From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: [PATCH] ext4: Reserve FEATURE_RO_COMPAT and INO flag Date: Fri, 3 May 2013 02:53:04 -0400 Message-ID: <20130503065304.GB32297@thunk.org> References: <1366900760-18899-1-git-send-email-lczerner@redhat.com> <2B5199BA-39D5-4118-B4FC-96C8B800507B@dilger.ca> <3CAF5E28-8718-4078-ACB9-607CA8DC5BA5@dilger.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: =?utf-8?B?THVrw6HFoQ==?= Czerner , "linux-ext4@vger.kernel.org" To: Andreas Dilger Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:46077 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933378Ab3ECGxI (ORCPT ); Fri, 3 May 2013 02:53:08 -0400 Content-Disposition: inline In-Reply-To: <3CAF5E28-8718-4078-ACB9-607CA8DC5BA5@dilger.ca> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Apr 29, 2013 at 12:35:18PM -0600, Andreas Dilger wrote: > > One real problem that I see is that EXT4_REPLICA_INO uses the > last reserved inode. I recall in the past that Ted wanted to > make this last reserved inode a hidden directory, so that it > would be possible to put special inodes in there and access them > by name. Not quite as easy as accessing a reserved inode by > number, but still preferable to not being able to have filesystem > internal inodes at all in the future. That wasn't my idea, but it's not a bad one. I'm not too worried about running out of file system internal inodes, though. There are two main benefits of having special inode numbers. First, it's a low numbered inode, so it's easy to recognize. Second, it's easier to add a new file system feature to an existing file system. But either way, it's not impossible. First of all, "the first non-reserved inode" is actually a superblock field, so we could actually change that for newer file systems, and hence effectively create new reserved inodes. Secondly, it's simple enough just to use a superblock field to designate a particular inode as being special. This is how we originally dealt with the journal inode, after all. Cheers, - Ted