samples/bpf: Check the result of system()

To avoid the below build warning message,
use new generate_load() checking the return value.

  ignoring return value of ‘system’, declared with attribute warn_unused_result

And it also refactors the duplicate code of both
test_perf_event_all_cpu() and test_perf_event_task()

Cc: Teng Qin <qinteng@fb.com>
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
index 1fa1becfa641510ae67db4d0ea64c3971f6d2f4d..d08046ab81f043505e0ea42a2e8c85661ae68f76 100644 (file)
--- a/samples/bpf/trace_event_user.c
+++ b/samples/bpf/trace_event_user.c
@@ -122,6 +122,16 @@ static void print_stacks(void)
        }
 }
 
+static inline int generate_load(void)
+{
+       if (system("dd if=/dev/zero of=/dev/null count=5000k status=none") < 0) {
+               printf("failed to generate some load with dd: %s\n", strerror(errno));
+               return -1;
+       }
+
+       return 0;
+}
+
 static void test_perf_event_all_cpu(struct perf_event_attr *attr)
 {
        int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
@@ -142,7 +152,11 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
                assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_SET_BPF, prog_fd[0]) == 0);
                assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_ENABLE) == 0);
        }
-       system("dd if=/dev/zero of=/dev/null count=5000k status=none");
+
+       if (generate_load() < 0) {
+               error = 1;
+               goto all_cpu_err;
+       }
        print_stacks();
 all_cpu_err:
        for (i--; i >= 0; i--) {
@@ -156,7 +170,7 @@ all_cpu_err:
 
 static void test_perf_event_task(struct perf_event_attr *attr)
 {
-       int pmu_fd;
+       int pmu_fd, error = 0;
 
        /* 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.
@@ -171,10 +185,17 @@ static void test_perf_event_task(struct perf_event_attr *attr)
        }
        assert(ioctl(pmu_fd, PERF_EVENT_IOC_SET_BPF, prog_fd[0]) == 0);
        assert(ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE) == 0);
-       system("dd if=/dev/zero of=/dev/null count=5000k status=none");
+
+       if (generate_load() < 0) {
+               error = 1;
+               goto err;
+       }
        print_stacks();
+err:
        ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
        close(pmu_fd);
+       if (error)
+               int_exit(0);
 }
 
 static void test_bpf_perf_event(void)