From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 00/25] Change time_t and clock_t to 64 bit Date: Wed, 14 May 2014 13:00:21 +0200 Message-ID: <8468354.y2kUZdOz9e@wuerfel> References: <1399971456-3941-1-git-send-email-lftan@altera.com> <8399002.IIyBoyEHox@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.17.13]:54193 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754315AbaENLA3 (ORCPT ); Wed, 14 May 2014 07:00:29 -0400 In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Geert Uytterhoeven Cc: Christoph Hellwig , Thomas Gleixner , Ley Foon Tan , Linux-Arch , "linux-kernel@vger.kernel.org" , LeyFoon Tan , Chung-Lin Tang On Tuesday 13 May 2014 22:35:08 Geert Uytterhoeven wrote: > > On Tue, May 13, 2014 at 9:32 PM, Arnd Bergmann wrote: > > I think we have three categories: > > Thanks for the list! > > > a) interfaces that uses relative time_t/timespec/timeval: > > b) interfaces that don't make sense for times in the past: > > > c) interfaces that require absolute times: > > - stat/lstat/fstatat/ > > - utime/utimes/futimesat > > > > These absolutely have to use something better than time_t > > both in user space and in the kernel so we can deal with > > old files. A lot of file systems need to be fixed as well so > > we can actually store the times, regardless of whether we > > are running a 32 or 64 bit kernel. > > So these are the ones we have to worry about. > It looks like they all involve I/O? Apart from the case of using block data > from the buffer cache, the 64-bit operations should disappear in the > actual I/O noise, right? Right. Also there have been proposals for a better 'stat' replacement for years, which would solve half of the interface problem for the file system interfaces. However, we also need to find a solution for category b), I only put them into a different category above because we can treat them differently in the kernel. For instance, we could use ktime_t for the kernel code in category b) and a new struct timespec64 for the times in struct inode. On the user interface side, using timespec64 would be a reasonable choice for both categories, because we already have two implementations of all those syscalls in order to handle 32-on-64 compat tasks, and we could use the same set of syscall implementations for time64-on-32. Arnd