bpf: add a test case for helper bpf_perf_prog_read_value

The bpf sample program trace_event is enhanced to use the new
helper to print out enabled/running time.

Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
index 7bd827b..bf4f1b6 100644
--- a/samples/bpf/trace_event_user.c
+++ b/samples/bpf/trace_event_user.c
@@ -127,6 +127,9 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
 	int *pmu_fd = malloc(nr_cpus * sizeof(int));
 	int i, error = 0;
 
+	/* system wide perf event, no need to inherit */
+	attr->inherit = 0;
+
 	/* open perf_event on all cpus */
 	for (i = 0; i < nr_cpus; i++) {
 		pmu_fd[i] = sys_perf_event_open(attr, -1, i, -1, 0);
@@ -154,6 +157,11 @@ static void test_perf_event_task(struct perf_event_attr *attr)
 {
 	int pmu_fd;
 
+	/* per task perf event, enable inherit so the "dd ..." command can be traced properly.
+	 * Enabling inherit will cause bpf_perf_prog_read_time helper failure.
+	 */
+	attr->inherit = 1;
+
 	/* open task bound event */
 	pmu_fd = sys_perf_event_open(attr, 0, -1, -1, 0);
 	if (pmu_fd < 0) {
@@ -175,14 +183,12 @@ static void test_bpf_perf_event(void)
 		.freq = 1,
 		.type = PERF_TYPE_HARDWARE,
 		.config = PERF_COUNT_HW_CPU_CYCLES,
-		.inherit = 1,
 	};
 	struct perf_event_attr attr_type_sw = {
 		.sample_freq = SAMPLE_FREQ,
 		.freq = 1,
 		.type = PERF_TYPE_SOFTWARE,
 		.config = PERF_COUNT_SW_CPU_CLOCK,
-		.inherit = 1,
 	};
 	struct perf_event_attr attr_hw_cache_l1d = {
 		.sample_freq = SAMPLE_FREQ,
@@ -192,7 +198,6 @@ static void test_bpf_perf_event(void)
 			PERF_COUNT_HW_CACHE_L1D |
 			(PERF_COUNT_HW_CACHE_OP_READ << 8) |
 			(PERF_COUNT_HW_CACHE_RESULT_ACCESS << 16),
-		.inherit = 1,
 	};
 	struct perf_event_attr attr_hw_cache_branch_miss = {
 		.sample_freq = SAMPLE_FREQ,
@@ -202,7 +207,6 @@ static void test_bpf_perf_event(void)
 			PERF_COUNT_HW_CACHE_BPU |
 			(PERF_COUNT_HW_CACHE_OP_READ << 8) |
 			(PERF_COUNT_HW_CACHE_RESULT_MISS << 16),
-		.inherit = 1,
 	};
 	struct perf_event_attr attr_type_raw = {
 		.sample_freq = SAMPLE_FREQ,
@@ -210,7 +214,6 @@ static void test_bpf_perf_event(void)
 		.type = PERF_TYPE_RAW,
 		/* Intel Instruction Retired */
 		.config = 0xc0,
-		.inherit = 1,
 	};
 
 	printf("Test HW_CPU_CYCLES\n");