[17/39] tests/functional: add a QMP backdoor for debugging stalled tests

Commit Message

Alex Bennée Nov. 21, 2024, 4:57 p.m. UTC

From: Daniel P. Berrangé <[e-mail]>

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 <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Alex Bennée <[e-mail]>
---
 docs/devel/testing/functional.rst      | 10 ++++++++++
 tests/functional/qemu_test/testcase.py |  7 +++++++
 2 files changed, 17 insertions(+)

Comments

Thomas Huth Nov. 21, 2024, 7:41 p.m. UTC | #1

On 21/11/2024 17.57, Alex Bennée wrote:
> From: Daniel P. Berrangé <[e-mail]>
> 
> 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 <[e-mail]>
> Message-Id: <[e-mail]>
> Signed-off-by: Alex Bennée <[e-mail]>
> ---
>   docs/devel/testing/functional.rst      | 10 ++++++++++
>   tests/functional/qemu_test/testcase.py |  7 +++++++
>   2 files changed, 17 insertions(+)
> 
> 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

Reviewed-by: Thomas Huth <[e-mail]>

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