From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753189AbZEIPB5 (ORCPT ); Sat, 9 May 2009 11:01:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751766AbZEIPBq (ORCPT ); Sat, 9 May 2009 11:01:46 -0400 Received: from mail-fx0-f158.google.com ([209.85.220.158]:51479 "EHLO mail-fx0-f158.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751410AbZEIPBp convert rfc822-to-8bit (ORCPT ); Sat, 9 May 2009 11:01:45 -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=JIeA16Yp8OCwq3Y4fz5Yde/a/1vcnHwgKTSICzLoDvNZyQgZHtLFvQdt7ft8BzTDnL yCLMC5EIldNoTFTvfW0+Jhab13zD1iIo8ho/8VFkuiegPsAwl81do+z11SUnMx4bvf9E DfVF6N2IE9wRfbthBMn6ir3pD5shXqiVkKAVo= MIME-Version: 1.0 In-Reply-To: <20090509142952.GA3511@Krystal> References: <20090508210347.GA3121@redhat.com> <20090509083737.GE3656@elte.hu> <20090509133306.GA20684@elte.hu> <20090509135046.GA2344@Krystal> <20090509141556.GA24082@elte.hu> <20090509142952.GA3511@Krystal> Date: Sat, 9 May 2009 17:01:44 +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: >> >> > > 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. >> >> There's just a few places (mainly related to VFS APIs) where we >> really want to do that, and there we want to do it a bit later, not >> at syscall time: we want to do it after the getname(), to output a >> stable (and already copied to kernel space) copy of the file name. >> >> So the right solution there would be to add special, case by case >> tracepoints to those few places. We dont need strings for the >> majority of the 300+ system calls that exist on Linux. >> >>       Ingo > > Hrm, this is an important design decision.. I cover a lot of those sites > in my LTTng instrumentation, and this is clearly one way to do it, at > the expense of adding tracepoints in many kernel locations when there > could be a functionnal equivalent with syscall instrumentation. Yeah, these tracepoints defined from DEFINE_SYSCALL are a good way to proceed generically. For specific cases, we can later add some upper layer, such as described below. > The thing we would need to do it from the syscall tracing site is a > table to map the system call numbers to their specific types (for the > syscalls we care about) and therefore which would also map to a > serialisation function to extract the parameters and write the correct > content into the trace buffers. I would rather see this not using the syscalls as a key but the type of a parameter. We can find a same specific complex type used by several syscalls. If we want even better precision, we can also pair that with syscalls mapping for specific post-computing in output time. As an exemple to print O_RDONLY instead of the matching number. > > We could also use getname()/putname() in the syscall tracing primitive. > Note that architectures like x86 64 needs some tweaks I have in my > patchset to correctly ensure that syscall entry/exit are always paired. > This is required because we change the thread flag synchronously with > thread execution upen activation/deactivation. Not sure I understand your point here. The only resulting problem of such race would be rare unpaired syscall exit or entry traces... Is it that much important?