[systemd-devel] [PATCH] timedated: Add a LocalOffset property for timezone offset

[Kay Sievers]

On Mon, Mar 23, 2015 at 3:49 PM, Stef Walter <stefw at redhat.com> wrote:
> On 23.03.2015 15:26, Kay Sievers wrote:
>> On Mon, Mar 23, 2015 at 1:46 PM, David Herrmann <dh.herrmann at gmail.com> wrote:
>>> Hi
>>>
>>> On Mon, Mar 23, 2015 at 6:32 AM, Lennart Poettering
>>> <lennart at poettering.net> wrote:
>>>> On Thu, 19.03.15 14:39, David Herrmann (dh.herrmann at gmail.com) wrote:
>>>>
>>>>> Hmm, so this is a convenience call. You could just set tm.tm_zone
>>>>> locally and use mktime() with the value retrieved by "Timezone"? Yeah,
>>>>> the time-api is awful with global variables, but that's not really our
>>>>> fault, is it?
>>>>
>>>> This would not work, as struct tm's .tm_zone field is not sufficient
>>>> to indicate a timezone. The code would have to set $TZ and call tzset().
>>>
>>> I see. The Unix-way of doing things!
>>>
>>>> Given the simplicity of this I'd probably just merge Stef's
>>>> patch... It *is* kinda nice given that the timezone database is
>>>> constantly updated and having this exposed on the bus so that it is
>>>> accessible remotely has the benefit that you get the actual timezone
>>>> information in effect on the remote system, and not a possible
>>>> out-of-date timezone from the local database. If you follow what I mean...
>>>
>>> ..locale data is also updated regularly but we don't export
>>> locale-files on the bus ;)
>>>
>>> Anyway, if we add pseudo-redundant APIs, I'd go with a "LocalTime"
>>> field as Shawn suggested. This is what the bus-user is interested in,
>>> right? If they need more data (like DST), they should just parse
>>> zoneinfo. And with "LocalTime" we avoid any ambiguity regarding DST.
>>
>> Transmitting several absolute time stamps sounds wrong.
>> Transmitting the offset sounds as wrong as tz_minuteswest is and it got killed
>> for that reason.
>>
>> Why does anybody ever need anything else than the actual UTC time and
>> the configured  timezone of the machine?
>
> Yes, we do. In Cockpit we want to show the server's local time, in the
> server's timezone. This is similar to how GNOME shows you the local time
> in the local timezone.
>
> But we don't have easy access to libc and its zoneinfo file parser from
> javascript running in a browser. We do have access to DBus [0]

But it is not systemd's task to cover for missing functionality in the
cockpit architecture. We should not add redundant interfaces just
provide data for a specific user.

The data systemd provides over the bus is the the same as the running
system provides to the local user: the UTC time + the time zone.
Everything else should be a task of the presentation, in this case
cockpit.

> So obviously we could invent a DBus service called timedated2 (or
> whatever) to do what we need ... but I figured I'd see if timedated
> could do what we needed first.

I don't think so. Systemd covers operating system data, but I doubt it
should provide "remote glibc" functionality.

> It seems that timedatectl itself needs information about remote local
> time, since when connecting remotely over DBus it gets the local time
> wrong. [1]

Yeah, it's currently a mix of local vs. remote data. If timedatctl
should work correctly on a remote host, it needs to fixed.

Kay