rust: qdev: const_refs_to_static

Now that const_refs_static can be assumed, convert the members of
the DeviceImpl trait from functions to constants.  This lets the
compiler know that they have a 'static lifetime, and removes the
need for the weird "Box::leak()".

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250908105005.2119297-10-pbonzini@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

6 files changed, 33 insertions, 55 deletions

diff --git a/rust/hw/char/pl011/src/device.rs b/rust/hw/char/pl011/src/device.rs
index 87a17716fe..8411db8d00 100644
--- a/rust/hw/char/pl011/src/device.rs
+++ b/rust/hw/char/pl011/src/device.rs
@@ -172,9 +172,7 @@ impl ObjectImpl for PL011State {
 }
 
 impl DeviceImpl for PL011State {
-    fn vmsd() -> Option<VMStateDescription<Self>> {
-        Some(VMSTATE_PL011)
-    }
+    const VMSTATE: Option<VMStateDescription<Self>> = Some(VMSTATE_PL011);
     const REALIZE: Option<fn(&Self) -> qemu_api::Result<()>> = Some(Self::realize);
 }
 
diff --git a/rust/hw/timer/hpet/src/device.rs b/rust/hw/timer/hpet/src/device.rs
index eb5bd042b1..dd5326a40d 100644
--- a/rust/hw/timer/hpet/src/device.rs
+++ b/rust/hw/timer/hpet/src/device.rs
@@ -1008,16 +1008,11 @@ const VMSTATE_HPET: VMStateDescription<HPETState> =
 // SAFETY: HPET_PROPERTIES is a valid Property array constructed with the
 // qemu_api::declare_properties macro.
 unsafe impl qemu_api::qdev::DevicePropertiesImpl for HPETState {
-    fn properties() -> &'static [Property] {
-        &HPET_PROPERTIES
-    }
+    const PROPERTIES: &'static [Property] = &HPET_PROPERTIES;
 }
 
 impl DeviceImpl for HPETState {
-    fn vmsd() -> Option<VMStateDescription<Self>> {
-        Some(VMSTATE_HPET)
-    }
-
+    const VMSTATE: Option<VMStateDescription<Self>> = Some(VMSTATE_HPET);
     const REALIZE: Option<fn(&Self) -> qemu_api::Result<()>> = Some(Self::realize);
 }
 
diff --git a/rust/qemu-api-macros/src/lib.rs b/rust/qemu-api-macros/src/lib.rs
index 97b2c214b6..a65a7ce2fe 100644
--- a/rust/qemu-api-macros/src/lib.rs
+++ b/rust/qemu-api-macros/src/lib.rs
@@ -289,11 +289,9 @@ fn derive_device_or_error(input: DeriveInput) -> Result<proc_macro2::TokenStream
 
