Return-Path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:47202 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752526Ab0GVQsf (ORCPT ); Thu, 22 Jul 2010 12:48:35 -0400 In-Reply-To: <20100722162712.GB10352@jeremy-laptop> 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> From: Linus Torvalds Date: Thu, 22 Jul 2010 09:40:22 -0700 Message-ID: Subject: Re: [PATCH 02/18] xstat: Add a pair of system calls to make extended file stats available [ver #6] To: Jeremy Allison Cc: Volker.Lendecke@sernet.de, David Howells , Jan Engelhardt , 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 Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Thu, Jul 22, 2010 at 9:27 AM, Jeremy Allison wrote: > On Thu, Jul 22, 2010 at 08:47:46AM -0700, Linus Torvalds wrote: >> Tell me why we shouldn't just do this right? > > No, ctime isn't the same as Windows "create time". Umm. What kind of reading problems do you guys have? I know effin well that ctime isn't the same as Windows create time. THAT WAS MY POINT. But the fact is, th Unix ctime semantics are insane and largely useless. There's a damn good reason almost nobody uses ctime under unix. So what I'm suggesting is that we have a flag - either per-process or per-mount - that just says "use windows semantics for ctime". And yes, I'm very aware that the "c" in ctime doesn't stand for "create". But anybody who points that out is - once more - totally missing the point. My point is that we have three timestamps, and windows wants three timestamps (somebody claims that NTFS has four timestamps, but the Windows file time access functions certainly only shows three times, so any potential extra on-disk times have no relevance because they are invisible to pretty much everybody). We can have unix semantics for mtime/atime/ctime, or we can have windows semantics for those three values. So let's say that we introduce a mount flag that says "ctime=winctime", which basically just sets a flag that instead of changing ctime on chmod/chown/etc, it just changes mtime instead (or, as mentioned, we could make it a process flag instead). Let's face it, Unix semantics are not sacred. Especially not something like ctime, which is pretty damn useless. If you're a samba server, why not just say "let's do ctime the way windows does creation times", and let it be at that? I personally think that Unix ctime is insane. There is no real reason why "write()" should change mtime, but "chmod" changes ctime. It was just a random decision way back when, and it's clearly not what samba wants, and it's equally clearly not what even most _unix_ people want (just google for "ctime" and "creation time", and watch the confusion - exactly because unix semantics are simply _random_ and odd semantics in this area) I would not be at all surprised if it turns out that people might want to really turn ctime into creation time (with the mount flag or whatever) even if they are _not_ running samba. An added issue is that most filesystems simply don't have more than three times (and some obviously have not even that, but that's true in Windows too). So re-using ctime actually means that this scheme would work a whole lot better than some crazy xstat() interface that doesn't support common filesystems anyway. Linus