shared: add nm_utils_clock_gettime_*() util

Using clock_gettime() directly is a bit inconvenient. We usually
want to combine the fields of struct timespec into one timestamp
(for example, in unit nanoseconds).

Add a helper function to do that.

shared/nm-glib-aux/nm-time-utils.c

@@ -273,3 +273,23 @@ nm_utils_monotonic_timestamp_as_boottime (gint64 timestamp, gint64 timestamp_ns_
 
 	return timestamp - offset;
 }
+
+gint64
+nm_utils_clock_gettime_ns (clockid_t clockid)
+{
+	struct timespec tp;
+
+	if (clock_gettime (clockid, &tp) != 0)
+		return -NM_ERRNO_NATIVE (errno);
+	return nm_utils_timespec_to_ns (&tp);
+}
+
+gint64
+nm_utils_clock_gettime_ms (clockid_t clockid)
+{
+	struct timespec tp;
+
+	if (clock_gettime (clockid, &tp) != 0)
+		return -NM_ERRNO_NATIVE (errno);
+	return nm_utils_timespec_to_ms (&tp);
+}

shared/nm-glib-aux/nm-time-utils.h

@@ -21,6 +21,22 @@
 #ifndef __NM_TIME_UTILS_H__
 #define __NM_TIME_UTILS_H__
 
+#include <time.h>
+
+static inline gint64
+nm_utils_timespec_to_ns (const struct timespec *ts)
+{
+	return   (((gint64) ts->tv_sec) * ((gint64) NM_UTILS_NS_PER_SECOND))
+	       +  ((gint64) ts->tv_nsec);
+}
+
+static inline gint64
+nm_utils_timespec_to_ms (const struct timespec *ts)
+{
+	return   (((gint64) ts->tv_sec)  * ((gint64) 1000))
+	       + (((gint64) ts->tv_nsec) / ((gint64) NM_UTILS_NS_PER_SECOND / 1000));
+}
+
 gint64 nm_utils_get_monotonic_timestamp_ns (void);
 gint64 nm_utils_get_monotonic_timestamp_us (void);
 gint64 nm_utils_get_monotonic_timestamp_ms (void);
@@ -34,4 +50,7 @@ nm_utils_get_monotonic_timestamp_ns_cached (gint64 *cache_now)
 	       ?: (*cache_now = nm_utils_get_monotonic_timestamp_ns ());
 }
 
+gint64 nm_utils_clock_gettime_ns (clockid_t clockid);
+gint64 nm_utils_clock_gettime_ms (clockid_t clockid);
+
 #endif /* __NM_TIME_UTILS_H__ */