make tcpv4connect.py example tracer more robust

examples/tracing/tcpv4connect.py

@@ -62,7 +62,7 @@ int kretprobe__tcp_v4_connect(struct pt_regs *ctx)
 	bpf_probe_read(&dport, sizeof(dport), &skp->__sk_common.skc_dport);
 
 	// output
-	bpf_trace_printk("%x %x %d\\n", saddr, daddr, ntohs(dport));
+	bpf_trace_printk("trace_tcp4connect %x %x %d\\n", saddr, daddr, ntohs(dport));
 
 	currsock.delete(&pid);
 
@@ -86,10 +86,19 @@ def inet_ntoa(addr):
 		addr = addr >> 8
 	return dq
 
-# format output
+# filter and format output
 while 1:
-	(task, pid, cpu, flags, ts, msg) = b.trace_fields()
-	(saddr_hs, daddr_hs, dport_s) = msg.split(" ")
+        # Read messages from kernel pipe
+        try:
+            (task, pid, cpu, flags, ts, msg) = b.trace_fields()
+            (_tag, saddr_hs, daddr_hs, dport_s) = msg.split(" ")
+        except ValueError:
+            # Ignore messages from other tracers
+            continue
+
+        # Ignore messages from other tracers
+        if _tag != "trace_tcp4connect":
+            continue
 
 	print("%-6d %-12.12s %-16s %-16s %-4s" % (pid, task,
 	    inet_ntoa(int(saddr_hs, 16)),