qemudriver: add a qemu-default display option

The barebox test suite adds an --interactive option to pytest, which
allows starting QEMU interactively with the Labgrid Environment YAML to
allow manual testing.

So far, it wasn't possible to use this with an interactive graphic output,
because Labgrid allowed only headless displays or none.

none is the default and will configure QEMU with -nographic, which
can not be overridden later on and -display also has no default value.

To support this use case, add a qemu-default option, which instructs
Labgrid to now touch -nographic and -display at all.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Author: a3f

CHANGES.rst

@@ -17,6 +17,9 @@ more performant and the import times are shorter.
 New Features in 24.1
 ~~~~~~~~~~~~~~~~~~~~
 - All components can be installed into the same virtualenv again.
+- The `QEMUDriver` now supports setting the ``display`` option to
+  ``qemu-default``, which will neither set the QEMU ``-display`` option
+  or pass along ``-nographic``.
 
 Bug fixes in 24.1
 ~~~~~~~~~~~~~~~~~

doc/configuration.rst

@@ -2726,6 +2726,7 @@ Arguments:
     - none: Do not create a display device
     - fb-headless: Create a headless framebuffer device
     - egl-headless: Create a headless GPU-backed graphics card. Requires host support
+    - qemu-default: Don't override QEMU default settings
 
   - nic (str): optional, configuration string to pass to QEMU to create a network interface
 

labgrid/driver/qemudriver.py

@@ -48,6 +48,7 @@ class QEMUDriver(ConsoleExpectMixin, Driver, PowerProtocol, ConsoleProtocol):
             none: Do not create a display device
             fb-headless: Create a headless framebuffer device
             egl-headless: Create a headless GPU-backed graphics card. Requires host support
+            qemu-default: Don't override QEMU default settings
         nic (str): optional, configuration string to pass to QEMU to create a network interface
     """
     qemu_bin = attr.ib(validator=attr.validators.instance_of(str))
@@ -85,7 +86,9 @@ class QEMUDriver(ConsoleExpectMixin, Driver, PowerProtocol, ConsoleProtocol):
         default="none",
         validator=attr.validators.optional(attr.validators.and_(
             attr.validators.instance_of(str),
-            attr.validators.in_(["none", "fb-headless", "egl-headless"]),
+            attr.validators.in_(
+                ["none", "fb-headless", "egl-headless", "qemu-default"]
+            ),
         ))
     )
     nic = attr.ib(
@@ -211,7 +214,7 @@ def get_qemu_base_args(self):
                 cmd.append("virtio")
             cmd.append("-display")
             cmd.append("egl-headless")
-        else:
+        elif self.display != "qemu-default":
             raise ExecutionError(f"Unknown display '{self.display}'")
 
         if self.nic: