[PATCH] rust: qom: remove operations on &mut

[Paolo Bonzini <pbonzini@redhat.com>]

The dubious casts of mutable references to objects are not used
anymore: the wrappers for qdev_init_clock_in and for IRQ and MMIO
initialization can be called directly on the subclasses, without
casts, plus they take a shared reference so they can just use
"upcast()" instead of "upcast_mut()".  Remove them.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/qemu-api/src/prelude.rs |  1 -
 rust/qemu-api/src/qom.rs     | 83 ------------------------------------
 rust/qemu-api/tests/tests.rs | 34 +--------------
 3 files changed, 2 insertions(+), 116 deletions(-)

diff --git a/rust/qemu-api/src/prelude.rs b/rust/qemu-api/src/prelude.rs
index 634acf37a85..43bfcd5fcab 100644
--- a/rust/qemu-api/src/prelude.rs
+++ b/rust/qemu-api/src/prelude.rs
@@ -17,7 +17,6 @@
 pub use crate::qom::IsA;
 pub use crate::qom::Object;
 pub use crate::qom::ObjectCast;
-pub use crate::qom::ObjectCastMut;
 pub use crate::qom::ObjectDeref;
 pub use crate::qom::ObjectClassMethods;
 pub use crate::qom::ObjectMethods;
diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs
index 2defbd23516..34d7bc0ef96 100644
--- a/rust/qemu-api/src/qom.rs
+++ b/rust/qemu-api/src/qom.rs
@@ -463,90 +463,7 @@ unsafe fn unsafe_cast<'a, U: ObjectType>(self) -> &'a U
 impl<T: ObjectType> ObjectDeref for &T {}
 impl<T: ObjectType> ObjectCast for &T {}
 
-/// Trait for mutable type casting operations in the QOM hierarchy.
-///
-/// This trait provides the mutable counterparts to [`ObjectCast`]'s conversion
-/// functions. Unlike `ObjectCast`, this trait returns `Result` for fallible
-/// conversions to preserve the original smart pointer if the cast fails. This
-/// is necessary because mutable references cannot be copied, so a failed cast
-/// must return ownership of the original reference. For example:
-///
-/// ```ignore
-/// let mut dev = get_device();
-/// // If this fails, we need the original `dev` back to try something else
-/// match dev.dynamic_cast_mut::<FooDevice>() {
-///    Ok(foodev) => /* use foodev */,
-///    Err(dev) => /* still have ownership of dev */
-/// }
-/// ```
-pub trait ObjectCastMut: Sized + ObjectDeref + DerefMut
-where
-    Self::Target: ObjectType,
-{
-    /// Safely convert from a derived type to one of its parent types.
-    ///
-    /// This is always safe; the [`IsA`] trait provides static verification
-    /// that `Self` dereferences to `U` or a child of `U`.
-    fn upcast_mut<'a, U: ObjectType>(self) -> &'a mut U
-    where
-        Self::Target: IsA<U>,
-        Self: 'a,
-    {
-        // SAFETY: soundness is declared via IsA<U>, which is an unsafe trait
-        unsafe { self.unsafe_cast_mut::<U>() }
-    }
-
-    /// Attempt to convert to a derived type.
-    ///
-    /// Returns `Ok(..)` if the object is of type `U`, or `Err(self)` if the
-    /// object if the conversion failed. This is verified at runtime by
-    /// checking the object's type information.
-    fn downcast_mut<'a, U: IsA<Self::Target>>(self) -> Result<&'a mut U, Self>
-    where
-        Self: 'a,
-    {
-        self.dynamic_cast_mut::<U>()
-    }
-
-    /// Attempt to convert between any two types in the QOM hierarchy.
-    ///
-    /// Returns `Ok(..)` if the object is of type `U`, or `Err(self)` if the
-    /// object if the conversion failed. This is verified at runtime by
-    /// checking the object's type information.
-    fn dynamic_cast_mut<'a, U: ObjectType>(self) -> Result<&'a mut U, Self>
-    where
-        Self: 'a,
-    {
-        unsafe {
-            // SAFETY: upcasting to Object is always valid, and the
-            // return type is either NULL or the argument itself
-            let result: *mut U =
-                object_dynamic_cast(self.as_object_mut_ptr(), U::TYPE_NAME.as_ptr()).cast();
-
-            result.as_mut().ok_or(self)
-        }
-    }
-
-    /// Convert to any QOM type without verification.
-    ///
-    /// # Safety
-    ///
-    /// What safety? You need to know yourself that the cast is correct; only
-    /// use when performance is paramount.  It is still better than a raw
-    /// pointer `cast()`, which does not even check that you remain in the
-    /// realm of QOM `ObjectType`s.
-    ///
-    /// `unsafe_cast::<Object>()` is always safe.
-    unsafe fn unsafe_cast_mut<'a, U: ObjectType>(self) -> &'a mut U
-    where
-        Self: 'a,
-    {
-        unsafe { &mut *self.as_mut_ptr::<Self::Target>().cast::<U>() }
-    }
-}
-
 impl<T: ObjectType> ObjectDeref for &mut T {}
-impl<T: ObjectType> ObjectCastMut for &mut T {}
 
 /// Trait a type must implement to be registered with QEMU.
 pub trait ObjectImpl: ObjectType + IsA<Object> {
diff --git a/rust/qemu-api/tests/tests.rs b/rust/qemu-api/tests/tests.rs
index e3985782a38..269122e7ec1 100644
--- a/rust/qemu-api/tests/tests.rs
+++ b/rust/qemu-api/tests/tests.rs
@@ -2,13 +2,10 @@
 // Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-use std::{
-    ffi::{c_void, CStr},
-    ptr::{addr_of, addr_of_mut},
-};
+use std::{ffi::CStr, ptr::addr_of};
 
 use qemu_api::{
-    bindings::{module_call_init, module_init_type, object_new, object_unref, qdev_prop_bool},
+    bindings::{module_call_init, module_init_type, qdev_prop_bool},
     c_str,
     cell::{self, BqlCell},
     declare_properties, define_property,
@@ -182,30 +179,3 @@ fn test_cast() {
         assert_eq!(addr_of!(*sbd_ref), p_ptr.cast());
     }
 }
-
-#[test]
-#[allow(clippy::shadow_unrelated)]
-/// Test casts on mutable references.
-fn test_cast_mut() {
-    init_qom();
-    let p: *mut DummyState = unsafe { object_new(DummyState::TYPE_NAME.as_ptr()).cast() };
-
-    let p_ref: &mut DummyState = unsafe { &mut *p };
-    let obj_ref: &mut Object = p_ref.upcast_mut();
-    assert_eq!(addr_of_mut!(*obj_ref), p.cast());
-
-    let sbd_ref: Result<&mut SysBusDevice, &mut Object> = obj_ref.dynamic_cast_mut();
-    let obj_ref = sbd_ref.unwrap_err();
-
-    let dev_ref: Result<&mut DeviceState, &mut Object> = obj_ref.downcast_mut();
-    let dev_ref = dev_ref.unwrap();
-    assert_eq!(addr_of_mut!(*dev_ref), p.cast());
-
-    // SAFETY: the cast is wrong, but the value is only used for comparison
-    unsafe {
-        let sbd_ref: &mut SysBusDevice = obj_ref.unsafe_cast_mut();
-        assert_eq!(addr_of_mut!(*sbd_ref), p.cast());
-
-        object_unref(p_ref.as_object_mut_ptr().cast::<c_void>());
-    }
-}
-- 
2.48.1