From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC 01/32] fs: introduce new 'struct inode_time' Date: Sat, 31 May 2014 16:53:01 +0200 Message-ID: <6491264.Vk0CYaEpvf@wuerfel> References: <1401480116-1973111-1-git-send-email-arnd@arndb.de> <1401480116-1973111-2-git-send-email-arnd@arndb.de> <53899AEA.1010909@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.126.131]:60922 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751588AbaEaOyv (ORCPT ); Sat, 31 May 2014 10:54:51 -0400 In-Reply-To: <53899AEA.1010909@zytor.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: "H. Peter Anvin" Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, joseph@codesourcery.com, john.stultz@linaro.org, hch@infradead.org, tglx@linutronix.de, geert@linux-m68k.org, lftan@altera.com, linux-fsdevel@vger.kernel.org On Saturday 31 May 2014 02:03:38 H. Peter Anvin wrote: > On 05/30/2014 01:01 PM, Arnd Bergmann wrote: > > +#ifdef CONFIG_NEW_INODE_TIME > > +/* > > + * This is the type we use internally in the kernel to represent > > + * absolute times in file system metadata. > > + * This structure must not leak out to user space, and new interfaces > > + * should be using 64-bit types right away. > > + */ > > + > > +/* > > + * Variant a) using unsigned seconds lets us extend the life span > > + * for another 69 years beyond 2038. > > + */ > > +struct inode_time { > > + unsigned long tv_sec; > > + long tv_nsec; > > +}; > > This now differs between 32- and 64-bit systems, and on 32-bit systems > some timestamps well within the range of representation of current > systems just became unrepresentable, which is something that I thought > people were objecting very strongly to. It really depends on the file system. As you pointed out, I was reading the ext2/ext3 and xfs code incorrectly, so my assumption when I wrote this was that they already used the same type, with a 1970-2106 window, rather than the regular signed Unix epoch. > > +#elif 0 > > +/* > > + * This variant can represent the widest range of times, but also > > + * bloats 'struct inode' a little more. > > + */ > > +struct inode_time { > > + long long tv_sec __attribute__((packed)); > > + int tv_nsec; > > +}; > > Seriously, though, can we really impose constraints stricter than what > the filesystems themselves do? It seems we ought to be able to > represent whatever time the filesystem can represent... (modulo some > kind of window control as Y2038 or any other break point approaches.) Just to make sure, do you say we should be using the 'long long/int' struct, or something else? Arnd