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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 F1B13C433FF for ; Tue, 13 Aug 2019 21:56:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB2482067D for ; Tue, 13 Aug 2019 21:56:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726761AbfHMV4U (ORCPT ); Tue, 13 Aug 2019 17:56:20 -0400 Received: from relay8-d.mail.gandi.net ([217.70.183.201]:47889 "EHLO relay8-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726155AbfHMV4U (ORCPT ); Tue, 13 Aug 2019 17:56:20 -0400 X-Originating-IP: 90.65.161.137 Received: from localhost (lfbn-1-1545-137.w90-65.abo.wanadoo.fr [90.65.161.137]) (Authenticated sender: alexandre.belloni@bootlin.com) by relay8-d.mail.gandi.net (Postfix) with ESMTPSA id D4C101BF209; Tue, 13 Aug 2019 21:56:15 +0000 (UTC) Date: Tue, 13 Aug 2019 23:56:15 +0200 From: Alexandre Belloni To: Linus Torvalds Cc: Arnd Bergmann , Linux Kernel Mailing List , Thomas Gleixner , John Stultz , 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? Message-ID: <20190813215615.GE3600@piout.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.0 (2019-05-25) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/08/2019 10:30:34-0700, Linus Torvalds wrote: > On Tue, Aug 13, 2019 at 2:06 AM Arnd Bergmann wrote: > > > > * Should we allow setting the sys_tz on new architectures that use only > > time64 interfaces at all, or should we try to get away from that anyway? > > We should not do TZ on a kernel level at all. At least not a global > one. It makes no sense. > > If the original TZ had been defined to have some sane model (perhaps > per session? Something like that), it would be worth doing. As it is, > a global TZ is just plain wrong. Per process would be sane (but > largely useless, I suspect). > > > * Should the NTP timewarp setting ("int persistent_clock_is_local" and > > its offset) be controllable separately from the timezone used in other > > drivers? > > > > * If we want keep having a way to set the sys_tz, what interface > > should that use? > > I suspect we need to have _some_ way to set the kernel TZ for legacy > reasons, but it should be deprecated and if we can make do without it > entirely on architectures where the legacy doesn't make sense, then > all the better. > > I suspect the only actual _valid_ use in the kernel for a time zone > setting is likely for RTC clock setting, but even that isn't really > "global", as much as "per RTC". > Userspace doesn't need help from the kernel to set the RTC using local time if necessary, this info is in /etc/adjtime and hwclock uses it correctly. It is only needed when the kernel sets the rtc time > That said, if glibc has some sane semantics for TZ, maybe the kernel > can help with that. But 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). I suspect the > kernel can't really do any better. > > Linus -- Alexandre Belloni, Bootlin Embedded Linux and Kernel engineering https://bootlin.com