From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27C51C433FF for ; Tue, 13 Aug 2019 19:31:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0519C2054F for ; Tue, 13 Aug 2019 19:31:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726605AbfHMTb3 (ORCPT ); Tue, 13 Aug 2019 15:31:29 -0400 Received: from albireo.enyo.de ([5.158.152.32]:38012 "EHLO albireo.enyo.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726130AbfHMTb3 (ORCPT ); Tue, 13 Aug 2019 15:31:29 -0400 Received: from [172.17.203.2] (helo=deneb.enyo.de) by albireo.enyo.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) id 1hxcVt-0007t6-IB; Tue, 13 Aug 2019 19:31:21 +0000 Received: from fw by deneb.enyo.de with local (Exim 4.92) (envelope-from ) id 1hxcVt-0000qI-DD; Tue, 13 Aug 2019 21:31:21 +0200 From: Florian Weimer To: Paul Eggert Cc: Linus Torvalds , Arnd Bergmann , Linux Kernel Mailing List , Thomas Gleixner , John Stultz , Alexandre Belloni , Stephen Boyd , Florian Weimer , Theodore Ts'o , "H. Peter Anvin" , Palmer Dabbelt , Alistair Francis , GNU C Library , Karel Zak , Lennart Poettering , OGAWA Hirofumi Subject: Re: New kernel interface for sys_tz and timewarp? References: Date: Tue, 13 Aug 2019 21:31:21 +0200 In-Reply-To: (Paul Eggert's message of "Tue, 13 Aug 2019 10:49:03 -0700") Message-ID: <87tvakuak6.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul Eggert: > Linus Torvalds wrote: >> I assume/think that glibc uses (a) environment >> variables and (b) a filesystem-set default (per-user file with a >> system-wide default? I don't know what people do). > glibc relies on the TZ environment variable, with a system-wide > default specified in /etc/localtime or suchlike (there is no > per-user default). glibc ignores the kernel's 'struct timezone' > settings for of this, as 'struct timezone' is obsolete/vestigial and > doesn't contain enough info to do proper conversions anyway. I think the configuration value that settimeofday changes is not actually a time zone, but an time offset used to interpret various things, mostly in a dual-boot environment with Windows, apparently (Like the default time offset for extracting timetamps from FAT volumes.) This data has to come from *somewhere*. The TZ variable and /etc/localtime cover something else entirely. Maybe it is possible to replace these things with other mechanisms which exist today. For example, the mount program could read a configuration file to determine the system default for the time_offset mount option and apply the value automatically. The real-time clock offset could be maintained by whatever mechanism hwclock uses. I think whatever we end up doing, we should maintain consistency after a system upgrade after architectures. It does not make sense to keep using the settimeofday hack on amd64 indefinitely, and switch to a different mechanism on RV32, so that the two ways of supplying the offset are never reconciled across architectures.