lib: (somewhat) structured logging support

Apparently there's a bit a need for more verbose output in testcases,
mostly for debugging purposes. At least gem_reset_stats and pm_rps
have a verbose mode.

On top of that we're currently not taking advantage of piglit's "warn"
state all that much. But I think it might be useful for testcases which
are notorious for some kinds of spurious failures, like e.g. the really
nasty timing checks in kms_flip. If we demote some of them to just
warnings we could run the overall tests more often.

Hence this patchs adds a new igt_log function with the three levels DEBUG,
INFO and WARN. Plus a bunch of convenience helpers to keep the test
code tidy.

The level can be set through an enviroment vairable IGT_LOG_LEVEL with
info being the default. Also tests can look at the selected log level in
case they want to run costly debug functions only when needed.

Comments highly welcome, I plan to roll this out over tests which can
use it (not all, imo that's too much churn) once we've settled on the
interfaces/semantics.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lib/drmtest.h

@@ -294,6 +294,33 @@ void igt_wait_helper(struct igt_helper_process *proc);
 #define igt_fork_helper(proc) \
 	for (; __igt_fork_helper(proc); exit(0))
 
+/* logging support */
+enum igt_log_level {
+	IGT_LOG_DEBUG,
+	IGT_LOG_INFO,
+	IGT_LOG_WARN,
+	IGT_LOG_NONE,
+};
+__attribute__((format(printf, 2, 3)))
+void igt_log(enum igt_log_level level, const char *format, ...);
+#define igt_debug(f...) igt_log(IGT_LOG_DEBUG, f)
+#define igt_info(f...) igt_log(IGT_LOG_INFO, f)
+#define igt_warn(f...) igt_log(IGT_LOG_WARN, f)
+extern enum igt_log_level igt_log_level;
+
+#define igt_warn_on(condition) do {\
+		if (condition) \
+			igt_warn("Warning on condition %s in fucntion %s, file %s:%i\n", \
+				 #condition, __func__, __FILE__, __LINE__); \
+	} while (0)
+#define igt_warn_on_f(condition, f...) do {\
+		if (condition) {\
+			igt_warn("Warning on condition %s in fucntion %s, file %s:%i\n", \
+				 #condition, __func__, __FILE__, __LINE__); \
+			igt_warn(f); \
+		} \
+	} while (0)
+
 /* check functions which auto-skip tests by calling igt_skip() */
 void gem_require_caching(int fd);
 static inline void gem_require_ring(int fd, int ring_id)