Re: [RFC PATCH 7/9] rust: qemu_api: add vmstate_struct and vmstate_cell

[Paolo Bonzini <pbonzini@redhat.com>]

On Tue, Dec 31, 2024 at 1:23 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> These are not type safe, but they're the best that can be done without
> const_refs_static.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

FWIW, I'll change these patch to support varrays in v2.

Paolo

> ---
>  rust/qemu-api/src/vmstate.rs | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/rust/qemu-api/src/vmstate.rs b/rust/qemu-api/src/vmstate.rs
> index b59a4b66339..e45c93587b2 100644
> --- a/rust/qemu-api/src/vmstate.rs
> +++ b/rust/qemu-api/src/vmstate.rs
> @@ -610,6 +610,40 @@ macro_rules! vmstate_array_of_pointer_to_struct {
>      }};
>  }
>
> +// FIXME: including the `vmsd` field in a `const` is not possible without
> +// the const_refs_static feature (stabilized in Rust 1.83.0).  Without it,
> +// it is not possible to use VMS_STRUCT in a transparent manner using
> +// `vmstate_of!`.  While VMSTATE_CLOCK can at least try to be type-safe,
> +// VMSTATE_STRUCT includes $type only for documentation purposes; it
> +// is checked against $field_name and $struct_name, but not against $vmsd
> +// which is what really would matter.
> +#[doc(alias = "VMSTATE_STRUCT")]
> +#[macro_export]
> +macro_rules! vmstate_struct {
> +    ($field_name:ident, $struct_name:ty, $vmsd:expr, $type:ty) => {{
> +        $crate::bindings::VMStateField {
> +            name: ::core::concat!(::core::stringify!($field_name), "\0")
> +                .as_bytes()
> +                .as_ptr() as *const ::std::os::raw::c_char,
> +            offset: {
> +                $crate::assert_field_type!($struct_name, $field_name, $type);
> +                $crate::offset_of!($struct_name, $field_name)
> +            }
> +            size: ::core::mem::size_of::<$type>(),
> +            flags: $crate::bindings::VMStateFlags::VMS_STRUCT,
> +            vmsd: unsafe { $vmsd },
> +            ..$crate::zeroable::Zeroable::ZERO
> +        }
> +    }};
> +}
> +
> +#[macro_export]
> +macro_rules! vmstate_cell {
> +    ($field_name:ident, $struct_name:ty, $vmsd:expr, $type:ty) => {
> +        $crate::vmstate_struct!($field_name, $struct_name, $vmsd, $type)
> +    };
> +}
> +
>  #[doc(alias = "VMSTATE_CLOCK_V")]
>  #[macro_export]
>  macro_rules! vmstate_clock_v {
> --
> 2.47.1
>