[PULL 03/11] qdev: Implement qdev_create_fake_machine() for user emulation

[Philippe Mathieu-Daudé]

When a QDev instance is realized, qdev_get_machine() ends up called.
In the next commit, qdev_get_machine() will require a "machine"
container to be always present. To satisfy this QOM containers design,
Implement qdev_create_fake_machine() which creates a fake "machine"
container for user emulation.

On system emulation, qemu_create_machine() is called from qemu_init().
For user emulation, since the TCG accelerator always calls
tcg_init_machine(), we use it to hook our fake machine creation.

Suggested-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250102211800.79235-2-philmd@linaro.org>
---
 include/hw/qdev-core.h | 10 ++++++++++
 accel/tcg/tcg-all.c    |  8 +++++++-
 hw/core/qdev-user.c    | 19 +++++++++++++++++++
 hw/core/meson.build    |  1 +
 4 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 hw/core/qdev-user.c

diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index c4d3dc39064..50cbbf81211 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -1023,6 +1023,16 @@ const char *qdev_fw_name(DeviceState *dev);
 void qdev_assert_realized_properly(void);
 Object *qdev_get_machine(void);
 
+/**
+ * qdev_create_fake_machine(): Create a fake machine container.
+ *
+ * .. note::
+ *    This function is a kludge for user emulation (USER_ONLY)
+ *    because when thread (TYPE_CPU) are realized, qdev_realize()
+ *    access a machine container.
+ */
+void qdev_create_fake_machine(void);
+
 /**
  * qdev_get_human_name() - Return a human-readable name for a device
  * @dev: The device. Must be a valid and non-NULL pointer.
diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index c2565758876..95adaacee82 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -35,7 +35,9 @@
 #include "qemu/atomic.h"
 #include "qapi/qapi-builtin-visit.h"
 #include "qemu/units.h"
-#if !defined(CONFIG_USER_ONLY)
+#if defined(CONFIG_USER_ONLY)
+#include "hw/qdev-core.h"
+#else
 #include "hw/boards.h"
 #endif
 #include "internal-common.h"
@@ -124,6 +126,10 @@ static int tcg_init_machine(MachineState *ms)
     tcg_prologue_init();
 #endif
 
+#ifdef CONFIG_USER_ONLY
+    qdev_create_fake_machine();
+#endif
+
     return 0;
 }
 
diff --git a/hw/core/qdev-user.c b/hw/core/qdev-user.c
new file mode 100644
index 00000000000..3d421d8f4e5
--- /dev/null
+++ b/hw/core/qdev-user.c
@@ -0,0 +1,19 @@
+/*
+ * QDev helpers specific to user emulation.
+ *
+ * Copyright 2025 Linaro, Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include "qemu/osdep.h"
+#include "qom/object.h"
+#include "hw/qdev-core.h"
+
+void qdev_create_fake_machine(void)
+{
+    Object *fake_machine_obj;
+
+    fake_machine_obj = object_property_add_new_container(object_get_root(),
+                                                         "machine");
+    object_property_add_new_container(fake_machine_obj, "unattached");
+}
diff --git a/hw/core/meson.build b/hw/core/meson.build
index ce9dfa3f4bf..65a1698ed1f 100644
--- a/hw/core/meson.build
+++ b/hw/core/meson.build
@@ -46,3 +46,4 @@ system_ss.add(files(
   'vm-change-state-handler.c',
   'clock-vmstate.c',
 ))
+user_ss.add(files('qdev-user.c'))
-- 
2.47.1