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    SubjectRe: New kernel interface for sys_tz and timewarp?
    On 13/08/2019 10:30:34-0700, Linus Torvalds wrote:
    > On Tue, Aug 13, 2019 at 2:06 AM Arnd Bergmann <arnd@arndb.de> 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

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