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[PULL,17/28] tests/functional: add a QMP backdoor for debugging stalled tests

Message ID 20241125152105.2100395-18-alex.bennee@linaro.org
State New
Headers show
Series [PULL,01/28] tests/functional: fix mips64el test to honour workdir | expand

Commit Message

Alex Bennée Nov. 25, 2024, 3:20 p.m. UTC 
From: Daniel P. Berrangé <berrange@redhat.com>

Support the QEMU_TEST_QMP_BACKDOOR=backdoor.sock env variable as a
way to get a QMP backdoor for debugging a stalled QEMU test. Most
typically this would be used if running the tests directly:

 $ QEMU_TEST_QMP_BACKDOOR=backdoor.sock \
   QEMU_TEST_QEMU_BINARY=./build/qemu-system-arm \
   PYTHONPATH=./python \
   ./tests/functional/test_arm_tuxrun.py

And then, when the test stalls, in a second shell run:

 $ ./scripts/qmp/qmp-shell backdoor.sock

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20241121154218.1423005-18-berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20241121165806.476008-18-alex.bennee@linaro.org>
diff mbox series

Patch

diff --git a/docs/devel/testing/functional.rst b/docs/devel/testing/functional.rst
index 6b5d0c5b98..b8ad7b0bf7 100644
--- a/docs/devel/testing/functional.rst
+++ b/docs/devel/testing/functional.rst
@@ -176,6 +176,16 @@  primarily depend on the value of the ``qemu_bin`` class attribute.
 If it is not explicitly set by the test code, its default value will
 be the result the QEMU_TEST_QEMU_BINARY environment variable.
 
+Debugging hung QEMU
+^^^^^^^^^^^^^^^^^^^
+
+When test cases go wrong it may be helpful to debug a stalled QEMU
+process. While the QEMUMachine class owns the primary QMP monitor
+socket, it is possible to request a second QMP monitor be created
+by setting the ``QEMU_TEST_QMP_BACKDOOR`` env variable to refer
+to a UNIX socket name. The ``qmp-shell`` command can then be
+attached to the stalled QEMU to examine its live state.
+
 Attribute reference
 -------------------
 
diff --git a/tests/functional/qemu_test/testcase.py b/tests/functional/qemu_test/testcase.py
index e2a329c3e5..fceafb32b0 100644
--- a/tests/functional/qemu_test/testcase.py
+++ b/tests/functional/qemu_test/testcase.py
@@ -175,6 +175,13 @@  def _new_vm(self, name, *args):
                          log_dir=self.logdir)
         self.log.debug('QEMUMachine "%s" created', name)
         self.log.debug('QEMUMachine "%s" temp_dir: %s', name, vm.temp_dir)
+
+        sockpath = os.environ.get("QEMU_TEST_QMP_BACKDOOR", None)
+        if sockpath is not None:
+            vm.add_args("-chardev",
+                        f"socket,id=backdoor,path={sockpath},server=on,wait=off",
+                        "-mon", "chardev=backdoor,mode=control")
+
         if args:
             vm.add_args(*args)
         return vm