Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758914Ab3DYPqz (ORCPT ); Thu, 25 Apr 2013 11:46:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60659 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758557Ab3DYPqy (ORCPT ); Thu, 25 Apr 2013 11:46:54 -0400 Date: Thu, 25 Apr 2013 16:49:55 +0200 From: Jiri Olsa To: Steven Rostedt Cc: Namhyung Kim , Arnaldo Carvalho de Melo , Peter Zijlstra , Paul Mackerras , Ingo Molnar , Namhyung Kim , LKML , Frederic Weisbecker , David Ahern , Stephane Eranian Subject: Re: [PATCH 05/14] perf tools: Introduce new 'ftrace' tool Message-ID: <20130425144955.GC1033@krava.brq.redhat.com> References: <1366705872-12132-1-git-send-email-namhyung@kernel.org> <1366705872-12132-6-git-send-email-namhyung@kernel.org> <20130424140918.GF971@krava.brq.redhat.com> <87fvyf9maa.fsf@sejong.aot.lge.com> <20130425090956.GA1033@krava.brq.redhat.com> <87r4hz7xal.fsf@sejong.aot.lge.com> <1366895121.10248.12.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1366895121.10248.12.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1502 Lines: 48 On Thu, Apr 25, 2013 at 09:05:21AM -0400, Steven Rostedt wrote: > On Thu, 2013-04-25 at 18:51 +0900, Namhyung Kim wrote: > > > > > >> > > >> Do you mean it should be changed to > > >> > > >> if (write_tracing_file("set_ftrace_pid", "-1") < 0) > > >> > > >> ? It seems it's the right thing to do for compatibility. > > > > > > > > > looks like it's enough only to open it with O_TRUNC, > > > so I guess whatever minimal goes write_tracing_file > > Correct. > > > > > Yeah, but I can see below from trace-cmd code. > > > > trace-cmd/trace-record.c: > > > > /* > > * Older kernels required "-1" to disable pid > > */ > > if (ret < 0 && !strlen(pid)) > > ret = write(fd, "-1", 2); > > > > > > Could you clarify this, Steve? > > As the comment states, older kernels (before 2.6.33) required a -1. As > trace-cmd is set up to work with at least 2.6.32, it requires the "-1" > write. It doesn't hurt to have it. > > But for perf ftrace (or whatever), I don't think we need the requirement > to work with 2.6.32 kernels. Perf was added in 2.6.31, but do all > functionalities still work that far back? perf maintains backward compatibility, but not sure how far back it goes.. but as long as it's just writing -1 in here let's do that jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/