[libvirt] [PATCHv2] util: fix virTimeLocalOffsetFromUTC DST processing

[Eric Blake]

On 05/28/2014 04:46 AM, Laine Stump wrote:
> The original version of virTimeLocalOffsetFromUTC() would fail for
> certain times of the day if daylight savings time was active. This
> could most easily be seen by uncommenting the TEST_LOCALOFFSET() cases
> that include a DST setting.


> 
>  src/util/virtime.c  |  3 +++
>  tests/virtimetest.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 56 insertions(+), 8 deletions(-)
> 
> diff --git a/src/util/virtime.c b/src/util/virtime.c
> index 3a56400..c69dff1 100644
> --- a/src/util/virtime.c
> +++ b/src/util/virtime.c
> @@ -377,6 +377,9 @@ virTimeLocalOffsetFromUTC(long *offset)
>          return -1;
>      }
>  
> +    /* tell mktime to figure out itself whether or not DST is in effect */
> +    gmtimeinfo.tm_isdst = -1;

As pointed out by Wangrui, you also need to fix the bogus reference to
localtime_r() in the comments at the start of the function.

ACK with that change; worth having in 1.2.5.  The rest of what follows
is up to you if you ignore it.

> +
> +/* return true if the date is Jan 1 or Dec 31 (localtime) */
> +static bool
> +IsJan1OrDec31(void)

Function names are usually camelCase, not StudlyCaps (s/Is/is/).
Bikeshedding: maybe name it isNearYearEnd()?

> +
> +    if (!IsJan1OrDec31()) {
> +        /* experiments have shown that the following tests will fail
> +         * during certain hours of Dec 31 or Jan 1 (depending on the
> +         * TZ setting in the shell running the test, but in general
> +         * for a period that apparently starts at 00:00:00 UTC Jan 1
> +         * and continues for 1 - 2 hours). We've determined this is
> +         * due to our inability to specify a timezone with DST on/off
> +         * settings that make it truly *always* on DST - i.e. it is a
> +         * failing of the test data, *not* of the function we are
> +         * testing. So to test as much as possible, we still run these
> +         * tests, except on Dec 31 and Jan 1.

Awesome comment; thanks :)

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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