split some rtc funcs out of hwclock and into an rtc header/lib so that the new rtcwake applet as well as hwclock can utilize the same code

libbb/rtc.c

@@ -0,0 +1,86 @@
+/*
+ * Common RTC functions
+ */
+
+#include "libbb.h"
+#include "rtc_.h"
+
+#if ENABLE_FEATURE_HWCLOCK_ADJTIME_FHS
+# define ADJTIME_PATH "/var/lib/hwclock/adjtime"
+#else
+# define ADJTIME_PATH "/etc/adjtime"
+#endif
+
+int rtc_adjtime_is_utc(void)
+{
+	int utc = 0;
+	FILE *f = fopen(ADJTIME_PATH, "r");
+
+	if (f) {
+		RESERVE_CONFIG_BUFFER(buffer, 128);
+
+		while (fgets(buffer, sizeof(buffer), f)) {
+			int len = strlen(buffer);
+
+			while (len && isspace(buffer[len - 1]))
+				len--;
+
+			buffer[len] = 0;
+
+			if (strncmp(buffer, "UTC", 3) == 0) {
+				utc = 1;
+				break;
+			}
+		}
+		fclose(f);
+
+		RELEASE_CONFIG_BUFFER(buffer);
+	}
+
+	return utc;
+}
+
+int rtc_xopen(const char *default_rtc, int flags)
+{
+	int rtc;
+
+	if (!default_rtc) {
+		rtc = open("/dev/rtc", flags);
+		if (rtc >= 0)
+			return rtc;
+		rtc = open("/dev/rtc0", flags);
+		if (rtc >= 0)
+			return rtc;
+		default_rtc = "/dev/misc/rtc";
+	}
+
+	return xopen(default_rtc, flags);
+}
+
+time_t rtc_read_time(int fd, int utc)
+{
+	struct tm tm;
+	char *oldtz = 0;
+	time_t t = 0;
+
+	memset(&tm, 0, sizeof(struct tm));
+	xioctl(fd, RTC_RD_TIME, &tm);
+	tm.tm_isdst = -1; /* not known */
+
+	if (utc) {
+		oldtz = getenv("TZ");
+		putenv((char*)"TZ=UTC0");
+		tzset();
+	}
+
+	t = mktime(&tm);
+
+	if (utc) {
+		unsetenv("TZ");
+		if (oldtz)
+			putenv(oldtz - 3);
+		tzset();
+	}
+
+	return t;
+}