Modify the code according to chenhengqi's suggestion

No more support timestamp and COMM, procedure as follows:
1. startup UNIX socket server:
```bash
[rongtao@bogon ~]$ nc --unixsock ./unix-sock -l
```
2. start UNIX socket client:
```bash
[rongtao@bogon ~]$ nc --unixsock ./unix-sock
```
3. startup undump.py script
```
[rongtao@bogon study]$ sudo ./undump2.py -p 41147
Tracing PID=41147 UNIX socket packets ... Hit Ctrl-C to end
```
4. send some packets
```
[rongtao@bogon ~]$ nc --unixsock ./unix-sock
abcdefg
1234567890
```

5. capture these packets
server recv:
```
[rongtao@bogon ~]$ nc --unixsock ./unix-sock -l
abcdefg
1234567890
```
undump.py capture
```
[rongtao@bogon study]$ sudo ./undump2.py -p 41147
Tracing PID=41147 UNIX socket packets ... Hit Ctrl-C to end
PID 41147 Recv 8 bytes
    61 62 63 64 65 66 67 0a 
PID 41147 Recv 11 bytes
    31 32 33 34 35 36 37 38 39 30 0a
```

examples/tracing/undump.py

@@ -12,6 +12,8 @@
 # Licensed under the GPL License, Version 2.0
 #
 # 27-Aug-2021 Rong Tao Created this.
+# 17-Sep-2021 Rong Tao Simplify according to chenhengqi's suggestion
+# https://github.com/iovisor/bcc/pull/3615
 #
 from __future__ import print_function
 from bcc import BPF
@@ -27,16 +29,13 @@
 # arguments
 examples = """examples:
  ./undump # trace/dump all UNIX packets
- ./undump -t # include timestamps
  ./undump -p 181 # only trace/dump PID 181
 """
 parser = argparse.ArgumentParser(
  description="Dump UNIX socket packets",
  formatter_class=argparse.RawDescriptionHelpFormatter,
  epilog=examples)
 
-parser.add_argument("-t", "--timestamp", 
- action="store_true", help="include timestamp on output")
 parser.add_argument("-p", "--pid",
  help="trace this PID only")
 args = parser.parse_args()
@@ -55,66 +54,17 @@
 #include <net/sock.h>
 #include <net/af_unix.h>
 
-// separate data structs for ipv4 and ipv6
-struct stream_data_t {
- u64 ts_us;
- u32 pid;
- u32 uid;
- u32 sock_state;
- u32 sock_type; //type of socket[STREAM|DRGMA]
- u64 sock_flags;
- char task[TASK_COMM_LEN];
- char *unix_sock_path;
- int msg_namelen;
-};
-BPF_PERF_OUTPUT(stream_recvmsg_events);
-
 #define MAX_PKT 512
 struct recv_data_t {
  u32 recv_len;
  u8 pkt[MAX_PKT];
 };
 
 // single element per-cpu array to hold the current event off the stack
-BPF_PERCPU_ARRAY(unix_data, struct recv_data_t,1);
+BPF_PERCPU_ARRAY(unix_data, struct recv_data_t, 1);
 
 BPF_PERF_OUTPUT(unix_recv_events);
 
-//static int unix_stream_recvmsg(struct socket *sock, struct msghdr *msg,
-// size_t size, int flags)
-int trace_stream_entry(struct pt_regs *ctx)
-{
- int ret = PT_REGS_RC(ctx);
- 
- u64 pid_tgid = bpf_get_current_pid_tgid();
- u32 pid = pid_tgid >> 32;
- u32 tid = pid_tgid;
-
- FILTER_PID
-
- struct stream_data_t data4 = {.pid = pid,};
- data4.uid = bpf_get_current_uid_gid();
- data4.ts_us = bpf_ktime_get_ns() / 1000;
-
- struct socket *sock = (struct socket *)PT_REGS_PARM1(ctx); 
- struct msghdr *msg = (struct msghdr *)PT_REGS_PARM2(ctx); 
-
- data4.sock_state = sock->state;
- data4.sock_type = sock->type;
- data4.sock_flags = sock->flags;
-
- data4.msg_namelen = msg->msg_namelen;
- 
- bpf_get_current_comm(&data4.task, sizeof(data4.task));
- 
- struct unix_sock *unsock = (struct unix_sock *)sock->sk;
- data4.unix_sock_path = (char *)unsock->path.dentry->d_name.name;
- 
- stream_recvmsg_events.perf_submit(ctx, &data4, sizeof(data4));
-
- return 0;
-};
-
 int trace_unix_stream_read_actor(struct pt_regs *ctx)
 {
  u32 zero = 0;
@@ -151,50 +101,38 @@
 
 bpf_text = bpf_text.replace('FILTER_PID', '')
 
-# process event
-def print_stream_event(cpu, data, size):
- event = b["stream_recvmsg_events"].event(data)
- global start_ts
- if args.timestamp:
- if start_ts == 0:
- start_ts = event.ts_us
- printb(b"%-9.3f" % ((float(event.ts_us) - start_ts) / 1000000), nl="")
- printb(b"%-6s %-12s" % (event.pid, event.task))
-
 # process event
 def print_recv_pkg(cpu, data, size):
  event = b["unix_recv_events"].event(data)
- print("----------------", end="")
+ if args.pid:
+ print("PID \033[1;31m%s\033[m " % args.pid, end="")
+ print("Recv \033[1;31m%d\033[m bytes" % event.recv_len)
+
+ print(" ", end="")
  for i in range(0, event.recv_len):
  print("%02x " % event.pkt[i], end="")
  sys.stdout.flush()
  if (i+1)%16 == 0:
  print("")
- print("----------------", end="")
- print("\n----------------recv %d bytes" % event.recv_len)
- 
+ print(" ", end="")
+ print("")
+
 # initialize BPF
 b = BPF(text=bpf_text)
-b.attach_kprobe(event="unix_stream_recvmsg", fn_name="trace_stream_entry")
 b.attach_kprobe(event="unix_stream_read_actor", fn_name="trace_unix_stream_read_actor")
 
-print("Tracing UNIX socket packets ... Hit Ctrl-C to end")
-
-# header
-if args.timestamp:
- print("%-9s" % ("TIME(s)"), end="")
-
-print("%-6s %-12s" % ("PID", "COMM"), end="")
+if args.pid:
+ print("Tracing \033[1;31mPID=%s\033[m UNIX socket packets ... Hit Ctrl-C to end" % args.pid)
+else:
+ print("Tracing UNIX socket packets ... Hit Ctrl-C to end")
 
 start_ts = 0
 
 # read events
-b["stream_recvmsg_events"].open_perf_buffer(print_stream_event)
 b["unix_recv_events"].open_perf_buffer(print_recv_pkg)
 
 while True:
  try:
  b.perf_buffer_poll()
  except KeyboardInterrupt:
  exit()
-