test: hook into PID in tracing tests

This makes sure to NOT hook into other bitcoind binaries run in
paralell in the test framework. We only want to trace the intended
binary.

In interface_usdt_utxocache.py:
While testing the utxocache flush with pruning, bitcoind is
restarted and we need to hook into the new PID again.

test/functional/interface_usdt_net.py

@@ -109,7 +109,7 @@ class NetTracepointTest(BitcoinTestFramework):
 
         self.log.info(
             "hook into the net:inbound_message and net:outbound_message tracepoints")
-        ctx = USDT(path=str(self.options.bitcoind))
+        ctx = USDT(pid=self.nodes[0].process.pid)
         ctx.enable_probe(probe="net:inbound_message",
                          fn_name="trace_inbound_message")
         ctx.enable_probe(probe="net:outbound_message",

test/functional/interface_usdt_utxocache.py

@@ -173,7 +173,7 @@ class UTXOCacheTracepointTest(BitcoinTestFramework):
         invalid_tx.vin[0].prevout.hash = int(block_1_coinbase_txid, 16)
 
         self.log.info("hooking into the utxocache:uncache tracepoint")
-        ctx = USDT(path=str(self.options.bitcoind))
+        ctx = USDT(pid=self.nodes[0].process.pid)
         ctx.enable_probe(probe="utxocache:uncache",
                          fn_name="trace_utxocache_uncache")
         bpf = BPF(text=utxocache_changes_program, usdt_contexts=[ctx], debug=0)
@@ -238,7 +238,7 @@ class UTXOCacheTracepointTest(BitcoinTestFramework):
 
         self.log.info(
             "hook into the utxocache:add and utxocache:spent tracepoints")
-        ctx = USDT(path=str(self.options.bitcoind))
+        ctx = USDT(pid=self.nodes[0].process.pid)
         ctx.enable_probe(probe="utxocache:add", fn_name="trace_utxocache_add")
         ctx.enable_probe(probe="utxocache:spent",
                          fn_name="trace_utxocache_spent")
@@ -334,7 +334,7 @@ class UTXOCacheTracepointTest(BitcoinTestFramework):
 
         self.log.info("test the utxocache:flush tracepoint API")
         self.log.info("hook into the utxocache:flush tracepoint")
-        ctx = USDT(path=str(self.options.bitcoind))
+        ctx = USDT(pid=self.nodes[0].process.pid)
         ctx.enable_probe(probe="utxocache:flush",
                          fn_name="trace_utxocache_flush")
         bpf = BPF(text=utxocache_flushes_program, usdt_contexts=[ctx], debug=0)
@@ -373,6 +373,7 @@ class UTXOCacheTracepointTest(BitcoinTestFramework):
         self.stop_node(0)
 
         bpf.perf_buffer_poll(timeout=200)
+        bpf.cleanup()
 
         self.log.info("check that we don't expect additional flushes")
         assert_equal(0, len(expected_flushes))
@@ -381,6 +382,14 @@ class UTXOCacheTracepointTest(BitcoinTestFramework):
         self.log.info("restart the node with -prune")
         self.start_node(0, ["-fastprune=1", "-prune=1"])
 
+        self.log.info("test the utxocache:flush tracepoint API with pruning")
+        self.log.info("hook into the utxocache:flush tracepoint")
+        ctx = USDT(pid=self.nodes[0].process.pid)
+        ctx.enable_probe(probe="utxocache:flush",
+                         fn_name="trace_utxocache_flush")
+        bpf = BPF(text=utxocache_flushes_program, usdt_contexts=[ctx], debug=0)
+        bpf["utxocache_flush"].open_perf_buffer(handle_utxocache_flush)
+
         BLOCKS_TO_MINE = 350
         self.log.info(f"mine {BLOCKS_TO_MINE} blocks to be able to prune")
         self.generate(self.wallet, BLOCKS_TO_MINE)

test/functional/interface_usdt_validation.py

@@ -94,7 +94,7 @@ class ValidationTracepointTest(BitcoinTestFramework):
         expected_blocks = list()
 
         self.log.info("hook into the validation:block_connected tracepoint")
-        ctx = USDT(path=str(self.options.bitcoind))
+        ctx = USDT(pid=self.nodes[0].process.pid)
         ctx.enable_probe(probe="validation:block_connected",
                          fn_name="trace_block_connected")
         bpf = BPF(text=validation_blockconnected_program,