On Mon, May 5, 2025 at 12:04 PM Paolo Bonzini <pbonz...@redhat.com> wrote:
>
> The proposed suggestion is not correct. First it is not necessary for
> *all* classes to be Zeroable, only for Rust-defined ones; classes
> defined in C never implement ObjectImpl.
>
> Second, the parent class field need not be Zeroable. For example,
> ChardevClass's chr_write and chr_be_event fields cannot be NULL,
> therefore ChardevClass cannot be Zeroable. However, char_class_init()
> initializes them, therefore ChardevClass could be subclassed by Rust code.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> rust/qemu-api/src/qom.rs | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs
> index 6929e4d33ae..52e3a1ec981 100644
> --- a/rust/qemu-api/src/qom.rs
> +++ b/rust/qemu-api/src/qom.rs
> @@ -534,9 +534,10 @@ pub trait ObjectImpl: ObjectType + IsA<Object> {
> /// While `klass`'s parent class is initialized on entry, the other
> fields
> /// are all zero; it is therefore assumed that all fields in `T` can be
> /// zeroed, otherwise it would not be possible to provide the class as a
> - /// `&mut T`. TODO: add a bound of
> [`Zeroable`](crate::zeroable::Zeroable)
> - /// to T; this is more easily done once Zeroable does not require a
> manual
> - /// implementation (Rust 1.75.0).
> + /// `&mut T`. TODO: it may be possible to add an unsafe trait that
> checks
> + /// that all fields *after the parent class* (but not the parent class
> + /// itself) are Zeroable. This unsafe trait can be added via a derive
> + /// macro.
> const CLASS_INIT: fn(&mut Self::Class);
> }
>
> --
> 2.49.0
>
Reviewed-by: Manos Pitsidianakis <manos.pitsidiana...@linaro.org>
