[PATCH 0/2] qom: Introduce class_post_init() handler

[PATCH 0/2] qom: Introduce class_post_init() handler

[Philippe Mathieu-Daudé]

Add a class_post_init() handler to be called by parents
*after* child class_init() handler is called. This is
necessary to have parent class check children properly
set some values or mandatory handlers.

Philippe Mathieu-Daudé (2):
  qom: Declare class_base_init() before class_init()
  qom: Introduce class_post_init() handler

 include/qom/object.h     | 17 ++++++++++-------
 qom/object.c             | 14 ++++++++++++--
 rust/qemu-api/src/qom.rs |  8 +++++++-
 3 files changed, 29 insertions(+), 10 deletions(-)

-- 
2.47.1

[PATCH 1/2] qom: Declare class_base_init() before class_init()

[Philippe Mathieu-Daudé]

Since class_base_init() is called *before* class_init(),
move its declaration in TypeInfo before class_init() to
help a bit. No logical change.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 include/qom/object.h     | 10 +++++-----
 qom/object.c             |  4 ++--
 rust/qemu-api/src/qom.rs |  2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/qom/object.h b/include/qom/object.h
index 9192265db76..3776267e903 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -457,14 +457,14 @@ struct Object
  *   assumed to be the size of the parent class.  This allows a type to avoid
  *   implementing an explicit class type if they are not adding additional
  *   virtual functions.
- * @class_init: This function is called after all parent class initialization
- *   has occurred to allow a class to set its default virtual method pointers.
- *   This is also the function to use to override virtual methods from a parent
- *   class.
  * @class_base_init: This function is called for all base classes after all
  *   parent class initialization has occurred, but before the class itself
  *   is initialized.  This is the function to use to undo the effects of
  *   memcpy from the parent class to the descendants.
+ * @class_init: This function is called after all parent class initialization
+ *   has occurred to allow a class to set its default virtual method pointers.
+ *   This is also the function to use to override virtual methods from a parent
+ *   class.
  * @class_data: Data to pass to the @class_init,
  *   @class_base_init. This can be useful when building dynamic
  *   classes.
@@ -486,8 +486,8 @@ struct TypeInfo
     bool abstract;
     size_t class_size;
 
-    void (*class_init)(ObjectClass *klass, void *data);
     void (*class_base_init)(ObjectClass *klass, void *data);
+    void (*class_init)(ObjectClass *klass, void *data);
     void *class_data;
 
     InterfaceInfo *interfaces;
diff --git a/qom/object.c b/qom/object.c
index ec447f14a78..1a686dff5a0 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -54,8 +54,8 @@ struct TypeImpl
     size_t instance_size;
     size_t instance_align;
 
-    void (*class_init)(ObjectClass *klass, void *data);
     void (*class_base_init)(ObjectClass *klass, void *data);
+    void (*class_init)(ObjectClass *klass, void *data);
 
     void *class_data;
 
@@ -119,8 +119,8 @@ static TypeImpl *type_new(const TypeInfo *info)
     ti->instance_size = info->instance_size;
     ti->instance_align = info->instance_align;
 
-    ti->class_init = info->class_init;
     ti->class_base_init = info->class_base_init;
+    ti->class_init = info->class_init;
     ti->class_data = info->class_data;
 
     ti->instance_init = info->instance_init;
diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs
index 97901fb9084..6033228e338 100644
--- a/rust/qemu-api/src/qom.rs
+++ b/rust/qemu-api/src/qom.rs
@@ -486,8 +486,8 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
         instance_finalize: Some(drop_object::<Self>),
         abstract_: Self::ABSTRACT,
         class_size: core::mem::size_of::<Self::Class>(),
-        class_init: Some(rust_class_init::<Self>),
         class_base_init: Self::CLASS_BASE_INIT,
+        class_init: Some(rust_class_init::<Self>),
         class_data: core::ptr::null_mut(),
         interfaces: core::ptr::null_mut(),
     };
-- 
2.47.1

[PATCH 2/2] qom: Introduce class_post_init() handler

[Philippe Mathieu-Daudé]

Add a class_post_init() handler to be called by parents
*after* child class_init() handler is called. This is
necessary to have parent class check children properly
set some values or mandatory handlers.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 include/qom/object.h     |  7 +++++--
 qom/object.c             | 10 ++++++++++
 rust/qemu-api/src/qom.rs |  6 ++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/qom/object.h b/include/qom/object.h
index 3776267e903..d1e437a81be 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -465,8 +465,10 @@ struct Object
  *   has occurred to allow a class to set its default virtual method pointers.
  *   This is also the function to use to override virtual methods from a parent
  *   class.
- * @class_data: Data to pass to the @class_init,
- *   @class_base_init. This can be useful when building dynamic
+ * @class_post_init: This function is called to finish initialization of
+ *   a class, after all @class_init functions were called.
+ * @class_data: Data to pass to the @class_base_init, @class_init, and
+ *   @class_post_init. This can be useful when building dynamic
  *   classes.
  * @interfaces: The list of interfaces associated with this type.  This
  *   should point to a static array that's terminated with a zero filled
@@ -488,6 +490,7 @@ struct TypeInfo
 
     void (*class_base_init)(ObjectClass *klass, void *data);
     void (*class_init)(ObjectClass *klass, void *data);
+    void (*class_post_init)(ObjectClass *klass, void *data);
     void *class_data;
 
