From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754505AbYKFXZl (ORCPT ); Thu, 6 Nov 2008 18:25:41 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752177AbYKFXZc (ORCPT ); Thu, 6 Nov 2008 18:25:32 -0500 Received: from mx2.redhat.com ([66.187.237.31]:52703 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752107AbYKFXZb (ORCPT ); Thu, 6 Nov 2008 18:25:31 -0500 Date: Thu, 6 Nov 2008 18:25:06 -0500 From: "Frank Ch. Eigler" To: Mathieu Desnoyers Cc: Peter Zijlstra , Arjan van de Ven , Steven Rostedt , linux-kernel@vger.kernel.org, mingo@elte.hu, alan@redhat.com, jbaron@redhat.com Subject: Re: [PATCH] ftrace: add an fsync tracer Message-ID: <20081106232506.GF20928@redhat.com> References: <20081106063108.02b4813d@infradead.org> <1225983052.7803.4623.camel@twins> <20081106070157.065b2dcc@infradead.org> <20081106094558.50d94bcc@infradead.org> <1226003343.31966.43.camel@lappy.programming.kicks-ass.net> <20081106215310.GA15163@Krystal> <20081106221426.GD20928@redhat.com> <20081106222529.GA17528@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081106222529.GA17528@Krystal> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi - On Thu, Nov 06, 2008 at 05:25:29PM -0500, Mathieu Desnoyers wrote: > [...] > > Arjan asked for something to send formatted strings to tracing buffers > > that are consumed by user space. Whether internally that is done by > > markers, or by tracepoints converted to markers, or by tracepoints > > with custom ftrace_printf-y code, is indistinguishable to the user. > > > > Can you be specific in what way any of that is exposing an "API > > directly to userspace"? > > The tracepoint declaration is linked to the kernel code that is meant to > be traced. Given this code will change over time, it will be more > difficult to perform those changes if it is in any way coupled with > format strings exported to userspace via traced. [...] The userspace interface to all the various tracing widgets consists of the textual formatted trace data stream. ** IF ** these streams are to represent a long-term interface, can you elaborate why you believe it would be harder to generate identical text in the future with markers rather than another technique with more internal layers? Can you work out an example? (BTW, is "traced" a typo?) And as to that ** IF **: is there actually consensus that the format of tracing data generated by e.g. ftrace engines are supposed to be preserved into the future versions, just as if they were a user-space interface like /proc files? (That's certainly not my impression.) - FChE