Add isc_time_monotonic()

This is to simplify measurements of how long things take.

CHANGES

@@ -1,3 +1,6 @@
+6085.	[func]		Add isc_time_monotonic() to simplify time measurements.
+			[GL !7468]
+
 6084.	[bug]		When BIND was built without jemalloc, the allocator flag
 			ISC_MEM_ZERO could return non-zero memory. [GL #3845]
 

lib/isc/include/isc/time.h

@@ -76,10 +76,35 @@ ISC_LANG_BEGINDECLS
  *\li	'i' is a valid pointer.
  */
 
+#define isc_interval_fromnanosecs(ns) isc_time_fromnanosecs(ns)
+#define isc_interval_tonanosecs(i)    isc_time_tonanosecs(i)
+
 /***
  *** Absolute Times
  ***/
 
+/*%
+ * A linear count of nanoseconds.
+ *
+ * 64 bits of nanoseconds is more than 500 years.
+ */
+typedef uint64_t isc_nanosecs_t;
+
+/*%
+ * Convert linear nanoseconds to an isc_time_t
+ */
+#define isc_nanosecs_fromtime(time) \
+	(NS_PER_SEC * (isc_nanosecs_t)(time).seconds + (time).nanoseconds)
+
+/*%
+ * Construct an isc_time_t from linear nanoseconds
+ */
+#define isc_time_fromnanosecs(ns)                 \
+	((isc_time_t){                            \
+		.seconds = (ns) / NS_PER_SEC,     \
+		.nanoseconds = (ns) % NS_PER_SEC, \
+	})
+
 /*%
  * The contents of this structure are private, and MUST NOT be accessed
  * directly by callers.
@@ -136,6 +161,12 @@ isc_time_isepoch(const isc_time_t *t);
  *\li	't' is a valid pointer.
  */
 
+isc_nanosecs_t
+isc_time_monotonic(void);
+/*%<
+ * Returns the system's monotonic time in linear nanoseconds.
+ */
+
 isc_result_t
 isc_time_now(isc_time_t *t);
 /*%<

lib/isc/time.c

@@ -120,6 +120,18 @@ isc_time_now(isc_time_t *t) {
 	return time_now(t, CLOCKSOURCE);
 }
 
+isc_nanosecs_t
+isc_time_monotonic(void) {
+	struct timespec ts;
+
+	RUNTIME_CHECK(clock_gettime(CLOCK_MONOTONIC, &ts) != -1);
+
+	return (isc_nanosecs_fromtime(((isc_time_t){
+		.seconds = ts.tv_sec,
+		.nanoseconds = ts.tv_nsec,
+	})));
+}
+
 isc_result_t
 isc_time_nowplusinterval(isc_time_t *t, const isc_interval_t *i) {
 	struct timespec ts;