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 15:48:39 +0900 Message-ID: <487D99C7.708@gmail.com> References: <486DD650.3000804@gmail.com> <486E2C3B.6020603@gmail.com> <20080704161200.GA1440@suse.de> <487D6A24.9070001@gmail.com> <487D8C0A.9060100@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 py-out-1112.google.com ([64.233.166.176]:34638 "EHLO py-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751618AbYGPGtN (ORCPT ); Wed, 16 Jul 2008 02:49:13 -0400 Received: by py-out-1112.google.com with SMTP id p76so3280171pyb.10 for ; Tue, 15 Jul 2008 23:49:12 -0700 (PDT) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: 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. Thanks. -- tejun