Add ddir_rw_sum()

We sum up the three data direction primitives a lot, this is
more readable.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/io_ddir.h b/io_ddir.h
index fa3b143..df5abbb 100644
--- a/io_ddir.h
+++ b/io_ddir.h
@@ -45,4 +45,7 @@
 
 #define ddir_trim(ddir) ((ddir) == DDIR_TRIM)
 
+#define ddir_rw_sum(arr)	\
+	((arr)[DDIR_READ] + (arr)[DDIR_WRITE] + (arr)[DDIR_TRIM])
+
 #endif