rust: split Rust-only "common" crate

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Link: https://lore.kernel.org/r/20250827104147.717203-6-marcandre.lureau@redhat.com
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 2 insertions, 233 deletions

diff --git a/rust/qemu-api/src/cell.rs b/rust/qemu-api/src/cell.rs
index 9943d72..d13848d 100644
--- a/rust/qemu-api/src/cell.rs
+++ b/rust/qemu-api/src/cell.rs
@@ -141,82 +141,13 @@
 //! Multiple immutable borrows are allowed via [`borrow`](BqlRefCell::borrow),
 //! or a single mutable borrow via [`borrow_mut`](BqlRefCell::borrow_mut).  The
 //! thread will panic if these rules are violated or if the BQL is not held.
-//!
-//! ## Opaque wrappers
-//!
-//! The cell types from the previous section are useful at the boundaries
-//! of code that requires interior mutability.  When writing glue code that
-//! interacts directly with C structs, however, it is useful to operate
-//! at a lower level.
-//!
-//! C functions often violate Rust's fundamental assumptions about memory
-//! safety by modifying memory even if it is shared.  Furthermore, C structs
-//! often start their life uninitialized and may be populated lazily.
-//!
-//! For this reason, this module provides the [`Opaque<T>`] type to opt out
-//! of Rust's usual guarantees about the wrapped type. Access to the wrapped
-//! value is always through raw pointers, obtained via methods like
-//! [`as_mut_ptr()`](Opaque::as_mut_ptr) and [`as_ptr()`](Opaque::as_ptr). These
-//! pointers can then be passed to C functions or dereferenced; both actions
-//! require `unsafe` blocks, making it clear where safety guarantees must be
-//! manually verified. For example
-//!
-//! ```ignore
-//! unsafe {
-//!     let state = Opaque::<MyStruct>::uninit();
-//!     qemu_struct_init(state.as_mut_ptr());
-//! }
-//! ```
-//!
-//! [`Opaque<T>`] will usually be wrapped one level further, so that
-//! bridge methods can be added to the wrapper:
-//!
-//! ```ignore
-//! pub struct MyStruct(Opaque<bindings::MyStruct>);
-//!
-//! impl MyStruct {
-//!     fn new() -> Pin<Box<MyStruct>> {
-//!         let result = Box::pin(unsafe { Opaque::uninit() });
-//!         unsafe { qemu_struct_init(result.as_mut_ptr()) };
-//!         result
-//!     }
-//! }
-//! ```
-//!
-//! This pattern of wrapping bindgen-generated types in [`Opaque<T>`] provides
-//! several advantages:
-//!
-//! * The choice of traits to be implemented is not limited by the
-//!   bindgen-generated code.  For example, [`Drop`] can be added without
-//!   disabling [`Copy`] on the underlying bindgen type
-//!
-//! * [`Send`] and [`Sync`] implementations can be controlled by the wrapper
-//!   type rather than being automatically derived from the C struct's layout
-//!
-//! * Methods can be implemented in a separate crate from the bindgen-generated
-//!   bindings
-//!
-//! * [`Debug`](std::fmt::Debug) and [`Display`](std::fmt::Display)
-//!   implementations can be customized to be more readable than the raw C
-//!   struct representation
-//!
-//! The [`Opaque<T>`] type does not include BQL validation; it is possible to
-//! assert in the code that the right lock is taken, to use it together
-//! with a custom lock guard type, or to let C code take the lock, as
-//! appropriate.  It is also possible to use it with non-thread-safe
-//! types, since by default (unlike [`BqlCell`] and [`BqlRefCell`]
-//! it is neither `Sync` nor `Send`.
-//!
-//! While [`Opaque<T>`] is necessary for C interop, it should be used sparingly
-//! and only at FFI boundaries. For QEMU-specific types that need interior
-//! mutability, prefer [`BqlCell`] or [`BqlRefCell`].
 
