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Date:   Tue, 13 Aug 2019 20:06:23 -0400
From:   "Theodore Y. Ts'o" <tytso@mit.edu>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Alistair Francis <alistair.francis@wdc.com>,
        GNU C Library <libc-alpha@sourceware.org>,
        Karel Zak <kzak@redhat.com>,
        Lennart Poettering <lennart@poettering.net>,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: New kernel interface for sys_tz and timewarp?
Message-ID: <20190814000622.GB20365@mit.edu>
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        Florian Weimer <fweimer@redhat.com>,
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        GNU C Library <libc-alpha@sourceware.org>,
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        Lennart Poettering <lennart@poettering.net>,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
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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".

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.

Trying to use this for anything else is probably a bad idea, and in a
world where we can have initrd's and reading the RTC gets done by
userspace as opposed to kernel, it probably doesn't make any sence to
keep it.

Cheers,

					- Ted