From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756072Ab0ESDe4 (ORCPT ); Tue, 18 May 2010 23:34:56 -0400 Received: from kroah.org ([198.145.64.141]:34521 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751175Ab0ESDez (ORCPT ); Tue, 18 May 2010 23:34:55 -0400 Date: Tue, 18 May 2010 20:35:41 -0700 From: Greg KH To: Lin Ming Cc: Peter Zijlstra , Ingo Molnar , Corey Ashford , Frederic Weisbecker , Paul Mundt , "eranian@gmail.com" , "Gary.Mohr@Bull.com" , "arjan@linux.intel.com" , "Zhang, Yanmin" , Paul Mackerras , "David S. Miller" , Russell King , Arnaldo Carvalho de Melo , Will Deacon , Maynard Johnson , Carl Love , Kay Sievers , lkml Subject: Re: [RFC][PATCH v2 08/11] sysfs: introduce new interface sysfs_get_kobject Message-ID: <20100519033541.GA25967@kroah.com> References: <1274233723.3036.87.camel@localhost> <20100518200823.GC20223@kroah.com> <1274237717.3603.37.camel@minggr.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1274237717.3603.37.camel@minggr.sh.intel.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 19, 2010 at 10:55:17AM +0800, Lin Ming wrote: > On Wed, 2010-05-19 at 04:08 +0800, Greg KH wrote: > > On Wed, May 19, 2010 at 01:48:43AM +0000, Lin Ming wrote: > > > Need this interface in the later sysfs pmu lookup. > > > > > > struct kobject *sysfs_get_kobject(struct file *file); > > > Return the relative kobject of the sysfs file. > > > > Ick, no. Why would you ever have the file, yet not have the kobject > > already? Something is really wrong if this is needed. Or strange. Or > > maybe both :) > > Let me show you the scenario. > > /sys/devices/system/cpu/event_source/ > `-- id > > /sys/devices/system/cpu/events/ > |-- L1-dcache-load-misses > | |-- event_source -> ../../event_source > > $perf top -e L1-dcache-load-misses > > Lookup the pmu used to handle L1-dcache-load-misses as below, > > 1. pmu_sys_fd = > open("/sys/devices/system/cpu/events/L1-dcache-load-misses/event_source/id", ...) You do that within the kernel? or from userspace? Either way, your id show callback will get called when you read or write to that file, right? Then you have your kobject. > 2. pmu_sys_file = fget_light(pmu_sys_fd, ....) > > 3. pmu_kobject = sysfs_get_kobject(pmu_sys_file) > > 4. pmu_kobject is embedded in struct pmu, pmu = container_of(kobj, > struct pmu, kobj); Oh no. You are just using the kobject sysfs tree to store your kobjects so you can look them up again some time in the future from within the kernel? Seriously? What's wrong with a simple list of kobjects? Or what the rest of the kernel does (busses and devices and iterating over the devices for a bus)? Don't act like userspace here and try to use the sysfs filesystem layout as a lookup into the kobject you are trying to find. That's a horrible abuse of sysfs. One of the worse I have ever seen. And I've seen a lot of sysfs abuse over the years... ick. greg k-h