tests: teach runtime runner about multiple before clauses

As noted in bpftrace#2402, usdt flakiness was made better by
508538a but not fully fixed.

This commit is what I should have done all along: it allows the test
runner to parse and wait for multiple BEFORE clauses and thus ensures
the processes have started before the test runs.

There are two minor changes:

  1. The check for child processes is now `ps --ppid` based to
     eventually allow parallel process runs in the same environment.
  2. Because of the `ps` usage, the name check is now truncated to 15
     chars, which will fail if TASK_COMM_LEN is not 16. That looks like
     a constant in the kernel, so I think we're good.

tests/runtime/engine/parser.py

@@ -25,7 +25,7 @@ class InvalidFieldError(Exception):
         'prog',
         'expect',
         'timeout',
-        'before',
+        'befores',
         'after',
         'suite',
         'kernel_min',
@@ -101,7 +101,7 @@ def __read_test_struct(test, test_suite):
         prog = ''
         expect = ''
         timeout = ''
-        before = ''
+        befores = []
         after = ''
         kernel_min = ''
         kernel_max = ''
@@ -128,7 +128,7 @@ def __read_test_struct(test, test_suite):
             elif item_name == 'TIMEOUT':
                 timeout = int(line.strip(' '))
             elif item_name == 'BEFORE':
-                before = line
+                befores.append(line)
             elif item_name == 'AFTER':
                 after = line
             elif item_name == 'MIN_KERNEL':
@@ -193,7 +193,7 @@ def __read_test_struct(test, test_suite):
             prog,
             expect,
             timeout,
-            before,
+            befores,
             after,
             test_suite,
             kernel_min,

tests/runtime/engine/runner.py

@@ -158,7 +158,8 @@ def run_test(test):
         signal.signal(signal.SIGALRM, Runner.__handler)
 
         p = None
-        before = None
+        befores = []
+        child_name = None
         bpftrace = None
         after = None
         try:
@@ -195,22 +196,42 @@ def run_test(test):
                         print(warn("[   SKIP   ] ") + "%s.%s" % (test.suite, test.name))
                         return Runner.SKIP_FEATURE_REQUIREMENT_UNSATISFIED
 
-            if test.before:
-                before = subprocess.Popen(test.before, shell=True, preexec_fn=os.setsid)
-                waited=0
+            if test.befores:
+                for before in test.befores:
+                    before = subprocess.Popen(before, shell=True, preexec_fn=os.setsid)
+                    befores.append(before)
+
                 with open(devnull, 'w') as dn:
-                    # This might not work for complicated cases, such as if
-                    # a test program needs to accept arguments. It covers the
-                    # current simple calls with no arguments
-                    child_name = os.path.basename(test.before.split()[-1])
-                    while subprocess.call(["pidof", child_name], stdout=dn, stderr=dn) != 0:
+                    child_names = [os.path.basename(x.strip().split()[-1]) for x in test.befores]
+                    child_names = sorted((x[:15] for x in child_names))  # cut to comm length
+
+                    # Print the names of all of our children and look
+                    # for the ones from BEFORE clauses
+                    waited=0
+                    while waited <= test.timeout:
+                        children = subprocess.run(["ps", "--ppid", str(os.getpid()), "--no-headers", "-o", "comm"],
+                                                  check=False,
+                                                  capture_output=True)
+                        if children.returncode == 0 and children.stdout:
+                            lines = [line.decode('utf-8') for line in children.stdout.splitlines()]
+                            lines = sorted((line.strip() for line in lines if line != 'ps'))
+                            if lines == child_names:
+                                break
+
                         time.sleep(0.1)
                         waited+=0.1
-                        if waited > test.timeout:
-                            raise TimeoutError('Timed out waiting for BEFORE %s ', test.before)
+
+                    if waited > test.timeout:
+                        raise TimeoutError(f'Timed out waiting for BEFORE(s) {test.befores}')
 
             bpf_call = Runner.prepare_bpf_call(test)
-            if test.before and '{{BEFORE_PID}}' in bpf_call:
+            if test.befores and '{{BEFORE_PID}}' in bpf_call:
+                if len(test.befores) > 1:
+                    raise ValueError(f"test has {len(test.befores)} BEFORE clauses but BEFORE_PID usage requires exactly one")
+
+                child_name = test.befores[0].strip().split()[-1]
+                child_name = os.path.basename(child_name)
+
                 childpid = subprocess.Popen(["pidof", child_name], stdout=subprocess.PIPE, universal_newlines=True).communicate()[0].split()[0]
                 bpf_call = re.sub("{{BEFORE_PID}}", str(childpid), bpf_call)
             env = {
@@ -275,8 +296,10 @@ def run_test(test):
                 print('\tCurrent output: %s' % output)
                 return Runner.TIMEOUT
         finally:
-            if before and before.poll() is None:
-                os.killpg(os.getpgid(before.pid), signal.SIGKILL)
+            if befores:
+                for before in befores:
+                    if before.poll() is None:
+                        os.killpg(os.getpgid(before.pid), signal.SIGKILL)
 
             if bpftrace and bpftrace.poll() is None:
                 os.killpg(os.getpgid(p.pid), signal.SIGKILL)

tests/runtime/usdt

@@ -240,7 +240,8 @@ NAME "usdt probes - file based semaphore activation multi process"
 RUN {{BPFTRACE}} runtime/scripts/usdt_file_activation_multiprocess.bt --usdt-file-activation
 EXPECT found 2 processes
 TIMEOUT 5
-BEFORE ./testprogs/two_usdt_semaphore_tests
+BEFORE ./testprogs/usdt_semaphore_test
+BEFORE ./testprogs/usdt_semaphore_test
 REQUIRES ./testprogs/usdt_semaphore_test should_not_skip
 
 NAME "usdt probes - list probes by pid in separate mountns"