Add time_since_genesis()

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/time.c b/time.c
index f3de3e7..b145dc5 100644
--- a/time.c
+++ b/time.c
@@ -53,6 +53,11 @@
 	} while (!td->terminate);
 }
 
+uint64_t time_since_genesis(void)
+{
+	return time_since_now(&genesis);
+}
+
 uint64_t mtime_since_genesis(void)
 {
 	return mtime_since_now(&genesis);