tracing: use bitcoind pid in bcc tracing examples

BCC needs the PID of a bitcoind process to attach to the tracepoints
(instead of the binary path used before) when the tracepoints have a
semaphore.

For reference, we already use the PID in our tracepoint interface
tests. See 220a5a2841.

contrib/tracing/README.md

@@ -82,7 +82,7 @@ about the connection. Peers can be selected individually to view recent P2P
 messages.
 
 ```
-$ python3 contrib/tracing/p2p_monitor.py ./build/src/bitcoind
+$ python3 contrib/tracing/p2p_monitor.py $(pidof bitcoind)
 ```
 
 Lists selectable peers and traffic and connection information.
@@ -150,7 +150,7 @@ lost. BCC prints: `Possibly lost 2 samples` on lost messages.
 
 
 ```
-$ python3 contrib/tracing/log_raw_p2p_msgs.py ./build/src/bitcoind
+$ python3 contrib/tracing/log_raw_p2p_msgs.py $(pidof bitcoind)
 ```
 
 ```
@@ -241,7 +241,7 @@ A BCC Python script to log the UTXO cache flushes. Based on the
 `utxocache:flush` tracepoint.
 
 ```bash
-$ python3 contrib/tracing/log_utxocache_flush.py ./build/src/bitcoind
+$ python3 contrib/tracing/log_utxocache_flush.py $(pidof bitcoind)
 ```
 
 ```
@@ -300,7 +300,7 @@ comprising a timestamp along with all event data available via the event's
 tracepoint.
 
 ```console
-$ python3 contrib/tracing/mempool_monitor.py ./build/src/bitcoind
+$ python3 contrib/tracing/mempool_monitor.py $(pidof bitcoind)
 ```
 
 ```

contrib/tracing/log_raw_p2p_msgs.py

@@ -132,8 +132,9 @@ def print_message(event, inbound):
           )
 
 
-def main(bitcoind_path):
-    bitcoind_with_usdts = USDT(path=str(bitcoind_path))
+def main(pid):
+    print(f"Hooking into bitcoind with pid {pid}")
+    bitcoind_with_usdts = USDT(pid=int(pid))
 
     # attaching the trace functions defined in the BPF program to the tracepoints
     bitcoind_with_usdts.enable_probe(
@@ -176,8 +177,8 @@ def main(bitcoind_path):
 
 
 if __name__ == "__main__":
-    if len(sys.argv) < 2:
-        print("USAGE:", sys.argv[0], "path/to/bitcoind")
+    if len(sys.argv) != 2:
+        print("USAGE:", sys.argv[0], "<pid of bitcoind>")
         exit()
-    path = sys.argv[1]
-    main(path)
+    pid = sys.argv[1]
+    main(pid)

contrib/tracing/log_utxocache_flush.py

@@ -70,8 +70,9 @@ def print_event(event):
     ))
 
 
-def main(bitcoind_path):
-    bitcoind_with_usdts = USDT(path=str(bitcoind_path))
+def main(pid):
+    print(f"Hooking into bitcoind with pid {pid}")
+    bitcoind_with_usdts = USDT(pid=int(pid))
 
     # attaching the trace functions defined in the BPF program
     # to the tracepoints
@@ -99,9 +100,9 @@ def main(bitcoind_path):
 
 
 if __name__ == "__main__":
-    if len(sys.argv) < 2:
-        print("USAGE: ", sys.argv[0], "path/to/bitcoind")
+    if len(sys.argv) != 2:
+        print("USAGE: ", sys.argv[0], "<pid of bitcoind>")
         exit(1)
 
-    path = sys.argv[1]
-    main(path)
+    pid = sys.argv[1]
+    main(pid)

contrib/tracing/mempool_monitor.py

@@ -114,8 +114,9 @@ int trace_replaced(struct pt_regs *ctx) {
 """
 
 
-def main(bitcoind_path):
-    bitcoind_with_usdts = USDT(path=str(bitcoind_path))
+def main(pid):
+    print(f"Hooking into bitcoind with pid {pid}")
+    bitcoind_with_usdts = USDT(pid=int(pid))
 
     # attaching the trace functions defined in the BPF program
     # to the tracepoints
@@ -365,8 +366,8 @@ class Dashboard:
 
 if __name__ == "__main__":
     if len(sys.argv) < 2:
-        print("USAGE: ", sys.argv[0], "path/to/bitcoind")
+        print("USAGE: ", sys.argv[0], "<pid of bitcoind>")
         exit(1)
 
-    path = sys.argv[1]
-    main(path)
+    pid = sys.argv[1]
+    main(pid)

contrib/tracing/p2p_monitor.py

@@ -14,8 +14,9 @@
 # outbound P2P messages. The eBPF program submits the P2P messages to
 # this script via a BPF ring buffer.
 
-import sys
 import curses
+import os
+import sys
 from curses import wrapper, panel
 from bcc import BPF, USDT
 
@@ -115,10 +116,10 @@ class Peer:
             self.total_outbound_msgs += 1
 
 
-def main(bitcoind_path):
+def main(pid):
     peers = dict()
-
-    bitcoind_with_usdts = USDT(path=str(bitcoind_path))
+    print(f"Hooking into bitcoind with pid {pid}")
+    bitcoind_with_usdts = USDT(pid=int(pid))
 
     # attaching the trace functions defined in the BPF program to the tracepoints
     bitcoind_with_usdts.enable_probe(
@@ -245,9 +246,14 @@ def render(screen, peers, cur_list_pos, scroll, ROWS_AVALIABLE_FOR_LIST, info_pa
                         (msg.msg_type, msg.size), curses.A_NORMAL)
 
 
+def running_as_root():
+    return os.getuid() == 0
+
 if __name__ == "__main__":
-    if len(sys.argv) < 2:
-        print("USAGE:", sys.argv[0], "path/to/bitcoind")
+    if len(sys.argv) != 2:
+        print("USAGE:", sys.argv[0], "<pid of bitcoind>")
         exit()
-    path = sys.argv[1]
-    main(path)
+    if not running_as_root():
+        print("You might not have the privileges required to hook into the tracepoints!")
+    pid = sys.argv[1]
+    main(pid)