone else's trace_printk(), making trace_printk() useless. Thus, NAK on using ftrace_vprintk() here. -- Steve