ntpd: explain why scripts can be run in quick succession

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

2 files changed, 24 insertions, 9 deletions

diff --git a/examples/var_service/ntpd/ntp.script b/examples/var_service/ntpd/ntp.script
index 90299ae8e..76c34bf74 100755
--- 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 95dfdb119..04df3fa7f 100644
--- 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 */