It is not type safe, but it's the best that can be done without
const_refs_static.  It can also be used with BqlCell and BqlRefCell.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/qemu-api/src/vmstate.rs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/rust/qemu-api/src/vmstate.rs b/rust/qemu-api/src/vmstate.rs
index 8f32c72a0fd..94a2a29fe7e 100644
--- a/rust/qemu-api/src/vmstate.rs
+++ b/rust/qemu-api/src/vmstate.rs
@@ -628,6 +628,39 @@ 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 $vmsd
+// which is what really would matter.
+#[doc(alias = "VMSTATE_STRUCT")]
+#[macro_export]
+macro_rules! vmstate_struct {
+    ($struct_name:ty, $field_name:ident $([0 .. $num:ident $(* $factor:expr)?])?, $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,
+            $(.num_offset: $crate::offset_of!($struct_name, $num),)?
+            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 $(
+                .with_varray_flag($crate::call_func_with_field!(
+                    $crate::vmstate::vmstate_varray_flag,
+                    $struct_name,
+                    $num))
+               $(.with_varray_multiply($factor))?)?
+        }
+    };
+}
+
 #[doc(alias = "VMSTATE_CLOCK_V")]
 #[macro_export]
 macro_rules! vmstate_clock_v {
-- 
2.47.1

On Fri, Jan 17, 2025 at 10:00:43AM +0100, Paolo Bonzini wrote:
> Date: Fri, 17 Jan 2025 10:00:43 +0100
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [PATCH 07/10] rust: qemu_api: add vmstate_struct
> X-Mailer: git-send-email 2.47.1
> 
> It is not type safe, but it's the best that can be done without
> const_refs_static.  It can also be used with BqlCell and BqlRefCell.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  rust/qemu-api/src/vmstate.rs | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)

...

> +#[doc(alias = "VMSTATE_STRUCT")]
> +#[macro_export]
> +macro_rules! vmstate_struct {
> +    ($struct_name:ty, $field_name:ident $([0 .. $num:ident $(* $factor:expr)?])?, $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,
> +            $(.num_offset: $crate::offset_of!($struct_name, $num),)?
> +            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 },

Yes, this `unsafe` is fitting.

> +            ..$crate::zeroable::Zeroable::ZERO $(
> +                .with_varray_flag($crate::call_func_with_field!(
> +                    $crate::vmstate::vmstate_varray_flag,
> +                    $struct_name,
> +                    $num))
> +               $(.with_varray_multiply($factor))?)?
> +        }
> +    };
> +}
> +

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