[PATCH v2 1/3] iotests: run the test pool with the 'fork' start method

["Denis V. Lunev" <den@openvz.org>]

run_tests_pool() shares the runner via the class attribute
TestRunner.shared_self, relying on worker processes to inherit it.
That only works with the 'fork' start method. Python 3.14 switched
the Linux default to 'forkserver', so workers see shared_self as
None and parallel runs abort with:

  assert runner is not None
  AssertionError

Only reproduces with Python 3.14+ and 'check -jN' (N > 1); meson
runs one test per process and never calls run_tests_pool(), so CI
is unaffected.

Request get_context('fork') explicitly; it is available on all
supported Python versions and a no-op before 3.14.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Hanna Reitz <hreitz@redhat.com>
---
 tests/qemu-iotests/testrunner.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/testrunner.py b/tests/qemu-iotests/testrunner.py
index dbe2dddc32..cc36867719 100644
--- a/tests/qemu-iotests/testrunner.py
+++ b/tests/qemu-iotests/testrunner.py
@@ -26,7 +26,7 @@
 import json
 import shutil
 import sys
-from multiprocessing import Pool
+from multiprocessing import get_context
 from typing import List, Optional, Any, Sequence, Dict
 from testenv import TestEnv
 
@@ -125,7 +125,7 @@ def run_tests_pool(self, tests: List[str],
         assert TestRunner.shared_self is None
         TestRunner.shared_self = self
 
-        with Pool(jobs) as p:
+        with get_context('fork').Pool(jobs) as p:
             results = p.starmap(self.proc_run_test,
                                 zip(tests, [test_field_width] * len(tests)))
 
-- 
2.53.0