This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: New kernel interface for sys_tz and timewarp?
- From: Lennart Poettering <mzxreary at 0pointer dot de>
- To: Arnd Bergmann <arnd at arndb dot de>
- Cc: "Theodore Y. Ts'o" <tytso at mit dot edu>, Linus Torvalds <torvalds at linux-foundation dot org>, 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>, "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>, OGAWA Hirofumi <hirofumi at mail dot parknet dot co dot jp>
- Date: Wed, 14 Aug 2019 11:09:36 +0200
- Subject: Re: New kernel interface for sys_tz and timewarp?
- References: <CAK8P3a0VxM1BkjY1D2FfHi6L-ho_NH3v3+gBu45EfpjLF5NU5w@mail.gmail.com> <CAHk-=wiO2CWONDBud4nxoPgUJN1JEewFWhHa5wAqY8G5rrTXRQ@mail.gmail.com> <20190814000622.GB20365@mit.edu> <CAK8P3a1CXRETxn6Gh_cOxM3rZ-wUwVDu-7=yEwjqOY=uEdC6OQ@mail.gmail.com>
On Mi, 14.08.19 10:31, Arnd Bergmann (arnd@arndb.de) wrote:
> - glibc stops passing the caller timezone argument to the kernel
> - the distro kernel disables CONFIG_RTC_HCTOSYS,
> CONFIG_RTC_SYSTOHC and CONFIG_GENERIC_CMOS_UPDATE
What's the benefit of letting userspace do this? It sounds a lot more
fragile to leave this syncing to userspace if the kernel can do this
trivially on its own.
IIRC there are uses in kernel that use CLOCK_REALTIME already before
userspace starts. e.g. iirc networking generally prefers
CLOCK_REALTIME timestamps over CLOCK_MONOTONIC timestamps
(i.e. SO_TIMESTAMP and friends are still CLOCK_REALTIME only so far,
unless I am missing something). If the kernel comes up with a
CLOCK_REALTIME that starts at 0 this is pretty annoying I
figure... Hence, so far I suggested to distros to continue turning on
the options above, and let the kernel do this on its own without
involving userspace in that.
Lennart
--
Lennart Poettering, Berlin