     InterfaceInfo *interfaces;
diff --git a/qom/object.c b/qom/object.c
index 1a686dff5a0..694009f0c94 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -56,6 +56,7 @@ struct TypeImpl
 
     void (*class_base_init)(ObjectClass *klass, void *data);
     void (*class_init)(ObjectClass *klass, void *data);
+    void (*class_post_init)(ObjectClass *klass, void *data);
 
     void *class_data;
 
@@ -121,6 +122,7 @@ static TypeImpl *type_new(const TypeInfo *info)
 
     ti->class_base_init = info->class_base_init;
     ti->class_init = info->class_init;
+    ti->class_post_init = info->class_post_init;
     ti->class_data = info->class_data;
 
     ti->instance_init = info->instance_init;
@@ -416,6 +418,14 @@ static void type_initialize(TypeImpl *ti)
     if (ti->class_init) {
         ti->class_init(ti->class, ti->class_data);
     }
+
+    parent = type_get_parent(ti);
+    while (parent) {
+        if (parent->class_post_init) {
+            parent->class_post_init(ti->class, ti->class_data);
+        }
+        parent = type_get_parent(parent);
+    }
 }
 
 static void object_init_with_type(Object *obj, TypeImpl *ti)
diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs
index 6033228e338..d95e90153a9 100644
--- a/rust/qemu-api/src/qom.rs
+++ b/rust/qemu-api/src/qom.rs
@@ -470,6 +470,11 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
         unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void),
     > = None;
 
+    /// Called to finish initialization of a class.
+    const CLASS_POST_INIT: Option<
+        unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void),
+    > = None;
+
     const TYPE_INFO: TypeInfo = TypeInfo {
         name: Self::TYPE_NAME.as_ptr(),
         parent: Self::ParentType::TYPE_NAME.as_ptr(),
@@ -488,6 +493,7 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
         class_size: core::mem::size_of::<Self::Class>(),
         class_base_init: Self::CLASS_BASE_INIT,
         class_init: Some(rust_class_init::<Self>),
+        class_post_init: Self::CLASS_POST_INIT,
         class_data: core::ptr::null_mut(),
         interfaces: core::ptr::null_mut(),
     };
-- 
2.47.1

Re: [PATCH 2/2] qom: Introduce class_post_init() handler

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> Add a class_post_init() handler to be called by parents
> *after* child class_init() handler is called. This is
> necessary to have parent class check children properly
> set some values or mandatory handlers.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Plausible, but I'd like to see actual use.  What uses do you have in
mind?

Re: [PATCH 2/2] qom: Introduce class_post_init() handler

[Philippe Mathieu-Daudé]

On 27/1/25 08:00, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <philmd@linaro.org> writes:
> 
>> Add a class_post_init() handler to be called by parents
>> *after* child class_init() handler is called. This is
>> necessary to have parent class check children properly
>> set some values or mandatory handlers.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> 
> Plausible, but I'd like to see actual use.  What uses do you have in
> mind?

See for example:
https://lore.kernel.org/qemu-devel/20250125170125.32855-25-philmd@linaro.org/

Where the abstract parent CPUClass checks concrete target implementation
registered a handler.

(I'll cc you on another use shortly).

Re: [PATCH 0/2] qom: Introduce class_post_init() handler

[Richard Henderson]

On 1/25/25 08:58, Philippe Mathieu-Daudé wrote:
> Add a class_post_init() handler to be called by parents
> *after* child class_init() handler is called. This is
> necessary to have parent class check children properly
> set some values or mandatory handlers.
> 
> Philippe Mathieu-Daudé (2):
>    qom: Declare class_base_init() before class_init()
>    qom: Introduce class_post_init() handler
> 
>   include/qom/object.h     | 17 ++++++++++-------
>   qom/object.c             | 14 ++++++++++++--
>   rust/qemu-api/src/qom.rs |  8 +++++++-
>   3 files changed, 29 insertions(+), 10 deletions(-)
> 

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~

Re: [PATCH 0/2] qom: Introduce class_post_init() handler

[Paolo Bonzini]

On 1/25/25 17:58, Philippe Mathieu-Daudé wrote:
> Add a class_post_init() handler to be called by parents
> *after* child class_init() handler is called. This is
> necessary to have parent class check children properly
> set some values or mandatory handlers.
> 
> Philippe Mathieu-Daudé (2):
>    qom: Declare class_base_init() before class_init()
>    qom: Introduce class_post_init() handler
> 
>   include/qom/object.h     | 17 ++++++++++-------
>   qom/object.c             | 14 ++++++++++++--
>   rust/qemu-api/src/qom.rs |  8 +++++++-
>   3 files changed, 29 insertions(+), 10 deletions(-)

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo