Re: [PATCH 18/26] rust: qom: add possibility of overriding unparent

[Zhao Liu <zhao1.liu@intel.com>]

On Mon, Dec 09, 2024 at 01:37:09PM +0100, Paolo Bonzini wrote:
> Date: Mon,  9 Dec 2024 13:37:09 +0100
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [PATCH 18/26] rust: qom: add possibility of overriding unparent
> X-Mailer: git-send-email 2.47.1
> 
> Add a blanket definition of ClassInitImpl<ObjectClass> that thunks
> ObjectImpl::UNPARENT and overrides it in ObjectClass if it is not
> None.
>
> ClassInitImpl<DeviceClass> can now call its superclass's ClassInitImpl,
> so that the C and Rust hierarchies match more closely.
> 
> This is mostly done as an example of implementing the metaclass
> hierarchy under ClassInitImpl.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  rust/qemu-api/src/definitions.rs  | 44 ++++++++++++++++++++++++++++---
>  rust/qemu-api/src/device_class.rs |  6 +++--
>  2 files changed, 45 insertions(+), 5 deletions(-)

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>

(with an additional comment below...)

> diff --git a/rust/qemu-api/src/definitions.rs b/rust/qemu-api/src/definitions.rs
> index 2429b9f53f0..958ea34decc 100644
> --- a/rust/qemu-api/src/definitions.rs
> +++ b/rust/qemu-api/src/definitions.rs
> @@ -6,7 +6,7 @@
>  
>  use std::{ffi::CStr, os::raw::c_void};
>  
> -use crate::bindings::{Object, ObjectClass, TypeInfo};
> +use crate::bindings::{self, Object, ObjectClass, TypeInfo};
>  
>  unsafe extern "C" fn rust_instance_init<T: ObjectImpl>(obj: *mut Object) {
>      // SAFETY: obj is an instance of T, since rust_instance_init<T>
> @@ -115,6 +115,9 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
>          class_data: core::ptr::null_mut(),
>          interfaces: core::ptr::null_mut(),
>      };
> +
> +    // methods on ObjectClass
> +    const UNPARENT: Option<fn(&mut Self)> = None;
>  }

Will we change `&mut Self` to an immutable reference in the future?

IIUC, the parent on the C side also has a pointer to current object.