From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757577AbYEEM3P (ORCPT ); Mon, 5 May 2008 08:29:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753664AbYEEM3A (ORCPT ); Mon, 5 May 2008 08:29:00 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:35047 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752892AbYEEM27 (ORCPT ); Mon, 5 May 2008 08:28:59 -0400 Date: Mon, 5 May 2008 14:28:35 +0200 From: Ingo Molnar To: Mathieu Desnoyers Cc: linux-kernel@vger.kernel.org, systemtap@sources.redhat.com, "Frank Ch. Eigler" Subject: Re: System call instrumentation Message-ID: <20080505122835.GA1523@elte.hu> References: <20080504134838.GA21487@Krystal> <20080505065559.GD3350@elte.hu> <20080505105915.GA26444@Krystal> <20080505111029.GA9948@elte.hu> <20080505113057.GA28070@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080505113057.GA28070@Krystal> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mathieu Desnoyers wrote: > Ideally, I'd like to have this kind of high-level information : > > event name : kernel syscall > syscall name : open > arg1 (%s) : "somefile" <----- > arg2 (%d) : flags > arg3 (%d) : mode > > However, "somefile" has to be read from userspace. With the protection > involved, it would cause a performance impact to read it a second time > rather than tracing the string once it's been copied to kernel-space. performance is a secondary issue here, and copies are fast anyway _if_ someone wants to trace a syscall. (because the first copy brings the cacheline into the cache, subsequent copies are almost for free compared to the first copy) Ingo