fix hwclock_apply_localtime_delta() to properly handle negative TZ offset

Localtime may be a negative number, i.e. GMT-7. Fix based on a
patch from Kelly Anderson <kelly@silka.with-linux.com>.

src/main.c

@@ -1056,11 +1056,11 @@ int main(int argc, char *argv[]) {
                         goto finish;
 
                 if (hwclock_is_localtime() > 0) {
-                        int min;
+                        int err, min;
 
-                        min = hwclock_apply_localtime_delta();
-                        if (min < 0)
-                                log_error("Failed to apply local time delta: %s", strerror(-min));
+                        err = hwclock_apply_localtime_delta(&min);
+                        if (err < 0)
+                                log_error("Failed to apply local time delta: %s", strerror(-err));
                         else
                                 log_info("RTC configured in localtime, applying delta of %i minutes to system time.", min);
                 }

src/timedated.c

@@ -332,7 +332,7 @@ static DBusHandlerResult timedate_message_handler(
                                 struct tm *tm;
 
                                 /* 2. Teach kernel new timezone */
-                                hwclock_apply_localtime_delta();
+                                hwclock_apply_localtime_delta(NULL);
 
                                 /* 3. Sync RTC from system clock, with the new delta */
                                 assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
@@ -382,7 +382,7 @@ static DBusHandlerResult timedate_message_handler(
 
                         /* 2. Teach kernel new timezone */
                         if (local_rtc)
-                                hwclock_apply_localtime_delta();
+                                hwclock_apply_localtime_delta(NULL);
                         else
                                 hwclock_reset_localtime_delta();
 

src/util.c

@@ -4905,7 +4905,7 @@ int hwclock_is_localtime(void) {
         return local;
 }
 
-int hwclock_apply_localtime_delta(void) {
+int hwclock_apply_localtime_delta(int *min) {
         const struct timeval *tv_null = NULL;
         struct timespec ts;
         struct tm *tm;
@@ -4926,8 +4926,9 @@ int hwclock_apply_localtime_delta(void) {
          */
         if (settimeofday(tv_null, &tz) < 0)
                 return -errno;
-
-        return minuteswest;
+        if (min)
+                *min = minuteswest;
+        return 0;
 }
 
 int hwclock_reset_localtime_delta(void) {

src/util.h

@@ -434,8 +434,7 @@ int fchmod_umask(int fd, mode_t mode);
 int conf_files_list(char ***strv, const char *suffix, const char *dir, ...);
 
 int hwclock_is_localtime(void);
-
-int hwclock_apply_localtime_delta(void);
+int hwclock_apply_localtime_delta(int *min);
 int hwclock_reset_localtime_delta(void);
 int hwclock_get_time(struct tm *tm);
 int hwclock_set_time(const struct tm *tm);