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Re: New kernel interface for sys_tz and timewarp?

From: Paul Eggert <eggert at cs dot ucla dot edu>
To: Linus Torvalds <torvalds at linux-foundation dot org>, Arnd Bergmann <arnd at arndb dot de>
Cc: Linux Kernel Mailing List <linux-kernel at vger dot kernel dot org>, Thomas Gleixner <tglx at linutronix dot de>, John Stultz <john dot stultz at linaro dot org>, Alexandre Belloni <alexandre dot belloni at bootlin dot com>, Stephen Boyd <sboyd at kernel dot org>, Florian Weimer <fweimer at redhat dot com>, Theodore Ts'o <tytso at mit dot edu>, "H. Peter Anvin" <hpa at zytor dot com>, Palmer Dabbelt <palmer at dabbelt dot com>, Alistair Francis <alistair dot francis at wdc dot com>, GNU C Library <libc-alpha at sourceware dot org>, Karel Zak <kzak at redhat dot com>, Lennart Poettering <lennart at poettering dot net>, OGAWA Hirofumi <hirofumi at mail dot parknet dot co dot jp>
Date: Tue, 13 Aug 2019 10:49:03 -0700
Subject: Re: New kernel interface for sys_tz and timewarp?
References: <CAK8P3a0VxM1BkjY1D2FfHi6L-ho_NH3v3+gBu45EfpjLF5NU5w@mail.gmail.com> <CAHk-=wiO2CWONDBud4nxoPgUJN1JEewFWhHa5wAqY8G5rrTXRQ@mail.gmail.com>

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 defaultspecified in /etc/localtime or suchlike (there is no per-user default). glibcignores the kernel's 'struct timezone' settings for of this, as 'structtimezone' is obsolete/vestigial and doesn't contain enough info to do properconversions anyway.

I've been thinking of adding NetBSD's localtime_rz etc. functions to glibc.These functions let user programs specify the time zone for each conversionbetween time_t and local time, and simplify and/or speed up applications dealingwith many requests coming from different time zones. These functions also ignore'struct timezone'.


There's no need to put any of this stuff into the kernel.

Follow-Ups:
- Re: New kernel interface for sys_tz and timewarp?
  - From: Florian Weimer

References:
- New kernel interface for sys_tz and timewarp?
  - From: Arnd Bergmann
- Re: New kernel interface for sys_tz and timewarp?
  - From: Linus Torvalds

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