Update trace perf output with struct deserialize example

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

examples/tracing/trace_perf_output.py

@@ -8,20 +8,28 @@
 
 import atexit
 from bcc import BPF
-import ctypes
+import ctypes as ct
+
+class Data(ct.Structure):
+    _fields_ = [("ts", ct.c_ulonglong),
+                ("magic", ct.c_ulonglong)]
 
 counter = 0
 def cb(cpu, data, size):
+    assert size >= ct.sizeof(Data)
+    event = ct.cast(data, ct.POINTER(Data)).contents
+    print("[%0d] %f: %x" % (cpu, float(event.ts) / 1000000, event.magic))
     global counter
     counter += 1
 
 prog = """
 BPF_PERF_OUTPUT(events);
 BPF_TABLE("array", int, u64, counters, 10);
-int kprobe__sys_write(void *ctx) {
+int kprobe__sys_clone(void *ctx) {
   struct {
     u64 ts;
-  } data = {bpf_ktime_get_ns()};
+    u64 magic;
+  } data = {bpf_ktime_get_ns(), 0x12345678};
   int rc;
   if ((rc = events.perf_submit(ctx, &data, sizeof(data))) < 0)
     bpf_trace_printk("perf_output failed: %d\\n", rc);
@@ -38,7 +46,7 @@ b["events"].open_perf_buffer(cb)
 def print_counter():
     global counter
     global b
-    print("counter = %d vs %d" % (counter, b["counters"][ctypes.c_int(0)].value))
+    print("counter = %d vs %d" % (counter, b["counters"][ct.c_int(0)].value))
 
 print("Tracing sys_write, try `dd if=/dev/zero of=/dev/null`")
 print("Tracing... Hit Ctrl-C to end.")