This new function returns the GMT offset relative to its
argument. It is used in this patch to fix two bugs:
1) On platforms that the tm struct excludes tm_gmtoff,
hwclock assumes a one hour DST offset. This can cause
an incorrect kernel timezone setting. For example:
Current; with tm_gmtoff illustrates the correct offset:
$ TZ="Australia/Lord_Howe" hwclock --hctosys --test | grep settimeofday
Calling settimeofday(1507494204.192398, -660)
Current; without tm_gmtoff:
$ TZ="Australia/Lord_Howe" hwclock --hctosys --test | grep settimeofday
Calling settimeofday(1507494249.193852, -690)
Patched; without tm_gmtoff:
$ TZ="Australia/Lord_Howe" hwclock --hctosys --test | grep settimeofday
Calling settimeofday(1507494260.194208, -660)
2) ISO 8601 'extended' format requires all time elements
to use a colon (:).
Current invalid ISO 8601:
$ hwclock
2017-10-08 16:25:17.895462-0400
Patched:
$ hwclock
2017-10-08 16:25:34.141895-04:00
Signed-off-by: J William Piggott <elseifthen@xxxxxxx>
---
include/timeutils.h | 1 +
lib/timeutils.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++--
sys-utils/hwclock.c | 8 +------
3 files changed, 68 insertions(+), 9 deletions(-)
diff --git a/include/timeutils.h b/include/timeutils.h
index edd42f7fe..e8a261462 100644
--- a/include/timeutils.h
+++ b/include/timeutils.h
@@ -53,6 +53,7 @@ typedef uint64_t nsec_t;
#define FORMAT_TIMESPAN_MAX 64
int parse_timestamp(const char *t, usec_t *usec);
+int get_gmtoff(const struct tm *tp);
/* flags for strxxx_iso() functions */
enum {
diff --git a/lib/timeutils.c b/lib/timeutils.c
index d38970c10..adc255c33 100644
--- a/lib/timeutils.c
+++ b/lib/timeutils.c
@@ -341,6 +341,65 @@ int parse_timestamp(const char *t, usec_t *usec)
return 0;
}
+/* Returns the difference in seconds between its argument and GMT. If if TP is
+ * invalid or no DST information is available default to UTC, that is, zero.
+ * tzset is called so, for example, 'TZ="UTC" hwclock' will work as expected.
+ * Derived from glibc/time/strftime_l.c
+ */
+int get_gmtoff(const struct tm *tp)
+{
+ if (tp->tm_isdst < 0)
+ return 0;
+
+#if HAVE_TM_GMTOFF
+ return tp->tm_gmtoff;
+#else
+ struct tm tm;
+ struct tm gtm;
+ struct tm ltm = *tp;
+ time_t lt;
+
+ tzset();
+ lt = mktime(<m);
+ /* Check if mktime returning -1 is an error or a valid time_t */
+ if (lt == (time_t) -1) {
+ if (! localtime_r(<, &tm)
+ || ((ltm.tm_sec ^ tm.tm_sec)
+ | (ltm.tm_min ^ tm.tm_min)
+ | (ltm.tm_hour ^ tm.tm_hour)
+ | (ltm.tm_mday ^ tm.tm_mday)
+ | (ltm.tm_mon ^ tm.tm_mon)
+ | (ltm.tm_year ^ tm.tm_year)))
+ return 0;
+ }
+
+ if (! gmtime_r(<, >m))
+ return 0;
+
+ /* Calculate the GMT offset, that is, the difference between the
+ * TP argument (ltm) and GMT (gtm).
+ *
+ * Compute intervening leap days correctly even if year is negative.
+ * Take care to avoid int overflow in leap day calculations, but it's OK
+ * to assume that A and B are close to each other.
+ */
+ int a4 = (ltm.tm_year >> 2) + (1900 >> 2) - ! (ltm.tm_year & 3);
+ int b4 = (gtm.tm_year >> 2) + (1900 >> 2) - ! (gtm.tm_year & 3);
+ int a100 = a4 / 25 - (a4 % 25 < 0);
+ int b100 = b4 / 25 - (b4 % 25 < 0);
+ int a400 = a100 >> 2;
+ int b400 = b100 >> 2;
+ int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
+
+ int years = ltm.tm_year - gtm.tm_year;
+ int days = (365 * years + intervening_leap_days
+ + (ltm.tm_yday - gtm.tm_yday));
+
+ return (60 * (60 * (24 * days + (ltm.tm_hour - gtm.tm_hour))
+ + (ltm.tm_min - gtm.tm_min)) + (ltm.tm_sec - gtm.tm_sec));
+#endif
+}
+
static int format_iso_time(struct tm *tm, suseconds_t usec, int flags, char *buf, size_t bufsz)
{
char *p = buf;
@@ -386,9 +445,14 @@ static int format_iso_time(struct tm *tm, suseconds_t usec, int flags, char *buf
p += len;
}
- if (flags & ISO_8601_TIMEZONE && strftime(p, bufsz, "%z", tm) <= 0)
+ if (flags & ISO_8601_TIMEZONE) {
+ int tmin = get_gmtoff(tm) / 60;
+ int zhour = tmin / 60;
+ int zmin = abs(tmin % 60);
+ len = snprintf(p, bufsz, "%+03d:%02d", zhour,zmin);
+ if (len < 0 || (size_t) len > bufsz)
return -1;
-
+ }
return 0;
}
diff --git a/sys-utils/hwclock.c b/sys-utils/hwclock.c
index c2c20812c..3ac43efee 100644
--- a/sys-utils/hwclock.c
+++ b/sys-utils/hwclock.c
@@ -608,13 +608,7 @@ set_system_clock(const struct hwclock_control *ctl,
const struct timezone tz_utc = { 0 };
broken = localtime(&newtime.tv_sec);
-#ifdef HAVE_TM_GMTOFF
- minuteswest = -broken->tm_gmtoff / 60; /* GNU extension */
-#else
- minuteswest = timezone / 60;
- if (broken->tm_isdst)
- minuteswest -= 60;
-#endif
+ minuteswest = -get_gmtoff(broken) / 60;
if (ctl->debug) {
if (ctl->hctosys && !ctl->universal)
--
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