     Ok(quote_spanned! {input.span() =>
         unsafe impl ::qemu_api::qdev::DevicePropertiesImpl for #name {
-            fn properties() -> &'static [::qemu_api::bindings::Property] {
-                static PROPERTIES: &[::qemu_api::bindings::Property] = &[#(#properties_expanded),*];
-
-                PROPERTIES
-            }
+            const PROPERTIES: &'static [::qemu_api::bindings::Property] = &[
+                #(#properties_expanded),*
+            ];
         }
     })
 }
diff --git a/rust/qemu-api-macros/src/tests.rs b/rust/qemu-api-macros/src/tests.rs
index aafffcdce9..0e5a572890 100644
--- a/rust/qemu-api-macros/src/tests.rs
+++ b/rust/qemu-api-macros/src/tests.rs
@@ -101,18 +101,16 @@ fn test_derive_device() {
         },
         quote! {
             unsafe impl ::qemu_api::qdev::DevicePropertiesImpl for DummyState {
-                fn properties() -> &'static [::qemu_api::bindings::Property] {
-                    static PROPERTIES: &[::qemu_api::bindings::Property] =
-                        &[::qemu_api::bindings::Property {
-                            name: ::std::ffi::CStr::as_ptr(c"migrate_clock"),
-                            info: <bool as ::qemu_api::qdev::QDevProp>::VALUE,
-                            offset: ::core::mem::offset_of!(DummyState, migrate_clock) as isize,
-                            set_default: true,
-                            defval: ::qemu_api::bindings::Property__bindgen_ty_1 { u: true as u64 },
-                            ..::qemu_api::zeroable::Zeroable::ZERO
-                        }];
-                    PROPERTIES
-                }
+                const PROPERTIES: &'static [::qemu_api::bindings::Property] = &[
+                    ::qemu_api::bindings::Property {
+                        name: ::std::ffi::CStr::as_ptr(c"migrate_clock"),
+                        info: <bool as ::qemu_api::qdev::QDevProp>::VALUE,
+                        offset: ::core::mem::offset_of!(DummyState, migrate_clock) as isize,
+                        set_default: true,
+                        defval: ::qemu_api::bindings::Property__bindgen_ty_1 { u: true as u64 },
+                        ..::qemu_api::zeroable::Zeroable::ZERO
+                    }
+                ];
             }
         }
     );
@@ -130,18 +128,16 @@ fn test_derive_device() {
         },
         quote! {
             unsafe impl ::qemu_api::qdev::DevicePropertiesImpl for DummyState {
-                fn properties() -> &'static [::qemu_api::bindings::Property] {
-                    static PROPERTIES: &[::qemu_api::bindings::Property] =
-                        &[::qemu_api::bindings::Property {
-                            name: ::std::ffi::CStr::as_ptr(c"migrate-clk"),
-                            info: <bool as ::qemu_api::qdev::QDevProp>::VALUE,
-                            offset: ::core::mem::offset_of!(DummyState, migrate_clock) as isize,
-                            set_default: true,
-                            defval: ::qemu_api::bindings::Property__bindgen_ty_1 { u: true as u64 },
-                            ..::qemu_api::zeroable::Zeroable::ZERO
-                        }];
-                    PROPERTIES
-                }
+                const PROPERTIES: &'static [::qemu_api::bindings::Property] = &[
+                    ::qemu_api::bindings::Property {
+                        name: ::std::ffi::CStr::as_ptr(c"migrate-clk"),
+                        info: <bool as ::qemu_api::qdev::QDevProp>::VALUE,
+                        offset: ::core::mem::offset_of!(DummyState, migrate_clock) as isize,
+                        set_default: true,
+                        defval: ::qemu_api::bindings::Property__bindgen_ty_1 { u: true as u64 },
+                        ..::qemu_api::zeroable::Zeroable::ZERO
+                    }
+                ];
             }
         }
     );
diff --git a/rust/qemu-api/src/qdev.rs b/rust/qemu-api/src/qdev.rs
index 4dda8c8113..436142d8ae 100644
--- a/rust/qemu-api/src/qdev.rs
+++ b/rust/qemu-api/src/qdev.rs
@@ -151,11 +151,8 @@ unsafe impl QDevProp for crate::chardev::CharBackend {
 /// Caller is responsible for the validity of properties array.
 pub unsafe trait DevicePropertiesImpl {
     /// An array providing the properties that the user can set on the
-    /// device.  Not a `const` because referencing statics in constants
-    /// is unstable until Rust 1.83.0.
-    fn properties() -> &'static [Property] {
-        &[]
-    }
+    /// device.
+    const PROPERTIES: &'static [Property] = &[];
 }
 
 /// Trait providing the contents of [`DeviceClass`].
@@ -173,9 +170,7 @@ pub trait DeviceImpl:
     /// A `VMStateDescription` providing the migration format for the device
     /// Not a `const` because referencing statics in constants is unstable
     /// until Rust 1.83.0.
-    fn vmsd() -> Option<VMStateDescription<Self>> {
-        None
-    }
+    const VMSTATE: Option<VMStateDescription<Self>> = None;
 }
 
 /// # Safety
@@ -224,12 +219,10 @@ impl DeviceClass {
         if <T as DeviceImpl>::REALIZE.is_some() {
             self.realize = Some(rust_realize_fn::<T>);
         }
-        if let Some(vmsd) = <T as DeviceImpl>::vmsd() {
-            // Give a 'static lifetime to the return value of vmsd().
-            // Temporary until vmsd() can be changed into a const.
-            self.vmsd = Box::leak(Box::new(vmsd.get()));
+        if let Some(ref vmsd) = <T as DeviceImpl>::VMSTATE {
+            self.vmsd = vmsd.as_ref();
         }
-        let prop = <T as DevicePropertiesImpl>::properties();
+        let prop = <T as DevicePropertiesImpl>::PROPERTIES;
         if !prop.is_empty() {
             unsafe {
                 bindings::device_class_set_props_n(self, prop.as_ptr(), prop.len());
diff --git a/rust/qemu-api/tests/tests.rs b/rust/qemu-api/tests/tests.rs
index 4d4e4653f3..1349568741 100644
--- a/rust/qemu-api/tests/tests.rs
+++ b/rust/qemu-api/tests/tests.rs
@@ -56,9 +56,7 @@ impl ObjectImpl for DummyState {
 impl ResettablePhasesImpl for DummyState {}
 
 impl DeviceImpl for DummyState {
-    fn vmsd() -> Option<VMStateDescription<Self>> {
-        Some(VMSTATE)
-    }
+    const VMSTATE: Option<VMStateDescription<Self>> = Some(VMSTATE);
 }
 
 #[repr(C)]