perf test: Provide a subtest callback to ask for the reason for skipping a subtest

Now subtests can inform why a test was skipped. The upcoming patch
improvint PMU event metric testing will use it.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200513212933.41273-1-irogers@google.com
[ split from a larger patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/builtin-test.c

@@ -429,8 +429,15 @@ static int test_and_print(struct test *t, bool force_skip, int subtest)
 	case TEST_OK:
 		pr_info(" Ok\n");
 		break;
-	case TEST_SKIP:
-		color_fprintf(stderr, PERF_COLOR_YELLOW, " Skip\n");
+	case TEST_SKIP: {
+		const char *skip_reason = NULL;
+		if (t->subtest.skip_reason)
+			skip_reason = t->subtest.skip_reason(subtest);
+		if (skip_reason)
+			color_fprintf(stderr, PERF_COLOR_YELLOW, " Skip (%s)\n", skip_reason);
+		else
+			color_fprintf(stderr, PERF_COLOR_YELLOW, " Skip\n");
+	}
 		break;
 	case TEST_FAIL:
 	default:

tools/perf/tests/tests.h

@@ -34,6 +34,7 @@ struct test {
 		bool skip_if_fail;
 		int (*get_nr)(void);
 		const char *(*get_desc)(int subtest);
+		const char *(*skip_reason)(int subtest);
 	} subtest;
 	bool (*is_supported)(void);
 	void *priv;