From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6DA0BC433DF for ; Sun, 16 Aug 2020 23:09:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3EC3D20885 for ; Sun, 16 Aug 2020 23:09:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="B0WGUpCq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726560AbgHPXJW (ORCPT ); Sun, 16 Aug 2020 19:09:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51942 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726288AbgHPXJW (ORCPT ); Sun, 16 Aug 2020 19:09:22 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8274C061786 for ; Sun, 16 Aug 2020 16:09:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=o1yGlNHkaTO6aDYXYPbCQWx9AKxnH13YpSUgTpWcfxo=; b=B0WGUpCqveJJYzoelIQHjacDq0 XKx0eABrRTBsIWYyG9ueA33utUYE1xotAp2d+kHj/cdS15asY9dLpmFEPWDa3GgIl72pLdOdVXFyG ua8P3KeWSTRHNlWGWXWPc5ivPJrVsWs3taf2tgEGEA9mz9cvPHV207xXiOFGxIysVqDVAnowIF/4A wERGxwvOTUlpMIoqk73qdU3sY+2VSbstKd7pj4mSyY1yAW62IMxoSc2z73tLvQr5ECxaJV2dR97Fg KRrHArlKf/Pwk/L1OgN1UIOqor5Lka/D9r2np0o/d/Tob6HGq6UxTax+MfxIB4RBzUZppzmOcoOpL yR+zGyGg==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k7Rm0-0000Xp-My; Sun, 16 Aug 2020 23:09:08 +0000 Date: Mon, 17 Aug 2020 00:09:08 +0100 From: Matthew Wilcox To: Dave Chinner Cc: Christian Schoenebeck , "Dr. David Alan Gilbert" , Greg Kurz , linux-fsdevel@vger.kernel.org, stefanha@redhat.com, mszeredi@redhat.com, vgoyal@redhat.com, gscrivan@redhat.com, dwalsh@redhat.com, chirantan@chromium.org Subject: Re: xattr names for unprivileged stacking? Message-ID: <20200816230908.GI17456@casper.infradead.org> References: <20200728105503.GE2699@work-vm> <12480108.dgM6XvcGr8@silver> <20200812143323.GF2810@work-vm> <27541158.PQPtYaGs59@silver> <20200816225620.GA28218@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200816225620.GA28218@dread.disaster.area> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Aug 17, 2020 at 08:56:20AM +1000, Dave Chinner wrote: > Indeed, most filesystems will not be able to implement ADS as > xattrs. xattrs are implemented as atomicly journalled metadata on > most filesytems, they cannot be used like a seekable file by > userspace at all. If you want ADS to masquerade as an xattr, then > you have to graft the entire file IO path onto filesytsem xattrs, > and that just ain't gonna work without a -lot- of development in > every filesystem that wants to support ADS. > > We've already got a perfectly good presentation layer for user data > files that are accessed by file descriptors (i.e. directories > containing files), so that should be the presentation layer you seek > to extend. > > IOWs, trying to use abuse xattrs for ADS support is a non-starter. One thing Dave didn't mention is that a directory can have xattrs, forks and files (and acls). So your presentation layer needs to not confuse one thing for another. I don't understand why a fork would be permitted to have its own permissions. That makes no sense. Silly Solaris.