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 17:00:53 +0100 Message-ID: <20040826160053.GI5733@mail.shareable.org> References: <20040825212518.GK21964@parcelfarce.linux.theplanet.co.uk> <20040826001152.GB23423@mail.shareable.org> <20040826003055.GO21964@parcelfarce.linux.theplanet.co.uk> <20040826010049.GA24731@mail.shareable.org> <412DA40B.5040806@namesys.com> <20040826140500.GA29965@fs.tum.de> <1093530313.11694.56.camel@leto.cs.pocnet.net> <20040826150434.GF5733@mail.shareable.org> <1093533175.11694.77.camel@leto.cs.pocnet.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Adrian Bunk , Hans Reiser , viro@parcelfarce.linux.theplanet.co.uk, Linus Torvalds , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Lyamin aka FLX , ReiserFS List Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com To: Christophe Saout Content-Disposition: inline In-Reply-To: <1093533175.11694.77.camel@leto.cs.pocnet.net> List-Id: linux-fsdevel.vger.kernel.org Christophe Saout wrote: > I'm just thinking about something. While you can't cut bytes out of unix > iles a lot of filesystems can do this (holes). Most of them only on a > block boundary, reiser4 on a byte boundary. If the filesystems could > export this functionality using an enhanced API we could implement a > compression plugin and other things on the VFS level that works with > every filesystem supporting the required mechanisms, not only reiser4. > And those features would take advantage of reiser4's storage mechanisms. > I think Hans made the plugins reiser4-only because only reiser4 has a > similar API at that time (and obviously because he didn't even think > about doing it otherwise). Yes. In some cases the compression or re-archiving algorithm would choose different parameters, depending on the alignment capabilities of the underlying filesystem. In some cases, that alignment is "offset 0 is the only one you can have", which is a severe special case where truncate and rewrite is required for changes. > > By the way, can reiser4 share parts of files between different files? > > At the moment a file is exactly one object. But someone could write > another file plugin that spans a file across multiple objects, then yes, > multiple files could share parts. Nice. That's useful for files which appear as themselves and also as part of a container. And also for revision managed filesystems :) -- Jamie