ntpd: explain why scripts can be run in quick succession

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

diff --git a/examples/var_service/ntpd/ntp.script b/examples/var_service/ntpd/ntp.script
index 90299ae..76c34bf 100755 (executable)
--- a/examples/var_service/ntpd/ntp.script
+++ b/examples/var_service/ntpd/ntp.script
@@ -1,10 +1,12 @@
 #!/bin/sh
 
-exec 2>/dev/null
-echo "`tail -n 99 "$0.log"`" >"$0.log"
-
-exec >>"$0.log"
-exec 2>&1
+# Note that there is no provision to prevent several copies of the script
+# to be run in quick succession. In fact, it happens rather often
+# if initial syncronization results in a step.
+# You will see "step" and then "stratum" script runs, sometimes
+# as close as only 0.002 seconds apart.
+#
+# Script should be ready to deal with this.
 
 dt=`date '+%Y-%m-%d %H:%M:%S'`
 
@@ -13,17 +15,23 @@ if test x"$stratum" != x"" \
 && test 4 -ge "$stratum" \
 && test 128 -le "$poll_interval" \
 ; then
+       echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
        echo "$dt: $1"\
                "freq_drift_ppm=$freq_drift_ppm"\
                "offset=$offset"\
                "stratum=$stratum"\
                "poll_interval=$poll_interval,"\
-               "setting hardware clock"
+               "setting hardware clock"\
+               >>"$0.log.$$"
+       mv -- "$0.log.$$" "$0.log"
        exec hwclock --systohc
 fi
 
+echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
 echo "$dt: $1"\
        "freq_drift_ppm=$freq_drift_ppm"\
        "offset=$offset"\
        "stratum=$stratum"\
        "poll_interval=$poll_interval"\
+       >>"$0.log.$$"
+mv -- "$0.log.$$" "$0.log"

diff --git a/networking/ntpd.c b/networking/ntpd.c
index 95dfdb1..04df3fa 100644 (file)
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -735,6 +735,13 @@ send_query_to_peer(peer_t *p)
 }
 
 
+/* Note that there is no provision to prevent several run_scripts
+ * to be done in quick succession. In fact, it happens rather often
+ * if initial syncronization results in a step.
+ * You will see "step" and then "stratum" script runs, sometimes
+ * as close as only 0.002 seconds apart.
+ * Script should be ready to deal with this.
+ */
 static void run_script(const char *action, double offset)
 {
        char *argv[3];
@@ -1185,8 +1192,8 @@ update_local_clock(peer_t *p)
        abs_offset = fabs(offset);
 
 #if 0
-       /* If needed, -S script can detect this by looking at $offset
-        * env var and kill parent */
+       /* If needed, -S script can do it by looking at $offset
+        * env var and killing parent */
        /* If the offset is too large, give up and go home */
        if (abs_offset > PANIC_THRESHOLD) {
                bb_error_msg_and_die("offset %f far too big, exiting", offset);
@@ -2007,7 +2014,7 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
                nfds = poll(pfd, i, timeout * 1000);
                gettime1900d(); /* sets G.cur_time */
                if (nfds <= 0) {
-                       if (G.cur_time - G.last_script_run > 11*60) {
+                       if (G.script_name && G.cur_time - G.last_script_run > 11*60) {
                                /* Useful for updating battery-backed RTC and such */
                                run_script("periodic", G.last_update_offset);
                                gettime1900d(); /* sets G.cur_time */