RE: New kernel interface for sys_tz and timewarp?

hpa
2019-08-14T16:48:43Z

On August 14, 2019 9:26:36 AM PDT, David Laight <David.Laight@ACULAB.COM> wrote:
>From: Theodore Y. 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".
>>
>> 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.
>
>x86 systems are very likely to have the RTC set by the bios config.
>In which case it will almost certainly get set to local time.
>It is certainly the default for windows installs - I don't even know
>if you have any other option.
>
>The 'real fun' (tm) happens when a dual boot system changes from
>winter to summer time.
>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).
>Although the x86 RTC chip has a bit defined for 'summertime', nothing
>sets it (at least when I looked).
>
> David
>
>-
>Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
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I believe Windows 10 changed the default RTC to UTC, although perhaps only if running under UEFI.
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