From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751888Ab0ESFmx (ORCPT ); Wed, 19 May 2010 01:42:53 -0400 Received: from mga11.intel.com ([192.55.52.93]:17622 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751358Ab0ESFmw (ORCPT ); Wed, 19 May 2010 01:42:52 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.53,260,1272870000"; d="scan'208";a="799769490" Subject: Re: [RFC][PATCH v2 08/11] sysfs: introduce new interface sysfs_get_kobject From: Lin Ming To: Greg KH 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 In-Reply-To: <20100519033541.GA25967@kroah.com> References: <1274233723.3036.87.camel@localhost> <20100518200823.GC20223@kroah.com> <1274237717.3603.37.camel@minggr.sh.intel.com> <20100519033541.GA25967@kroah.com> Content-Type: text/plain Date: Wed, 19 May 2010 13:42:00 +0800 Message-Id: <1274247720.3603.91.camel@minggr.sh.intel.com> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 (2.24.1-2.fc10) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-05-19 at 11:35 +0800, Greg KH wrote: > 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? >>From userspace. See "[RFC][PATCH v2 11/11] perf top: demo of how to use the sysfs interfac" for a simple example. > > 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? Yes. > 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)? A simple list of pmus is also added in this patch series There are 2 pmu lookup methods in this patch series. 1. Search a simple list of pmus 2. Lookup pmu via sysfs Method 1 is used for back compatibility. > > 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... Ah, it's that bad... I need to re-think how to export pmus/events to userspace... Lin Ming > > ick. > > greg k-h