IO: Add current_time_now() function for immediate timestamp

Add a current_time_now() function which gets an immediate monotonic
timestamp instead of using the cached value from the event loop. This is
useful for callers that need precise times, such as the Babel RTT
measurement code.

Minor changes by committer.

sysdep/unix/io.c

@@ -171,6 +171,19 @@ times_update_real_time(struct timeloop *loop)
   loop->real_time = ts.tv_sec S + ts.tv_nsec NS;
 }
 
+btime
+current_time_now(void)
+{
+  struct timespec ts;
+  int rv;
+
+  rv = clock_gettime(CLOCK_MONOTONIC, &ts);
+  if (rv < 0)
+    die("clock_gettime: %m");
+
+  return ts.tv_sec S + ts.tv_nsec NS;
+}
+
 
 /**
  * DOC: Sockets