From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: silent semantic changes with reiser4 Date: Thu, 26 Aug 2004 17:19:11 +0100 Message-ID: <20040826161911.GK5733@mail.shareable.org> References: <412CEE38.1080707@namesys.com> <20040825152805.45a1ce64.akpm@osdl.org> <412D9FE6.9050307@namesys.com> <20040826014542.4bfe7cc3.akpm@osdl.org> <1093522729.9004.40.camel@leto.cs.pocnet.net> <20040826124929.GA542@lst.de> <1093525234.9004.55.camel@leto.cs.pocnet.net> <20040826130718.GB820@lst.de> <20040826144422.GD5733@mail.shareable.org> <20040826160306.GA4326@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com To: Christoph Hellwig , Christophe Saout , Andrew Morton , Hans Reiser , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, flx@namesys.com, torvalds@osdl.org, reiserfs-list@namesys.com Content-Disposition: inline In-Reply-To: <20040826160306.GA4326@lst.de> List-Id: linux-fsdevel.vger.kernel.org Christoph Hellwig wrote: > > Unfortunately, the problem is that reiser4 is the only filesystem > > which is _technically capable_ of implementing that abstraction in a > > practical way, apparently. (I'm not sure if this is really true. > > reiser4's object model is not the same as paths and inodes, but the > > impedance mismatch doesn't seem huge.) > > Umm, no. In fact every filesystem does this. There's not too many > objects with different namespace semantic: regular files and special > files vs directories vs symlinks basically, but as soon as you go to the > data patch you can have hundrets of different file_operations on a > single filesystems (for special files). Remember that reiser4 allows you to operate on little pieces of data, glueing and rearranging them inside files (something like that). No other filesystem has that capability, and it's a data model which the fancy features (when they exist) will use. You can map those pieces to underlying directories and files and renames and unlinks, so that the fancy stuff works on other filesystems, but it would be a useless model because those other filesystems wouldn't be recognisably "ordinary" files any more. For reiser4 to expose that model through a VFS interface, and the fancy stuff to use it through the VFS interface, and for the fancy stuff to work (even imperfectly) on other filesystems which don't offer those operations, some kind of fall-back "store metadata and fragment rearrangements in auxiliary files with special names" layer would be requied. That's a big job. I think it's a good job to do (funding, anyone? :), and the right place for that (imperfect but useful) fall-back layer is userspace with perhaps minimal VFS support. Another reason to put the fall-back layer in userspace is that applications which depend on the fancy stuff can still be portable to other OSes, working, but a bit smoother, faster and more "integrated" on reiser4. -- Jamie