On Fri, May 23, 2014 at 02:43:08PM +0300, Laine Stump wrote:
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!
Btw TZ also contains != 1hour daylight offset information (see that section of man tzset). I'll send a QEMU patch to add a command to query the RTC offset.