v4.19.13 snapshot.
diff --git a/samples/bpf/trace_output_user.c b/samples/bpf/trace_output_user.c
new file mode 100644
index 0000000..4837d73
--- /dev/null
+++ b/samples/bpf/trace_output_user.c
@@ -0,0 +1,106 @@
+/* This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <linux/perf_event.h>
+#include <linux/bpf.h>
+#include <errno.h>
+#include <assert.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <time.h>
+#include <signal.h>
+#include <libbpf.h>
+#include "bpf_load.h"
+#include "perf-sys.h"
+#include "trace_helpers.h"
+
+static int pmu_fd;
+
+static __u64 time_get_ns(void)
+{
+ struct timespec ts;
+
+ clock_gettime(CLOCK_MONOTONIC, &ts);
+ return ts.tv_sec * 1000000000ull + ts.tv_nsec;
+}
+
+static __u64 start_time;
+
+#define MAX_CNT 100000ll
+
+static int print_bpf_output(void *data, int size)
+{
+ static __u64 cnt;
+ struct {
+ __u64 pid;
+ __u64 cookie;
+ } *e = data;
+
+ if (e->cookie != 0x12345678) {
+ printf("BUG pid %llx cookie %llx sized %d\n",
+ e->pid, e->cookie, size);
+ return LIBBPF_PERF_EVENT_ERROR;
+ }
+
+ cnt++;
+
+ if (cnt == MAX_CNT) {
+ printf("recv %lld events per sec\n",
+ MAX_CNT * 1000000000ll / (time_get_ns() - start_time));
+ return LIBBPF_PERF_EVENT_DONE;
+ }
+
+ return LIBBPF_PERF_EVENT_CONT;
+}
+
+static void test_bpf_perf_event(void)
+{
+ struct perf_event_attr attr = {
+ .sample_type = PERF_SAMPLE_RAW,
+ .type = PERF_TYPE_SOFTWARE,
+ .config = PERF_COUNT_SW_BPF_OUTPUT,
+ };
+ int key = 0;
+
+ pmu_fd = sys_perf_event_open(&attr, -1/*pid*/, 0/*cpu*/, -1/*group_fd*/, 0);
+
+ assert(pmu_fd >= 0);
+ assert(bpf_map_update_elem(map_fd[0], &key, &pmu_fd, BPF_ANY) == 0);
+ ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0);
+}
+
+int main(int argc, char **argv)
+{
+ char filename[256];
+ FILE *f;
+ int ret;
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+
+ test_bpf_perf_event();
+
+ if (perf_event_mmap(pmu_fd) < 0)
+ return 1;
+
+ f = popen("taskset 1 dd if=/dev/zero of=/dev/null", "r");
+ (void) f;
+
+ start_time = time_get_ns();
+ ret = perf_event_poller(pmu_fd, print_bpf_output);
+ kill(0, SIGINT);
+ return ret;
+}