[RFC PATCH 2/9] rust: vmstate: implement VMState for non-leaf types

[Paolo Bonzini <pbonzini@redhat.com>]

Arrays, pointers and cells use a VMStateField that is based on that
for the inner type.  The implementation therefore delegates to the
VMState implementation of the inner type.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/qemu-api/src/vmstate.rs | 66 +++++++++++++++++++++++++++++++++++-
 1 file changed, 65 insertions(+), 1 deletion(-)

diff --git a/rust/qemu-api/src/vmstate.rs b/rust/qemu-api/src/vmstate.rs
index bfcf06e8f1d..e20f27b172b 100644
--- a/rust/qemu-api/src/vmstate.rs
+++ b/rust/qemu-api/src/vmstate.rs
@@ -19,8 +19,9 @@
 //!   `include/migration/vmstate.h`. These are not type-safe and should not be
 //!   used if the equivalent functionality is available with `vmstate_of!`.
 
-use core::marker::PhantomData;
+use core::{marker::PhantomData, mem, ptr::NonNull};
 
+use crate::bindings::VMStateFlags;
 pub use crate::bindings::{VMStateDescription, VMStateField};
 
 /// This macro is used to call a function with a generic argument bound
@@ -108,6 +109,69 @@ pub const fn with_version_id(mut self, version_id: i32) -> Self {
         self.version_id = version_id;
         self
     }
+
+    #[must_use]
+    pub const fn with_array_flag(mut self, num: usize) -> Self {
+        assert!(num <= 0x7FFF_FFFFusize);
+        assert!((self.flags.0 & VMStateFlags::VMS_ARRAY.0) == 0);
+        if (self.flags.0 & VMStateFlags::VMS_POINTER.0) != 0 {
+            self.flags = VMStateFlags(self.flags.0 & !VMStateFlags::VMS_POINTER.0);
+            self.flags = VMStateFlags(self.flags.0 | VMStateFlags::VMS_ARRAY_OF_POINTER.0);
+        }
+        self.flags = VMStateFlags(self.flags.0 & !VMStateFlags::VMS_SINGLE.0);
+        self.flags = VMStateFlags(self.flags.0 | VMStateFlags::VMS_ARRAY.0);
+        self.num = num as i32;
+        self
+    }
+
+    #[must_use]
+    pub const fn with_pointer_flag(mut self) -> Self {
+        assert!((self.flags.0 & VMStateFlags::VMS_POINTER.0) == 0);
+        self.flags = VMStateFlags(self.flags.0 | VMStateFlags::VMS_POINTER.0);
+        self
+    }
+}
+
+// Transparent wrappers: just use the internal type
+
+macro_rules! impl_vmstate_transparent {
+    ($type:ty where $base:tt: VMState $($where:tt)*) => {
+        unsafe impl<$base> VMState for $type where $base: VMState $($where)* {
+            const BASE: VMStateField = VMStateField {
+                size: mem::size_of::<$type>(),
+                ..<$base as VMState>::BASE
+            };
+        }
+    };
+}
+
+impl_vmstate_transparent!(std::cell::Cell<T> where T: VMState);
+impl_vmstate_transparent!(std::cell::UnsafeCell<T> where T: VMState);
+impl_vmstate_transparent!(crate::cell::BqlCell<T> where T: VMState);
+impl_vmstate_transparent!(crate::cell::BqlRefCell<T> where T: VMState);
+
+// Pointer types using the underlying type's VMState plus VMS_POINTER
+
+macro_rules! impl_vmstate_pointer {
+    ($type:ty where $base:tt: VMState $($where:tt)*) => {
+        unsafe impl<$base> VMState for $type where $base: VMState $($where)* {
+            const SCALAR_TYPE: VMStateFieldType = <T as VMState>::SCALAR_TYPE;
+            const BASE: VMStateField = <$base as VMState>::BASE.with_pointer_flag();
+        }
+    };
+}
+
+impl_vmstate_pointer!(*const T where T: VMState);
+impl_vmstate_pointer!(*mut T where T: VMState);
+impl_vmstate_pointer!(NonNull<T> where T: VMState);
+impl_vmstate_pointer!(Option<NonNull<T>> where T: VMState);
+
+// Arrays using the underlying type's VMState plus
+// VMS_ARRAY/VMS_ARRAY_OF_POINTER
+
+unsafe impl<T: VMState, const N: usize> VMState for [T; N] {
+    const SCALAR_TYPE: VMStateFieldType = <T as VMState>::SCALAR_TYPE;
+    const BASE: VMStateField = <T as VMState>::BASE.with_array_flag(N);
 }
 
 #[doc(alias = "VMSTATE_UNUSED_BUFFER")]
-- 
2.47.1