From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752842AbaCKO1E (ORCPT ); Tue, 11 Mar 2014 10:27:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64575 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752543AbaCKO1C (ORCPT ); Tue, 11 Mar 2014 10:27:02 -0400 Date: Tue, 11 Mar 2014 10:26:50 -0400 From: "Frank Ch. Eigler" To: Steven Rostedt Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, Ingo Molnar , Frederic Weisbecker , Andrew Morton , Johannes Berg Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set via debugfs Message-ID: <20140311142650.GB13756@redhat.com> References: <20140307150920.881849073@goodmis.org> <20140307151202.210588176@goodmis.org> <241011797.35066.1394481694124.JavaMail.zimbra@efficios.com> <20140310225820.0f02025d@gandalf.local.home> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140310225820.0f02025d@gandalf.local.home> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Steven - > > So it is a deferred-activation kind of call, with no way of knowing > > when or if the tracepoints will start coming in. Why is that > > supported at all, considering that clients could monitor modules > > coming & going via the module_notifier chain, and update registration > > at that time? > > That's my argument. Was there an answer? > > >> + entry = get_tracepoint(name); > > >> + /* Make sure the entry was enabled */ > > >> + if (!entry || !entry->enabled) > > >> + ret = -ENODEV; > > > > For what it's worth, I agree with Mathieu that this sort of successful > > failure result code is a problem for tracking what needs cleanup and > > what doesn't. (In systemtap's case, if this change gets merged, we'll > > have to treat -ENODEV as if it were 0.) > > Does systemtap enable tracepoints before they are created? That is, do > you allow enabling of a tracepoint in a module that is not loaded yet? We have no formal opinion on whether or not this makes sense. If the kernel permits it, fine. > If not, than you want this as an error. But it's not exactly an error! It's a success of sorts, and means that later on we have to unregister the callback, just as if it were successful. - FChE