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

[Shawn Landden]

On Mon, Mar 23, 2015 at 4:42 AM, Stef Walter <stefw at redhat.com> wrote:
> On 23.03.2015 12:11, Shawn Landden wrote:
>> On Sun, Mar 22, 2015 at 10:32 PM, 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().
>>>
>>> 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 out-of-date timezone from the local database.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...
>> The patch is COMPLETELY WRONG, as timezone offsets are differn't for
>> differn't times due to DST. Even if this is taken into account there
>> are all sorts of races
>> with this information around DST switches.
>
> As with the TimeUSec and RTCTimeUSec properties, it's assumed the caller
> knows the information is out of date the instant they receive it.
Your patch is a whole hour slow during daylight savings time. (The
epoch, when you query the offset for, is standard time as it is during
January.)
>
> But in that case I guess we shouldn't do
> SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE...
Fixed.
>
>> How about a
>> "LocalTimeUSec" property, for those times that the application doesn't
>> have an interest doing timezone calculations and just wants the local
>> time on the other machine.
>
> That's fine with me. Although IMO it's quite unorthodox to have local
> time in an integer value counted since the epoch.
>
> <snip>
>
> Stef
>



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Shawn Landden
ChurchOfGit.com