include/qom/object.h: New OBJECT_DEFINE_SIMPLE_TYPE{, _WITH_INTERFACES} macros

We have an OBJECT_DEFINE_TYPE_EXTENDED macro, plus several variations
on it, which emits the boilerplate for the TypeInfo and ensures it is
registered with the type system.  However, all the existing macros
insist that the type being defined has its own FooClass struct, so
they aren't useful for the common case of a simple leaf class which
doesn't have any new methods or any other need for its own class
struct (that is, for the kind of type that OBJECT_DECLARE_SIMPLE_TYPE
declares).

Pull the actual implementation of OBJECT_DEFINE_TYPE_EXTENDED out
into a new DO_OBJECT_DEFINE_TYPE_EXTENDED which parameterizes the
value we use for the class_size field.  This lets us add a new
OBJECT_DEFINE_SIMPLE_TYPE which does the same job as the various
existing OBJECT_DEFINE_*_TYPE_* family macros for this kind of simple
type, and the variant OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES for
when the type will implement some interfaces.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240220160622.114437-5-peter.maydell@linaro.org
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>

1 files changed, 29 insertions, 5 deletions

diff --git a/docs/devel/qom.rst b/docs/devel/qom.rst
index 9918fac..0889ca9 100644
--- a/docs/devel/qom.rst
+++ b/docs/devel/qom.rst
@@ -348,12 +348,14 @@ used. This does the same as OBJECT_DECLARE_SIMPLE_TYPE(), but without
 the 'struct MyDeviceClass' definition.
 
 To implement the type, the OBJECT_DEFINE macro family is available.
-In the simple case the OBJECT_DEFINE_TYPE macro is suitable:
+For the simplest case of a leaf class which doesn't need any of its
+own virtual functions (i.e. which was declared with OBJECT_DECLARE_SIMPLE_TYPE)
+the OBJECT_DEFINE_SIMPLE_TYPE macro is suitable:
 
 .. code-block:: c
    :caption: Defining a simple type
 
-   OBJECT_DEFINE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)
+   OBJECT_DEFINE_SIMPLE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)
 
 This is equivalent to the following:
 
@@ -370,7 +372,6 @@ This is equivalent to the following:
        .instance_size = sizeof(MyDevice),
        .instance_init = my_device_init,
        .instance_finalize = my_device_finalize,
-       .class_size = sizeof(MyDeviceClass),
        .class_init = my_device_class_init,
    };
 
@@ -385,13 +386,36 @@ This is sufficient to get the type registered with the type
 system, and the three standard methods now need to be implemented
 along with any other logic required for the type.
 
+If the class needs its own virtual methods, or has some other
+per-class state it needs to store in its own class struct,
+then you can use the OBJECT_DEFINE_TYPE macro. This does the
+same thing as OBJECT_DEFINE_SIMPLE_TYPE, but it also sets the
+class_size of the type to the size of the class struct.
+
+.. code-block:: c
+   :caption: Defining a type which needs a class struct
+
+   OBJECT_DEFINE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)
+
 If the type needs to implement one or more interfaces, then the
-OBJECT_DEFINE_TYPE_WITH_INTERFACES() macro can be used instead.
-This accepts an array of interface type names.
+OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES() and
+OBJECT_DEFINE_TYPE_WITH_INTERFACES() macros can be used instead.
+These accept an array of interface type names. The difference between
+them is that the former is for simple leaf classes that don't need
+a class struct, and the latter is for when you will be defining
+a class struct.
 
 .. code-block:: c
    :caption: Defining a simple type implementing interfaces
 
+   OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(MyDevice, my_device,
+                                             MY_DEVICE, DEVICE,
+                                             { TYPE_USER_CREATABLE },
+                                             { NULL })
+
+.. code-block:: c
+   :caption: Defining a type implementing interfaces
+
    OBJECT_DEFINE_TYPE_WITH_INTERFACES(MyDevice, my_device,
                                       MY_DEVICE, DEVICE,
                                       { TYPE_USER_CREATABLE },