Reference: https://src.fedoraproject.org/rpms/dhcp/blob/rawhide/f/0025-bind-Detect-system-time-changes.patch
From ef4f5e80d8a1ea1507829ea6f5214f276478f475 Mon Sep 17 00:00:00 2001
From: Pavel Zhukov <pzhukov@redhat.com>
Date: Tue, 22 Oct 2019 16:23:24 +0200
Subject: [PATCH 25/27] bind: Detect system time changes
Cc: pzhukov@redhat.com

---
 bind/bind/lib/isc/include/isc/result.h    |  4 ++-
 bind/bind/lib/isc/include/isc/util.h      |  4 +++
 bind/bind/lib/isc/result.c                |  2 ++
 bind/bind/lib/isc/unix/app.c              | 41 ++++++++++++++++++++++++++++---
 bind/bind/lib/isc/unix/include/isc/time.h | 20 +++++++++++++++
 bind/bind/lib/isc/unix/time.c             | 22 +++++++++++++++++
 6 files changed, 89 insertions(+), 4 deletions(-)

diff --git a/bind/bind/lib/isc/include/isc/result.h b/bind/bind/lib/isc/include/isc/result.h
index 0389efa..0e35f98 100644
--- a/bind/bind/lib/isc/include/isc/result.h
+++ b/bind/bind/lib/isc/include/isc/result.h
@@ -89,7 +89,9 @@
 #define ISC_R_DISCFULL			67	/*%< disc full */
 #define ISC_R_DEFAULT			68	/*%< default */
 #define ISC_R_IPV4PREFIX		69	/*%< IPv4 prefix */
-#define ISC_R_NRESULTS 			70
+#define ISC_R_TIMESHIFTED               70      /*%< system time changed */
+/*% Not a result code: the number of results. */
+#define ISC_R_NRESULTS 			71
 
 ISC_LANG_BEGINDECLS
 
diff --git a/bind/bind/lib/isc/include/isc/util.h b/bind/bind/lib/isc/include/isc/util.h
index 973c348..cceeb5e 100644
--- a/bind/bind/lib/isc/include/isc/util.h
+++ b/bind/bind/lib/isc/include/isc/util.h
@@ -289,6 +289,10 @@ extern void mock_assert(const int result, const char* const expression,
  * Time
  */
 #define TIME_NOW(tp) 	RUNTIME_CHECK(isc_time_now((tp)) == ISC_R_SUCCESS)
+#ifdef CLOCK_BOOTTIME
+#define TIME_MONOTONIC(tp) 	RUNTIME_CHECK(isc_time_boottime((tp)) == ISC_R_SUCCESS)
+#endif
+
 
 /*%
  * Alignment
diff --git a/bind/bind/lib/isc/result.c b/bind/bind/lib/isc/result.c
index a9db132..7c04831 100644
--- a/bind/bind/lib/isc/result.c
+++ b/bind/bind/lib/isc/result.c
@@ -105,6 +105,7 @@ static const char *description[ISC_R_NRESULTS] = {
 	"disc full",				/*%< 67 */
 	"default",				/*%< 68 */
 	"IPv4 prefix",				/*%< 69 */
+        "time changed",                         /*%< 70 */
 };
 
 static const char *identifier[ISC_R_NRESULTS] = {
@@ -178,6 +179,7 @@ static const char *identifier[ISC_R_NRESULTS] = {
 	"ISC_R_DISCFULL",
 	"ISC_R_DEFAULT",
 	"ISC_R_IPV4PREFIX",
+        "ISC_R_TIMESHIFTED",
 };
 
 #define ISC_RESULT_RESULTSET			2
diff --git a/bind/bind/lib/isc/unix/app.c b/bind/bind/lib/isc/unix/app.c
index a6e9882..dbd23f7 100644
--- a/bind/bind/lib/isc/unix/app.c
+++ b/bind/bind/lib/isc/unix/app.c
@@ -442,15 +442,51 @@ isc__app_ctxonrun(isc_appctx_t *ctx0, isc_mem_t *mctx, isc_task_t *task,
 static isc_result_t
 evloop(isc__appctx_t *ctx) {
 	isc_result_t result;
+        isc_time_t now;
+#ifdef CLOCK_BOOTTIME
+        isc_time_t monotonic;
+        uint64_t diff  = 0;
+#else
+        isc_time_t prev;
+        TIME_NOW(&prev);
+#endif
+
+
+
 
 	while (!ctx->want_shutdown) {
 		int n;
-		isc_time_t when, now;
+		isc_time_t when;
+                
 		struct timeval tv, *tvp;
 		isc_socketwait_t *swait;
 		bool readytasks;
 		bool call_timer_dispatch = false;
 
