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

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).