hwclock: make it report system/rtc clock difference

function                                             old     new   delta
rtc_tm2time                                            -      89     +89
read_rtc                                              23      86     +63
rtc_read_tm                                            -      49     +49
hwclock_main                                         428     466     +38
rtcwake_main                                         453     477     +24
rtc_read_time                                        142       -    -142
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 3/0 up/down: 263/-142)          Total: 121 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

4 files changed, 53 insertions, 24 deletions

diff --git a/include/rtc_.h b/include/rtc_.h
index 74bb695a0..2b4ae778d 100644
--- a/include/rtc_.h
+++ b/include/rtc_.h
@@ -11,9 +11,11 @@
 
 PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
 
-extern int rtc_adjtime_is_utc(void) FAST_FUNC;
-extern int rtc_xopen(const char **default_rtc, int flags) FAST_FUNC;
-extern time_t rtc_read_time(int fd, int utc) FAST_FUNC;
+int rtc_adjtime_is_utc(void) FAST_FUNC;
+int rtc_xopen(const char **default_rtc, int flags) FAST_FUNC;
+void rtc_read_tm(struct tm *tm, int fd) FAST_FUNC;
+time_t rtc_tm2time(struct tm *tm, int utc) FAST_FUNC;
+
 
 /*
  * Everything below this point has been copied from linux/rtc.h
diff --git a/libbb/rtc.c b/libbb/rtc.c
index 2f38b8a7e..9807e1cf9 100644
--- a/libbb/rtc.c
+++ b/libbb/rtc.c
@@ -59,15 +59,17 @@ int FAST_FUNC rtc_xopen(const char **default_rtc, int flags)
         return xopen(*default_rtc, flags);
 }
 
-time_t FAST_FUNC rtc_read_time(int fd, int utc)
+void FAST_FUNC rtc_read_tm(struct tm *tm, int fd)
 {
-        struct tm tm;
-        char *oldtz = 0;
-        time_t t = 0;
+        memset(tm, 0, sizeof(*tm));
+        xioctl(fd, RTC_RD_TIME, tm);
+        tm->tm_isdst = -1; /* "not known" */
+}
 
-        memset(&tm, 0, sizeof(struct tm));
-        xioctl(fd, RTC_RD_TIME, &tm);
-        tm.tm_isdst = -1; /* not known */
+time_t FAST_FUNC rtc_tm2time(struct tm *tm, int utc)
+{
+        char *oldtz = oldtz; /* for compiler */
+        time_t t;
 
         if (utc) {
                 oldtz = getenv("TZ");
@@ -75,7 +77,7 @@ time_t FAST_FUNC rtc_read_time(int fd, int utc)
                 tzset();
         }
 
-        t = mktime(&tm);
+        t = mktime(tm);
 
         if (utc) {
                 unsetenv("TZ");
diff --git a/util-linux/hwclock.c b/util-linux/hwclock.c
index 08e5bd701..606721e2c 100644
--- a/util-linux/hwclock.c
+++ b/util-linux/hwclock.c
@@ -20,34 +20,54 @@
 
 static const char *rtcname;
 
-static time_t read_rtc(int utc)
+static time_t read_rtc(struct timeval *sys_tv, int utc)
 {
-        time_t ret;
+        struct tm tm;
         int fd;
+        int before;
 
         fd = rtc_xopen(&rtcname, O_RDONLY);
-        ret = rtc_read_time(fd, utc);
+
+        rtc_read_tm(&tm, fd);
+        before = tm.tm_sec;
+        while (1) {
+                rtc_read_tm(&tm, fd);
+                gettimeofday(sys_tv, NULL);
+                if (before != tm.tm_sec)
+                        break;
+        }
+
         if (ENABLE_FEATURE_CLEAN_UP)
                 close(fd);
 
-        return ret;
+        return rtc_tm2time(&tm, utc);
 }
 
 static void show_clock(int utc)
 {
-        //struct tm *ptm;
+        struct timeval sys_tv;
         time_t t;
+        long diff;
         char *cp;
 
-        t = read_rtc(utc);
-        //ptm = localtime(&t);  /* Sets 'tzname[]' */
+        t = read_rtc(&sys_tv, utc);
 
         cp = ctime(&t);
         strchrnul(cp, '\n')[0] = '\0';
 
         //printf("%s  0.000000 seconds %s\n", cp, utc ? "" : (ptm->tm_isdst ? tzname[1] : tzname[0]));
-        /* 0.000000 stand for unimplemented difference between RTC and system clock */
-        printf("%s  0.000000 seconds\n", cp);
+        diff = sys_tv.tv_sec - t;
+        if (diff < 0 /*&& tv.tv_usec != 0*/) {
+                /* Why? */
+                /* diff >= 0 is ok:   diff < 0, can't just use tv.tv_usec: */
+                /*   45.520820          43.520820 */
+                /* - 44.000000        - 45.000000 */
+                /* =  0.520820        = -1.479180, not -2.520820! */
+                diff++;
+                /* should be 1000000 - tv.tv_usec, but then we must check tv.tv_usec != 0 */
+                sys_tv.tv_usec = 999999 - sys_tv.tv_usec;
+        }
+        printf("%s  %ld.%06lu seconds\n", cp, diff, (unsigned long)sys_tv.tv_usec);
 }
 
 static void to_sys_clock(int utc)
@@ -58,7 +78,7 @@ static void to_sys_clock(int utc)
         tz.tz_minuteswest = timezone/60 - 60*daylight;
         tz.tz_dsttime = 0;
 
-        tv.tv_sec = read_rtc(utc);
+        tv.tv_sec = read_rtc(NULL, utc);
         tv.tv_usec = 0;
         if (settimeofday(&tv, &tz))
                 bb_perror_msg_and_die("settimeofday() failed");
@@ -79,15 +99,15 @@ static void from_sys_clock(int utc)
 
                 gettimeofday(&tv, NULL);
 
+                t = tv.tv_sec;
                 rem_usec = 1000000 - tv.tv_usec;
                 if (rem_usec < 1024) {
                         /* Less than 1ms to next second. Good enough */
  small_rem:
-                        tv.tv_sec++;
+                        t++;
                 }
 
                 /* Prepare tm */
-                t = tv.tv_sec;
                 if (utc)
                         gmtime_r(&t, &tm); /* may read /etc/xxx (it takes time) */
                 else
diff --git a/util-linux/rtcwake.c b/util-linux/rtcwake.c
index 049f699f5..64c3e7ed7 100644
--- a/util-linux/rtcwake.c
+++ b/util-linux/rtcwake.c
@@ -160,7 +160,12 @@ int rtcwake_main(int argc UNUSED_PARAM, char **argv)
 
         /* relative or absolute alarm time, normalized to time_t */
         sys_time = time(NULL);
-        rtc_time = rtc_read_time(fd, utc);
+        {
+                struct tm tm;
+                rtc_read_tm(&tm, fd);
+                rtc_time = rtc_tm2time(&tm, utc);
+        }
+
 
         if (alarm_time) {
                 if (alarm_time < sys_time)