make tcpv4connect.py example tracer more robust

examples/tracing/tcpv4connect.py

@@ -62,7 +62,7 @@
  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)),