[libvirt] [PATCHv2 1/4] util: new function virTimeLocalOffsetFromUTC

[Laine Stump]

On 05/22/2014 09:49 PM, Marcelo Tosatti wrote:
> On Thu, May 22, 2014 at 02:07:27PM +0300, Laine Stump wrote:
>> Since there isn't a single libc API to get this value, this patch
>> supplies one which gets the value by grabbing current UTC, then
>> converting that into a struct tm with localtime_r(), then back to a
>> time_t using mktime; it again does the same operation, but using
>> gmtime_r() instead (for UTC). It then subtracts utc time from the
>> localtime, and finally adjusts if dst is set in the localtime timeinfo
>> (because for some reason mktime doesn't take that into account).
>>
>> This function should be POSIX-compliant, and is threadsafe, but not
>> async signal safe. If it was ever necessary to know this value in a
>> child process, we could cache it with a one-time init function when
>> libvirtd starts, then just supply the cached value, but that
>> complexity isn't needed for current usage.
>> ---
>>
>> Change from V1: add test cases with TZ set to different values (if
>> someone knows how to force DST on/off, I would gladly add some test
>> cases for this as well).
>
> man tzset:
>
>        The second format is used when there is daylight saving time:
>
>               std offset dst [offset],start[/time],end[/time]

Aha! And combining that with the "VIR" timezone idea that we're already
using, I've found that the following string *does* set DST:

TZ="VIR02:30VID,0,365"

while the following *doesn't* (at least not today :-):

TZ="VIR02:30VID,300,365"

So I can add the former as a test case.

Thanks!