From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 12/15] driver core: Implement tagged directory support for device classes. Date: Wed, 16 Jul 2008 16:02:36 +0900 Message-ID: <487D9D0C.3060105@suse.de> References: <486DD650.3000804@gmail.com> <486E2C3B.6020603@gmail.com> <20080704161200.GA1440@suse.de> <487D6A24.9070001@gmail.com> <487D8C0A.9060100@gmail.com> <487D99C7.708@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Greg KH , Andrew Morton , Daniel Lezcano , linux-kernel@vger.kernel.org, Al Viro , Linux Containers , Benjamin Thery , netdev@vger.kernel.org To: "Eric W. Biederman" Return-path: Received: from ns2.suse.de ([195.135.220.15]:33097 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752034AbYGPHDM (ORCPT ); Wed, 16 Jul 2008 03:03:12 -0400 In-Reply-To: <487D99C7.708@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: Tejun Heo wrote: > Hello, Eric. > > Eric W. Biederman wrote: >> Tejun Heo writes: >> >>> It's a bit scary tho. Working inode->i_dentry or dentry->d_alias >>> crosses multiple sb's. sysfs isn't too greedy about dcache/icache. >>> Only open files and directories hold them and only single copy of >>> sysfs_dirent is there for most nodes. Wouldn't it be better to stay on >>> the safer side and use separate inode hierarchy? >> To do that I believe we would need to ensure sysfs does not use >> the inode->i_mutex lock except to keep the VFS layer out. Allowing us >> to safely change the directory structure, without holding it. > > I don't think sysfs is depending on i_mutex anymore but I need to go > through the code to make sure. > >> You raise a good point about inode->i_dentry and dentry->d_alias. >> Generally they are used by fat like filesystems but I am starting to >> see uses in generic pieces of code. I don't see any problems today >> but yes it would be good to do the refactoring to allow us to duplicate >> the inodes. > > Yeah, I can't spot any place which can cause actual problem yet but it's > still scary as we're breaking a vfs assumption and even if it's not a > problem now, future seemingly unrelated changes can break things subtly. Okay, one small problem spotted. It seems invalidate_inodes() can fail which will make generic_shutdown_super() complain. It's not a fatal failure tho. -- tejun