From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754729AbZEIOGk (ORCPT ); Sat, 9 May 2009 10:06:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754132AbZEIOGb (ORCPT ); Sat, 9 May 2009 10:06:31 -0400 Received: from mail-fx0-f158.google.com ([209.85.220.158]:40407 "EHLO mail-fx0-f158.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753917AbZEIOGa convert rfc822-to-8bit (ORCPT ); Sat, 9 May 2009 10:06:30 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=KGd2dng3nEkZi5XrDqooVb1rrciMl6FogZ0WjMTNFUgk1t2GS3vIqo4pHTox5fi54E UzxetlCGNtqN37bVB1wp0wquN1rBAJ/u8QNK43fRbSJpCm/N7yrPUS9DcFtQt5H75RlJ ibv2MxgYJH0lFspwPsUto75ODCN3dUueAaY/M= MIME-Version: 1.0 In-Reply-To: <20090509135046.GA2344@Krystal> References: <20090508210347.GA3121@redhat.com> <20090509083737.GE3656@elte.hu> <20090509133306.GA20684@elte.hu> <20090509135046.GA2344@Krystal> Date: Sat, 9 May 2009 16:06:29 +0200 Message-ID: Subject: Re: [RFC] convert ftrace syscall tracer to TRACE_EVENT() From: =?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?= To: Mathieu Desnoyers Cc: Ingo Molnar , Jason Baron , Tom Zanussi , linux-kernel@vger.kernel.org, laijs@cn.fujitsu.com, rostedt@goodmis.org, peterz@infradead.org, jiayingz@google.com, mbligh@google.com, roland@redhat.com, fche@redhat.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2009/5/9 Mathieu Desnoyers : > * Ingo Molnar (mingo@elte.hu) wrote: >> >> * Frédéric Weisbecker wrote: >> >> > > Secondly, we should reuse the information we get in >> > > SYSCALL_DEFINE, to construct the TRACE_EVENT tracepoints >> > > directly - without having to list all syscalls again in a >> > > separate file. >> > >> > Indeed, that's not trivial though, but feasible. I'm not sure we >> > can reuse the TRACE_EVENT macro directly inside SYSCALL_DEFINE. >> > The resulting macro tempest effect that would occur confuses me >> > and I have troubles to imagine the result. >> >> Lets take an example. This syscall: >> >> SYSCALL_DEFINE3(sched_setscheduler, pid_t, pid, int, policy, >>                 struct sched_param __user *, param) >> >> Is equivalent to: >> >> SYSCALL_DEFINE3(name, t1, v1, t2, v2, t3, v3) >> >> ('t' for type, 'v' for variable/value). >> >> This would transform into the following TRACE_EVENT() construct: >> >> TRACE_EVENT_SYSCALL2(): >> >> TRACE_EVENT(sys_##name, >>       TP_PROTO(t1 v1, t2 v2), >>       TP_ARGS(v1, v2), >>       TP_STRUCT__entry( >>               __field(t1, v1) >>               __field(t2, v2) >>       ), >>       TP_fast_assign( >>               __entry->v1 = v1; >>               __entry->v2 = v2; >>       ), >>       TP_printk("%016Lx %016Lx", (u64)__entry->v1, (u64)__entry->v2) >> ); >> >> We need TRACE_EVENT_SYSCALL[123456] definitions, and that's it. >> >> The only place where we lose type information is the printk format - >> but that's not a big issue, as i'd expect the event record to be the >> main user of this. >> >> [ In addition to this, we could extend DEFINE_SYSCALL[1..6] with a >>   (optional) format string definition field, and fill that in for >>   anything that matters. ] >> >> Note, this assumes that all syscall types can be described via >> __field() - i think that's correct. (we dont want to deref strings >> as they are untrusted, and there are no arrays in syscall >> parameters) >> > > I would expect to use copy_string_from_user (for strings) > and copy_from_user for structures, because without any strings > (especially), the trace information become much less useful. Yeah, for structures we would just need the copy_from_user. > This should probably be done at the TP_fast_assign level. > > Note that ftrace fields do not support variable length strings, AFAIK. It does! Look at the __string() field :) > Mathieu > >> Can you see any complication? >> >>       Ingo > > -- > Mathieu Desnoyers > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68 >