Return-Path: Received: from daytona.panasas.com ([67.152.220.89]:28110 "EHLO daytona.int.panasas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752067Ab0GVTxk (ORCPT ); Thu, 22 Jul 2010 15:53:40 -0400 Message-ID: <4C48A1BE.8010503@panasas.com> Date: Thu, 22 Jul 2010 22:53:34 +0300 From: Benny Halevy To: Greg Freemyer CC: Linus Torvalds , Jan Engelhardt , Jeremy Allison , Volker.Lendecke@sernet.de, David Howells , linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org Subject: Re: [PATCH 02/18] xstat: Add a pair of system calls to make extended file stats available [ver #6] References: <20100715021709.5544.64506.stgit@warthog.procyon.org.uk> <20100715021712.5544.44845.stgit@warthog.procyon.org.uk> <30448.1279800887@redhat.com> <20100722162712.GB10352@jeremy-laptop> <4C488C41.60002@panasas.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Jul. 22, 2010, 21:45 +0300, Greg Freemyer wrote: > On Thu, Jul 22, 2010 at 2:21 PM, Benny Halevy wrote: >> On Jul. 22, 2010, 20:24 +0300, Linus Torvalds wrote: >>> On Thu, Jul 22, 2010 at 10:03 AM, Jan Engelhardt wrote: >>>> >>>> I beg to differ. ctime is not completely useless. It reflects changes on >>>> the inode for when you don't you change the content. >>> >>> Uh. Yes. Except that why is file metadata really different from file >>> data? Most people really don't care. And a lot of people have asked >>> for creation dates - and I seriously doubt that Windows people >>> complain a lot about the fact that there you have mtime for metadata >>> changes too. >>> >>> The point being that Unix ctime semantics certainly have well-defined >>> semantics, but they are in no way "better" than having a real creation >>> time, and are often worse. >> >> Yeah, having create time would be important. >> That said, having a non user-settable modify timestamp is crucial >> for quickly determining whether a file has changed. > > How would "cp --archive" and a host of backup/restore tools work > without user-settable modify timestamps? > > Or are you proposing another timestamp? I do computer forensics, I > like timestamps, but enough is enough. mtime and atime are already user settable and archive programs use this on the destination, but ctime would be different after copy/restore. When updating the archive, just comparing mtime to determine if the source changed is problematic as it can be set to any value after the change, but src.ctime would be greater than dest.ctime in this case. With posix semantics (http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap04.html#tag_04_07) this is not perfect either as there can be false-positives when the file stat changed but the file has not, e.g. when st_nlink changed. Benny > > Greg