From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753260Ab1HVQH3 (ORCPT ); Mon, 22 Aug 2011 12:07:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8481 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752627Ab1HVQH0 (ORCPT ); Mon, 22 Aug 2011 12:07:26 -0400 Date: Mon, 22 Aug 2011 18:07:13 +0200 From: Jiri Olsa To: Eric Dumazet Cc: acme@redhat.com, a.p.zijlstra@chello.nl, mingo@elte.hu, paulus@samba.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] perf, tool, record: Fix the header generation for pipe Message-ID: <20110822160713.GA10134@jolsa.brq.redhat.com> References: <1314022997-9217-1-git-send-email-jolsa@redhat.com> <1314023913.2307.63.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> <20110822145210.GA8694@jolsa.brq.redhat.com> <1314028266.2307.93.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1314028266.2307.93.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> 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 On Mon, Aug 22, 2011 at 05:51:06PM +0200, Eric Dumazet wrote: > Le lundi 22 août 2011 à 16:52 +0200, Jiri Olsa a écrit : > > > - fd is always file.. the descriptor, which might be pipe, is in output_fd variable > > but, maybe the die call is not necessary.. this should not fail > > > > - the record_file function is called only on debugfs or procfs files: > > events/header_page > > events/header_event > > events/**/format > > printk_formats > > /proc/kallsyms > > > > so I think I need to read the whole file as in current code. > > > > You read the file twice. Is it the right fix ? > > Once to compute the length to be able to write the output header, once > to process the content. > > Are you sure length cannot change between the two phases ? > > /proc/kallsyms can definitely change when a module is loaded. Right, better to store it to a temp file as you suggest, so we have consistent view.. I'll prepare new patch. thanks, jirka > > Usually, when input "file" is not seekable or procfs based (fstat() > returns st_size=0), we must load/cache it in memory (or using a > temporary file) to get a consistent view of it. > > This is what is done by following commands : > > cat /proc/kallsyms | less > less /proc/kallsyms > > >