hwclock: fix sizeof bug (used it on pointer, not array); make --systohc exact

function                                             old     new   delta
hwclock_main                                         329     428     +99
rtc_adjtime_is_utc                                   138     134      -4
edir                                                 365     354     -11
read_rtc                                              39      23     -16
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/3 up/down: 99/-31)             Total: 68 bytes

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

1 files changed, 70 insertions, 24 deletions

diff --git a/util-linux/hwclock.c b/util-linux/hwclock.c
index 6dff57f09..08e5bd701 100644
--- a/util-linux/hwclock.c
+++ b/util-linux/hwclock.c
@@ -27,27 +27,12 @@ static time_t read_rtc(int utc)
 
         fd = rtc_xopen(&rtcname, O_RDONLY);
         ret = rtc_read_time(fd, utc);
-        close(fd);
+        if (ENABLE_FEATURE_CLEAN_UP)
+                close(fd);
 
         return ret;
 }
 
-static void write_rtc(time_t t, int utc)
-{
-        struct tm tm;
-        int rtc = rtc_xopen(&rtcname, O_WRONLY);
-
-        if (utc)
-                gmtime_r(&t, &tm);
-        else
-                localtime_r(&t, &tm);
-        tm.tm_isdst = 0;
-
-        xioctl(rtc, RTC_SET_TIME, &tm);
-
-        close(rtc);
-}
-
 static void show_clock(int utc)
 {
         //struct tm *ptm;
@@ -58,10 +43,10 @@ static void show_clock(int utc)
         //ptm = localtime(&t);  /* Sets 'tzname[]' */
 
         cp = ctime(&t);
-        if (cp[0])
-                cp[strlen(cp) - 1] = '\0';
+        strchrnul(cp, '\n')[0] = '\0';
 
-        //printf("%s  %.6f seconds %s\n", cp, 0.0, utc ? "" : (ptm->tm_isdst ? tzname[1] : tzname[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);
 }
 
@@ -81,12 +66,73 @@ static void to_sys_clock(int utc)
 
 static void from_sys_clock(int utc)
 {
+#define TWEAK_USEC 200
+        struct tm tm;
         struct timeval tv;
+        unsigned adj = TWEAK_USEC;
+        int rtc = rtc_xopen(&rtcname, O_WRONLY);
+
+        /* Try to catch the moment when whole second is close */
+        while (1) {
+                unsigned rem_usec;
+                time_t t;
+
+                gettimeofday(&tv, NULL);
+
+                rem_usec = 1000000 - tv.tv_usec;
+                if (rem_usec < 1024) {
+                        /* Less than 1ms to next second. Good enough */
+ small_rem:
+                        tv.tv_sec++;
+                }
+
+                /* Prepare tm */
+                t = tv.tv_sec;
+                if (utc)
+                        gmtime_r(&t, &tm); /* may read /etc/xxx (it takes time) */
+                else
+                        localtime_r(&t, &tm); /* same */
+                tm.tm_isdst = 0;
+
+                /* gmtime/localtime took some time, re-get cur time */
+                gettimeofday(&tv, NULL);
+
+                if (tv.tv_sec < t /* may happen if rem_usec was < 1024 */
+                 || (tv.tv_sec == t && tv.tv_usec < 1024)
+                ) {
+                        /* We are not too far into next second. Good. */
+                        break;
+                }
+                adj += 32; /* 2^(10-5) = 2^5 = 32 iterations max */
+                if (adj >= 1024) {
+                        /* Give up trying to sync */
+                        break;
+                }
+
+                /* Try to sync up by sleeping */
+                rem_usec = 1000000 - tv.tv_usec;
+                if (rem_usec < 1024) {
+                        goto small_rem; /* already close, don't sleep */
+                }
+                /* Need to sleep.
+                 * Note that small adj on slow processors can make us
+                 * to always overshoot tv.tv_usec < 1024 check on next
+                 * iteration. That's why adj is increased on each iteration.
+                 * This also allows it to be reused as a loop limiter.
+                 */
+                usleep(rem_usec - adj);
+        }
+
+        xioctl(rtc, RTC_SET_TIME, &tm);
+
+        /* Debug aid to find "good" TWEAK_USEC.
+         * Look for a value which makes tv_usec close to 999999 or 0.
+         * for 2.20GHz Intel Core 2: TWEAK_USEC ~= 200
+         */
+        //bb_error_msg("tv.tv_usec:%d adj:%d", (int)tv.tv_usec, adj);
 
-        gettimeofday(&tv, NULL);
-        //if (gettimeofday(&tv, NULL))
-        //      bb_perror_msg_and_die("gettimeofday() failed");
-        write_rtc(tv.tv_sec, utc);
+        if (ENABLE_FEATURE_CLEAN_UP)
+                close(rtc);
 }
 
 #define HWCLOCK_OPT_LOCALTIME   0x01