 use std::{
     cell::{Cell, UnsafeCell},
     cmp::Ordering,
     fmt,
-    marker::{PhantomData, PhantomPinned},
-    mem::{self, MaybeUninit},
+    marker::PhantomData,
+    mem,
     ops::{Deref, DerefMut},
     ptr::NonNull,
 };
@@ -939,165 +870,3 @@ impl<T: fmt::Display> fmt::Display for BqlRefMut<'_, T> {
         (**self).fmt(f)
     }
 }
-
-/// Stores an opaque value that is shared with C code.
-///
-/// Often, C structs can changed when calling a C function even if they are
-/// behind a shared Rust reference, or they can be initialized lazily and have
-/// invalid bit patterns (e.g. `3` for a [`bool`]).  This goes against Rust's
-/// strict aliasing rules, which normally prevent mutation through shared
-/// references.
-///
-/// Wrapping the struct with `Opaque<T>` ensures that the Rust compiler does not
-/// assume the usual constraints that Rust structs require, and allows using
-/// shared references on the Rust side.
-///
-/// `Opaque<T>` is `#[repr(transparent)]`, so that it matches the memory layout
-/// of `T`.
-#[repr(transparent)]
-pub struct Opaque<T> {
-    value: UnsafeCell<MaybeUninit<T>>,
-    // PhantomPinned also allows multiple references to the `Opaque<T>`, i.e.
-    // one `&mut Opaque<T>` can coexist with a `&mut T` or any number of `&T`;
-    // see https://docs.rs/pinned-aliasable/latest/pinned_aliasable/.
-    _pin: PhantomPinned,
-}
-
-impl<T> Opaque<T> {
-    /// Creates a new shared reference from a C pointer
-    ///
-    /// # Safety
-    ///
-    /// The pointer must be valid, though it need not point to a valid value.
-    pub unsafe fn from_raw<'a>(ptr: *mut T) -> &'a Self {
-        let ptr = NonNull::new(ptr).unwrap().cast::<Self>();
-        // SAFETY: Self is a transparent wrapper over T
-        unsafe { ptr.as_ref() }
-    }
-
-    /// Creates a new opaque object with uninitialized contents.
-    ///
-    /// # Safety
-    ///
-    /// Ultimately the pointer to the returned value will be dereferenced
-    /// in another `unsafe` block, for example when passing it to a C function,
-    /// but the functions containing the dereference are usually safe.  The
-    /// value returned from `uninit()` must be initialized and pinned before
-    /// calling them.
-    pub const unsafe fn uninit() -> Self {
-        Self {
-            value: UnsafeCell::new(MaybeUninit::uninit()),
-            _pin: PhantomPinned,
-        }
-    }
-
-    /// Creates a new opaque object with zeroed contents.
-    ///
-    /// # Safety
-    ///
-    /// Ultimately the pointer to the returned value will be dereferenced
-    /// in another `unsafe` block, for example when passing it to a C function,
-    /// but the functions containing the dereference are usually safe.  The
-    /// value returned from `uninit()` must be pinned (and possibly initialized)
-    /// before calling them.
-    pub const unsafe fn zeroed() -> Self {
-        Self {
-            value: UnsafeCell::new(MaybeUninit::zeroed()),
-            _pin: PhantomPinned,
-        }
-    }
-
-    /// Returns a raw mutable pointer to the opaque data.
-    pub const fn as_mut_ptr(&self) -> *mut T {
-        UnsafeCell::get(&self.value).cast()
-    }
-
-    /// Returns a raw pointer to the opaque data.
-    pub const fn as_ptr(&self) -> *const T {
-        self.as_mut_ptr().cast_const()
-    }
-
-    /// Returns a raw pointer to the opaque data that can be passed to a
-    /// C function as `void *`.
-    pub const fn as_void_ptr(&self) -> *mut std::ffi::c_void {
-        UnsafeCell::get(&self.value).cast()
-    }
-
-    /// Converts a raw pointer to the wrapped type.
-    pub const fn raw_get(slot: *mut Self) -> *mut T {
-        // Compare with Linux's raw_get method, which goes through an UnsafeCell
-        // because it takes a *const Self instead.
-        slot.cast()
-    }
-}
-
-impl<T> fmt::Debug for Opaque<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let mut name: String = "Opaque<".to_string();
-        name += std::any::type_name::<T>();
-        name += ">";
-        f.debug_tuple(&name).field(&self.as_ptr()).finish()
-    }
-}
-
-impl<T: Default> Opaque<T> {
-    /// Creates a new opaque object with default contents.
-    ///
-    /// # Safety
-    ///
-    /// Ultimately the pointer to the returned value will be dereferenced
-    /// in another `unsafe` block, for example when passing it to a C function,
-    /// but the functions containing the dereference are usually safe.  The
-    /// value returned from `uninit()` must be pinned before calling them.
-    pub unsafe fn new() -> Self {
-        Self {
-            value: UnsafeCell::new(MaybeUninit::new(T::default())),
-            _pin: PhantomPinned,
-        }
-    }
-}
-
-/// Annotates [`Self`] as a transparent wrapper for another type.
-///
-/// Usually defined via the [`qemu_api_macros::Wrapper`] derive macro.
-///
-/// # Examples
-///
-/// ```
-/// # use std::mem::ManuallyDrop;
-/// # use qemu_api::cell::Wrapper;
-/// #[repr(transparent)]
-/// pub struct Example {
-///     inner: ManuallyDrop<String>,
-/// }
-///
-/// unsafe impl Wrapper for Example {
-///     type Wrapped = String;
-/// }
-/// ```
-///
-/// # Safety
-///
-/// `Self` must be a `#[repr(transparent)]` wrapper for the `Wrapped` type,
-/// whether directly or indirectly.
-///
-/// # Methods
-///
-/// By convention, types that implement Wrapper also implement the following
-/// methods:
-///
-/// ```ignore
-/// pub const unsafe fn from_raw<'a>(value: *mut Self::Wrapped) -> &'a Self;
-/// pub const unsafe fn as_mut_ptr(&self) -> *mut Self::Wrapped;
-/// pub const unsafe fn as_ptr(&self) -> *const Self::Wrapped;
-/// pub const unsafe fn raw_get(slot: *mut Self) -> *const Self::Wrapped;
-/// ```
-///
-/// They are not defined here to allow them to be `const`.
-pub unsafe trait Wrapper {
-    type Wrapped;
-}
-
-unsafe impl<T> Wrapper for Opaque<T> {
-    type Wrapped = T;
-}