Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756327Ab0GVSWA (ORCPT ); Thu, 22 Jul 2010 14:22:00 -0400 Received: from daytona.panasas.com ([67.152.220.89]:51396 "EHLO daytona.int.panasas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755134Ab0GVSV5 (ORCPT ); Thu, 22 Jul 2010 14:21:57 -0400 Message-ID: <4C488C41.60002@panasas.com> Date: Thu, 22 Jul 2010 21:21:53 +0300 From: Benny Halevy User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Linus Torvalds CC: 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> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 22 Jul 2010 18:21:55.0912 (UTC) FILETIME=[C4070C80:01CB29CA] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3263 Lines: 66 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. Benny > > Just imagine what you could do as an MIS person if you actually had a > creation time you could somewhat trust? You talk about seeing somebody > change the permissions of /etc/passwd, but realistically, absent > preexisting semantics, who would really ask for that? The only reason > you mention that as an example of what you can do with ctime is that > that is indeed pretty much the _only_ thing you can do with ctime, and > it really isn't that useful. > > In contrast, with a creation date, you see the difference between > people overwriting files by writing to them, or overwriting files by > creating a new one and moving it over the old one. At a guess, that > would be quite as useful to a sysadmin as ctime is now (my gut feel is > that it would be more so, but whatever). > > IOW, there really isn't anything magically good about UNIX ctime > semantics, and in fact they are totally broken in the presence of > extended attributes (that's file data, but it only changes ctime? WTF > is up with that? Yes, I know why it happens, and it makes sense within > the insane unix ctime rules, but no way does it make sense in a bigger > picture unless you are in total denial and try to claim that xattrs > are just metadata despite having contents). > > And yes, I am also sure that there are applications that do depend on > ctime semantics. Trond mentioned NFS serving, and that's unfortunate. > I bet there are others. That's inevitable when you have 40 years of > history. So I'm not claiming that re-using ctime is painfree, but for > somebody that cares about samba a lot, I bet it's a _lot_ better than > adding a new time that almost nobody actually supports as things stand > now. > > Of people can just use xattrs and do it all entirely in user space. I > assume that's what samba does now, even outside of birthtime. > > Linus > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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/