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 14:50:02 +0900 Message-ID: <487D8C0A.9060100@gmail.com> References: <486DD650.3000804@gmail.com> <486E2C3B.6020603@gmail.com> <20080704161200.GA1440@suse.de> <487D6A24.9070001@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 ti-out-0910.google.com ([209.85.142.187]:19473 "EHLO ti-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751090AbYGPFug (ORCPT ); Wed, 16 Jul 2008 01:50:36 -0400 Received: by ti-out-0910.google.com with SMTP id b6so2869690tic.23 for ; Tue, 15 Jul 2008 22:50:33 -0700 (PDT) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: Hello, Eric W. Biederman wrote: >> Eric, with the multiple superblocks, sysfs now uses inode from the >> default sysfs_sb with dentries from other sb's. Is this okay? Are >> there any other filesystems which do this? > > I don't know of any other filesystems where this unique challenge arises. > /proc almost qualifies but it never needs to be modified. > > It is certainly ok to go from multiple dentries to a single inode. > I'm trying to remember why I choose to do that. I think both because it simplifies > the locking and keeps us more efficient in the icache. 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? Thanks. -- tejun