lib: Magic for_each_engine() macro to iterate over available engines

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

lib/igt_gt.h

@@ -100,4 +100,13 @@ extern const struct intel_execution_engine {
 	unsigned flags;
 } intel_execution_engines[];
 
+#define for_if(expr__) if (!(expr__)) {} else
+
+#define for_each_engine(fd__, flags__) \
+	for (const struct intel_execution_engine *e__ = intel_execution_engines;\
+	     e__->name; \
+	     e__++) \
+		for_if (gem_has_ring(fd, flags__ = e__->exec_id | e__->flags))
+
+
 #endif /* IGT_GT_H */