bcc: Add test for tracepoint support

The test asserts that we can enable the sched_switch tracepoint and read
some events from it. The test is also marked to require kernel 4.7 or
later, because that's where the BPF support for tracepoints was introduced.

tests/python/CMakeLists.txt

@@ -50,6 +50,8 @@ add_test(NAME py_uprobes WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
   COMMAND ${TEST_WRAPPER} py_uprobes sudo ${CMAKE_CURRENT_SOURCE_DIR}/test_uprobes.py)
 add_test(NAME py_test_stackid WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
   COMMAND ${TEST_WRAPPER} py_stackid sudo ${CMAKE_CURRENT_SOURCE_DIR}/test_stackid.py)
+add_test(NAME py_test_tracepoint WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+  COMMAND ${TEST_WRAPPER} py_test_tracepoint sudo ${CMAKE_CURRENT_SOURCE_DIR}/test_tracepoint.py)
 
 add_test(NAME py_test_dump_func WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
   COMMAND ${TEST_WRAPPER} py_dump_func simple ${CMAKE_CURRENT_SOURCE_DIR}/test_dump_func.py)

tests/python/test_tracepoint.py

+#!/usr/bin/env python
+# Copyright (c) Sasha Goldshtein
+# Licensed under the Apache License, Version 2.0 (the "License")
+
+import bcc
+import unittest
+from time import sleep
+import distutils.version
+import os
+
+def kernel_version_ge(major, minor):
+    # True if running kernel is >= X.Y
+    version = distutils.version.LooseVersion(os.uname()[2]).version
+    if version[0] > major:
+        return True
+    if version[0] < major:
+        return False
+    if minor and version[1] < minor:
+        return False
+    return True
+
+@unittest.skipUnless(kernel_version_ge(4,7), "requires kernel >= 4.7")
+class TestTracepoint(unittest.TestCase):
+    def test_tracepoint(self):
+        text = """#include <linux/ptrace.h>
+        struct tp_args {
+            unsigned long long __unused__;
+            char prev_comm[16];
+            pid_t prev_pid;
+            int prev_prio;
+            long prev_state;
+            char next_comm[16];
+            pid_t next_pid;
+            int next_prio;
+        };
+        BPF_HASH(switches, u32, u64);
+        int probe_switch(struct tp_args *args) {
+            if (args == 0)
+                return 0;
+            u64 val = 0;
+            u32 pid = args->next_pid;
+            u64 *existing = switches.lookup_or_init(&pid, &val);
+            (*existing)++;
+            return 0;
+        }
+        """
+        b = bcc.BPF(text=text)
+        b.attach_tracepoint("sched:sched_switch", "probe_switch")
+        sleep(1)
+        total_switches = 0
+        for k, v in b["switches"].items():
+            total_switches += v.value
+        self.assertNotEqual(0, total_switches)
+        b.detach_tracepoint("sched:sched_switch")
+
+if __name__ == "__main__":
+    unittest.main()