[Buildroot] [PATCH 1/1] support/testing: transfer config in environment instead of class variables

* [Buildroot] [PATCH 1/1] support/testing: transfer config in environment instead of class variables
@ 2026-02-27 19:21 Fiona Klute via buildroot
  2026-02-28 19:50 ` Peter Korsgaard
  0 siblings, 1 reply; 7+ messages in thread
From: Fiona Klute via buildroot @ 2026-02-27 19:21 UTC (permalink / raw)
  To: buildroot
  Cc: Ricardo Martincoski, Jimmy Durand Wesolowski, Julien Olivain,
	guenther.harrasser, Fiona Klute

With Python 3.14 the default process start method in the
multiprocessing module for POSIX platfroms changed from "fork" to
"forkserver". Unlike with "fork" the new process does not inherit
loaded modules, classes, etc., instead it has to load any it
needs. This means that class variables modified in the parent process
are lost, which breaks the way support/testing/run-tests sets
configuration in BRConfigTest.

Instead add a method to serialize the configuration into an
environment variable, and read it during
BRConfigTest.__init__(). Reading is skipped if the environment
variable is not set so test discovery (not execution) works without
configuration (e.g. utils/get-developers uses this).

The (de-)serialization could be simpler using a dedicated
@dataclasses.dataclass class, but the dataclasses module was added
with Python 3.7, while support/dependencies/check-host-python3.mk
specifies 3.4 as the minimum for Buildroot.

Remove the "fork" method override added in
3d2141bceefda32bef06ddda594eaf8665913276. This fixes a crash that
occured in combination with an incorrect [1] patch added to the Debian
python3-nose2 package with version 0.15.1-2 [2] because setting the
default multiprocessing start method twice is an error.

[1] https://github.com/nose-devs/nose2/pull/644#issuecomment-3902982437
[2] https://salsa.debian.org/python-team/packages/nose2/-/blob/debian/0.15.1-2/debian/patches/0004-plugins-mp-set-context-to-fork-for-Python-3.14-mp-AP.patch?ref_type=tags

Signed-off-by: Fiona Klute <fiona.klute@gmx.de>
---
I'd be happy to rewrite using @dataclasses.dataclass if a bit less
backwards compatibility is fine, but getting that crash fixed is more
important to me. That said, the oldest Python version still supported
upstream is 3.10, Debian Trixie has 3.13, Bookworm (oldstable) 3.11,
so maybe raising the requirement a little is fine?

 support/testing/infra/basetest.py | 33 +++++++++++++++++++++++++++++++
 support/testing/run-tests         |  3 ++-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/support/testing/infra/basetest.py b/support/testing/infra/basetest.py
index 13f9b2d398..55567448fe 100644
--- a/support/testing/infra/basetest.py
+++ b/support/testing/infra/basetest.py
@@ -1,6 +1,7 @@
 import unittest
 import os
 import datetime
+import json
 
 from infra.builder import Builder
 from infra.emulator import Emulator
@@ -33,8 +34,16 @@ class BRConfigTest(unittest.TestCase):
     jlevel = 0
     timeout_multiplier = 1
 
+    # name of the environment variable for config transfer
+    CONF_ENV = 'BR_TEST_CONFIG_JSON'
+    _CONF_FIELDS = (
+        'downloaddir', 'outputdir', 'logtofile', 'keepbuilds', 'jlevel',
+        'timeout_multiplier')
+
     def __init__(self, names):
         super(BRConfigTest, self).__init__(names)
+        if self.CONF_ENV in os.environ:
+            self.load_conf(os.environ[self.CONF_ENV])
         self.testname = self.__class__.__name__
         self.builddir = self.outputdir and os.path.join(self.outputdir, self.testname)
         self.config += '\nBR2_DL_DIR="{}"\n'.format(self.downloaddir)
@@ -44,6 +53,30 @@ class BRConfigTest(unittest.TestCase):
         print("{} {:40s} {}".format(datetime.datetime.now().strftime("%H:%M:%S"),
                                     self.testname, msg))
 
+    @classmethod
+    def dump_conf(cls) -> str:
+        """support/testing/run-tests builds runtime config in class
+        variables, and then uses this method to serialize them into an
+        environment variable. On instantiation, tests use load_conf()
+        (below) to load this configuration. That way configuration can
+        be transferred into multiprocessing worker processes without
+        requiring the "fork" start method.
+
+        """
+        conf = dict()
+        for c in cls._CONF_FIELDS:
+            v = getattr(cls, c)
+            assert v is not None
+            conf[c] = v
+        return json.dumps(conf)
+
+    def load_conf(self, data: str) -> None:
+        conf = json.loads(data)
+        for c in self._CONF_FIELDS:
+            v = conf[c]
+            assert v is not None
+            setattr(self, c, v)
+
     def setUp(self):
         self.show_msg("Starting")
         self.b = Builder(self.config, self.builddir, self.logtofile, self.jlevel)
diff --git a/support/testing/run-tests b/support/testing/run-tests
index 1c4d2b4a85..8a79cbb104 100755
--- a/support/testing/run-tests
+++ b/support/testing/run-tests
@@ -127,6 +127,8 @@ def main():
         return 1
     BRConfigTest.timeout_multiplier = args.timeout_multiplier
 
+    os.environ[BRConfigTest.CONF_ENV] = BRConfigTest.dump_conf()
+
     nose2_args = ["-v",
                   "-N", str(args.testcases),
                   "-s", test_dir,
@@ -142,5 +144,4 @@ def main():
 
 
 if __name__ == "__main__":
-    multiprocessing.set_start_method("fork")
     sys.exit(main())
-- 
2.51.0

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