From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [GIT PULL] Squashfs pull request for 2.6.29 Date: Sat, 10 Jan 2009 10:12:35 -0800 Message-ID: <20090110101235.7ca24c44.akpm@linux-foundation.org> References: <20090108165029.GA10951@infradead.org> <20090108175338.2abbee16.akpm@linux-foundation.org> <4966B24E.1050700@lougher.demon.co.uk> <20090109023629.GA29520@linuxace.com> <20090109165422.GF24884@logfs.org> <20090109193738.GA9827@linode.davidb.org> <20090109211937.GA14342@logfs.org> <20090110124335.GB30744@elte.hu> <20090110165033.GA23943@logfs.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Ingo Molnar , David Brown , Phil Oester , Kay Sievers , Phillip Lougher , Christoph Hellwig , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org To: =?ISO-8859-1?Q?J=F6rn?= Engel Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:42620 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752127AbZAJSNj (ORCPT ); Sat, 10 Jan 2009 13:13:39 -0500 In-Reply-To: <20090110165033.GA23943@logfs.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sat, 10 Jan 2009 17:50:33 +0100 J__rn Engel wrote: > What is the thing that makes a read only > filesystem special? Nothing, really. The filesystem has mount options (I think). That interface needs to be maintained. More importantly, the filesystem driver has to be able to read older filesystem instances. This is a userspace-visible binary interface! A really complex one. If for some reason we wish to change the on-disk format then that could be done now. But once the code is merged, such changes could only be done in a back-compatible way. And the day-one code (ie: this code) would need to be designed so that such on-disk changes can be made - we don't want old kernels exploding when asked to read new-layout filesystem instances. This is what `grep -i compat include/linux/ext2_fs.h' is all about.