Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751890Ab3CRL1U (ORCPT ); Mon, 18 Mar 2013 07:27:20 -0400 Received: from mail-la0-f44.google.com ([209.85.215.44]:37509 "EHLO mail-la0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751001Ab3CRL1S (ORCPT ); Mon, 18 Mar 2013 07:27:18 -0400 MIME-Version: 1.0 X-Originating-IP: [188.6.195.195] In-Reply-To: <20130314225940.GQ21522@ZenIV.linux.org.uk> References: <1363102908-28956-1-git-send-email-miklos@szeredi.hu> <20130312222350.GK21522@ZenIV.linux.org.uk> <20130313185249.GL21522@ZenIV.linux.org.uk> <20130313231918.GP21522@ZenIV.linux.org.uk> <20130314225940.GQ21522@ZenIV.linux.org.uk> Date: Mon, 18 Mar 2013 12:27:15 +0100 Message-ID: Subject: Re: [PATCH 00/13] overlay filesystem: request for inclusion (v16) From: Miklos Szeredi To: Al Viro Cc: Linus Torvalds , linux-fsdevel , Linux Kernel Mailing List , Christoph Hellwig , Andrew Morton , Robo Bot , Felix Fietkau , Neil Brown , Jordi Pujol , ezk@fsl.cs.sunysb.edu, David Howells , Sedat Dilek , "J. R. Okajima" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1895 Lines: 42 On Thu, Mar 14, 2013 at 11:59 PM, Al Viro wrote: > Huh? > * from st_mode point of view, it's not going to conflict with > anything; FFS "entry type" matches bits 12..15 of mode_t, and the value > picked by whoever had first implemented whiteouts had been chosen so > that it would not clash with any existing values. We have > #define S_IFMT 00170000 > #define S_IFSOCK 0140000 > #define S_IFLNK 0120000 > #define S_IFREG 0100000 > #define S_IFBLK 0060000 > #define S_IFDIR 0040000 > #define S_IFCHR 0020000 > #define S_IFIFO 0010000 > and this sucker would've been 0160000; new filesystem object types are not > frequently introduced, to put it mildly, so I wouldn't expect clashes. I'm worried exactly because new filetypes are introduced so infrequently. No such thing happened during the lifetime of Linux, AFAICT. Backup/restore tools are not going to handle it. File managers are not going to show anything sane (and quite possibly some will simply crash). Yes, all that can be fixed, but it will be a slow and painful process, since union/overlay type filesystems are themselves quite specialized and problems are not going to be shaken out quickly with userspace interaction. On the other hand if a whiteout is exported to userspace as a symlink with xattrs, there will be much less of those problems. BTW I'm not against adding whiteout support to the VFS and possibly to filesystems to clean up the security uglilness and optimize storage. But I think the most important aspect is the userspace interface and I'm far from sure that a new filetype is the best solution here. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/