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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 99D33C433FF for ; Wed, 14 Aug 2019 16:48:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 67F0B2084F for ; Wed, 14 Aug 2019 16:48:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="afIXOvzQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728387AbfHNQsm (ORCPT ); Wed, 14 Aug 2019 12:48:42 -0400 Received: from terminus.zytor.com ([198.137.202.136]:52443 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726722AbfHNQsl (ORCPT ); Wed, 14 Aug 2019 12:48:41 -0400 Received: from [IPv6:2601:646:8600:3281:2c7e:a77e:9d52:7c32] ([IPv6:2601:646:8600:3281:2c7e:a77e:9d52:7c32]) (authenticated bits=0) by mail.zytor.com (8.15.2/8.15.2) with ESMTPSA id x7EGllrZ1907212 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO); Wed, 14 Aug 2019 09:48:01 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com x7EGllrZ1907212 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2019071901; t=1565801283; bh=etksQiyq83kHLcBsVn7h/6r7t63sqJ6ZCqfbAq4s+jQ=; h=Date:In-Reply-To:References:Subject:To:CC:From:From; b=afIXOvzQgx2qnlUply+r6xDQ/x1UoaNoAc80t7FMe+ADbLOY7B8I85FxiGS41ewHv XmobnrMVZGAAOAA3+CPcfoYqjFCiyF12rgTiNgGTPXUzSphHqYR6CTpRqGWOIU3cd8 UURdgkI8mNPSrEfi+nZX3zyWtIQN54jdfFuhB815yqvTII0/8x1LHJr3II4E66gd2H roKmSp76TUtmYxRgrGhE00kpjNpi7nkr2LDk9hUoMrlZ1mu3JjPn8mh+vMdqRrUrMp MPIxtDTWgs8tbCZhQqpmOrRUxobIU3xJCQ51x3zAJFnEPq5/L/cvQ/aWq8h6BBoMtJ /DxyLVXZZju5g== Date: Wed, 14 Aug 2019 09:47:39 -0700 User-Agent: K-9 Mail for Android In-Reply-To: <342565604d704b6ebaf2e9ec28d3e109@AcuMS.aculab.com> References: <20190814000622.GB20365@mit.edu> <342565604d704b6ebaf2e9ec28d3e109@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: RE: New kernel interface for sys_tz and timewarp? To: David Laight , "'Theodore Y. Ts'o'" , Linus Torvalds CC: Arnd Bergmann , Linux Kernel Mailing List , Thomas Gleixner , John Stultz , Alexandre Belloni , Stephen Boyd , Florian Weimer , Palmer Dabbelt , Alistair Francis , GNU C Library , Karel Zak , Lennart Poettering , OGAWA Hirofumi From: hpa@zytor.com Message-ID: <0089C4CC-DD85-48A1-869B-A9D71852BEC7@zytor.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On August 14, 2019 9:26:36 AM PDT, David Laight wrote: >From: Theodore Y=2E Ts'o >> Sent: 14 August 2019 01:06 >> On Tue, Aug 13, 2019 at 10:30:34AM -0700, Linus Torvalds wrote: >> > >> > 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"=2E >>=20 >> As I recall (and I may or may not have been original for the original >> sys_tz; it was many years ago, and my memories of 1992 are a bit >> fuzzy) the only reason why we added it was because x86 systems that >> were dual-booting with Windows had a RTC which ticked localtime, and >> originally, the system time was fetched from the RTC in early boot, >> and then when the timezone was set, the time would be warped so it >> would be correct=2E > >x86 systems are very likely to have the RTC set by the bios config=2E >In which case it will almost certainly get set to local time=2E >It is certainly the default for windows installs - I don't even know >if you have any other option=2E > >The 'real fun' (tm) happens when a dual boot system changes from >winter to summer time=2E >ISTR that it is quite easy to get both (or more) OS to change the >RTC by an hour (I went home an hour early one year)=2E >Although the x86 RTC chip has a bit defined for 'summertime', nothing >sets it (at least when I looked)=2E > > David > >- >Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, >MK1 1PT, UK >Registration No: 1397386 (Wales) I believe Windows 10 changed the default RTC to UTC, although perhaps only= if running under UEFI=2E --=20 Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E