+                uint64_t us; 
+
+#ifdef CLOCK_BOOTTIME
+                // TBD macros for following three lines
+                TIME_NOW(&now);
+                TIME_MONOTONIC(&monotonic);
+                INSIST(now.seconds > monotonic.seconds)
+                us = isc_time_microdiff (&now, &monotonic);
+                if (us < diff){ 
+                  us = diff - us;
+                  if (us > 1000000){ // ignoring shifts less than one second
+                    return ISC_R_TIMESHIFTED;
+                  };
+                  diff = isc_time_microdiff (&now, &monotonic);
+                } else {
+                  diff = isc_time_microdiff (&now, &monotonic);
+                  // not implemented
+                }
+#else
+                TIME_NOW(&now);
+                if (isc_time_compare (&now, &prev) < 0)
+                  return ISC_R_TIMESHIFTED;
+                TIME_NOW(&prev);
+#endif                
 		/*
 		 * Check the reload (or suspend) case first for exiting the
 		 * loop as fast as possible in case:
@@ -475,9 +511,8 @@ evloop(isc__appctx_t *ctx) {
 			if (result != ISC_R_SUCCESS)
 				tvp = NULL;
 			else {
-				uint64_t us;
-
 				TIME_NOW(&now);
+
 				us = isc_time_microdiff(&when, &now);
 				if (us == 0)
 					call_timer_dispatch = true;
diff --git a/bind/bind/lib/isc/unix/include/isc/time.h b/bind/bind/lib/isc/unix/include/isc/time.h
index b864c29..5dd43c9 100644
--- a/bind/bind/lib/isc/unix/include/isc/time.h
+++ b/bind/bind/lib/isc/unix/include/isc/time.h
@@ -132,6 +132,26 @@ isc_time_isepoch(const isc_time_t *t);
  *\li	't' is a valid pointer.
  */
 
+#ifdef CLOCK_BOOTTIME
+isc_result_t
+isc_time_boottime(isc_time_t *t);
+/*%<
+ * Set 't' to monotonic time from previous boot
+ * it's not affected by system time change. It also
+ * includes the time system was suspended
+ *
+ * Requires:
+ *\li	't' is a valid pointer.
+ *
+ * Returns:
+ *
+ *\li	Success
+ *\li	Unexpected error
+ *		Getting the time from the system failed.
+ */
+#endif /* CLOCK_BOOTTIME */
+ 
+
 isc_result_t
 isc_time_now(isc_time_t *t);
 /*%<
diff --git a/bind/bind/lib/isc/unix/time.c b/bind/bind/lib/isc/unix/time.c
index 8edc9df..fe0bb91 100644
--- a/bind/bind/lib/isc/unix/time.c
+++ b/bind/bind/lib/isc/unix/time.c
@@ -498,3 +498,25 @@ isc_time_formatISO8601ms(const isc_time_t *t, char *buf, unsigned int len) {
 			 t->nanoseconds / NS_PER_MS);
 	}
 }
+
+
+#ifdef CLOCK_BOOTTIME
+isc_result_t
+isc_time_boottime(isc_time_t *t) {
+  struct timespec ts;
+  
+  char strbuf[ISC_STRERRORSIZE];
+
+  if (clock_gettime (CLOCK_BOOTTIME, &ts) != 0){
+    isc__strerror(errno, strbuf, sizeof(strbuf));
+    UNEXPECTED_ERROR(__FILE__, __LINE__, "%s", strbuf);
+    return (ISC_R_UNEXPECTED);    
+  }
+
+  t->seconds = ts.tv_sec;
+  t->nanoseconds = ts.tv_nsec;
+
+  return (ISC_R_SUCCESS);
+  
+};
+#endif
-- 
2.14.5

