python/qemu: dump a developer friendly version of cmdline to logs

Now we have the arguments nicely split up we can make _console_args a
function call and present a slightly different version to the logs to
save developers manually hacking the command line up.

Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20260619155657.944220-4-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

python/qemu/machine/machine.py

@@ -308,12 +308,15 @@ class QEMUMachine:
                          'chardev=mon,mode=control'])
         return args
 
-    @property
-    def _console_args(self) -> List[str]:
+    def _console_args(self, interactive: bool = False) -> List[str]:
         args: List[str] = []
+        # redirect pre_console_index serials to null
         for _ in range(self._console_index):
             args.extend(['-serial', 'null'])
-        if self._console_set:
+
+        if interactive:
+            args.extend(['-serial', 'mon:stdio'])
+        elif self._console_set:
             assert self._cons_sock_pair is not None
             fd = self._cons_sock_pair[0].fileno()
             chardev = f"socket,id=console,fd={fd}"
@@ -376,7 +379,7 @@ class QEMUMachine:
             self._wrapper,
             [self._binary],
             self._harness_args,
-            self._console_args,
+            self._console_args(),
             self._base_args,
             self._args
         ))
@@ -485,6 +488,14 @@ class QEMUMachine:
         """
         self._pre_launch()
         LOG.debug('VM launch command: %r', ' '.join(self._qemu_full_args))
+        # Log a simplified, developer-runnable command:
+        # Exclude harness-managed infrastructure args (harness_args)
+        # and wrapper.
+        debug_cmd = [self._binary]
+        debug_cmd.extend(self._console_args(interactive=True))
+        debug_cmd.extend(self._base_args)
+        debug_cmd.extend(self._args)
+        LOG.debug('Developer-runnable command: %r', ' '.join(debug_cmd))
 
         # Cleaning up of this subprocess is guaranteed by _do_shutdown.
         # pylint: disable=consider-using-with