@@ -349,68 +349,70 @@ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
}
}
-impl<T: 'static, A> ForeignOwnable for Box<T, A>
+// SAFETY: The `into_foreign` function returns a pointer that is well-aligned.
+unsafe impl<T: 'static, A> ForeignOwnable for Box<T, A>
where
A: Allocator,
{
+ type PointedTo = T;
type Borrowed<'a> = &'a T;
type BorrowedMut<'a> = &'a mut T;
- fn into_foreign(self) -> *mut crate::ffi::c_void {
- Box::into_raw(self).cast()
+ fn into_foreign(self) -> *mut Self::PointedTo {
+ Box::into_raw(self)
}
- unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self {
+ unsafe fn from_foreign(ptr: *mut Self::PointedTo) -> Self {
// SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
// call to `Self::into_foreign`.
- unsafe { Box::from_raw(ptr.cast()) }
+ unsafe { Box::from_raw(ptr) }
}
- unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> &'a T {
+ unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> &'a T {
// SAFETY: The safety requirements of this method ensure that the object remains alive and
// immutable for the duration of 'a.
- unsafe { &*ptr.cast() }
+ unsafe { &*ptr }
}
- unsafe fn borrow_mut<'a>(ptr: *mut core::ffi::c_void) -> &'a mut T {
- let ptr = ptr.cast();
+ unsafe fn borrow_mut<'a>(ptr: *mut Self::PointedTo) -> &'a mut T {
// SAFETY: The safety requirements of this method ensure that the pointer is valid and that
// nothing else will access the value for the duration of 'a.
unsafe { &mut *ptr }
}
}
-impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>
+// SAFETY: The `into_foreign` function returns a pointer that is well-aligned.
+unsafe impl<T: 'static, A> ForeignOwnable for Pin<Box<T, A>>
where
A: Allocator,
{
+ type PointedTo = T;
type Borrowed<'a> = Pin<&'a T>;
type BorrowedMut<'a> = Pin<&'a mut T>;
- fn into_foreign(self) -> *mut crate::ffi::c_void {
+ fn into_foreign(self) -> *mut Self::PointedTo {
// SAFETY: We are still treating the box as pinned.
- Box::into_raw(unsafe { Pin::into_inner_unchecked(self) }).cast()
+ Box::into_raw(unsafe { Pin::into_inner_unchecked(self) })
}
- unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self {
+ unsafe fn from_foreign(ptr: *mut Self::PointedTo) -> Self {
// SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
// call to `Self::into_foreign`.
- unsafe { Pin::new_unchecked(Box::from_raw(ptr.cast())) }
+ unsafe { Pin::new_unchecked(Box::from_raw(ptr)) }
}
- unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> Pin<&'a T> {
+ unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> Pin<&'a T> {
// SAFETY: The safety requirements for this function ensure that the object is still alive,
// so it is safe to dereference the raw pointer.
// The safety requirements of `from_foreign` also ensure that the object remains alive for
// the lifetime of the returned value.
- let r = unsafe { &*ptr.cast() };
+ let r = unsafe { &*ptr };
// SAFETY: This pointer originates from a `Pin<Box<T>>`.
unsafe { Pin::new_unchecked(r) }
}
- unsafe fn borrow_mut<'a>(ptr: *mut core::ffi::c_void) -> Pin<&'a mut T> {
- let ptr = ptr.cast();
+ unsafe fn borrow_mut<'a>(ptr: *mut Self::PointedTo) -> Pin<&'a mut T> {
// SAFETY: The safety requirements for this function ensure that the object is still alive,
// so it is safe to dereference the raw pointer.
// The safety requirements of `from_foreign` also ensure that the object remains alive for
@@ -193,7 +193,7 @@ impl<T: MiscDevice> VtableHelper<T> {
};
// SAFETY: The open call of a file owns the private data.
- unsafe { (*file).private_data = ptr.into_foreign() };
+ unsafe { (*file).private_data = ptr.into_foreign().cast() };
0
}
@@ -209,7 +209,7 @@ impl<T: MiscDevice> VtableHelper<T> {
// SAFETY: The release call of a file owns the private data.
let private = unsafe { (*file).private_data };
// SAFETY: The release call of a file owns the private data.
- let ptr = unsafe { <T::Ptr as ForeignOwnable>::from_foreign(private) };
+ let ptr = unsafe { <T::Ptr as ForeignOwnable>::from_foreign(private.cast()) };
T::release(ptr);
@@ -227,7 +227,7 @@ impl<T: MiscDevice> VtableHelper<T> {
// SAFETY: The ioctl call of a file can access the private data.
let private = unsafe { (*file).private_data };
// SAFETY: Ioctl calls can borrow the private data of the file.
- let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
+ let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private.cast()) };
match T::ioctl(device, cmd, arg as usize) {
Ok(ret) => ret as c_long,
@@ -130,9 +130,10 @@ pub struct Arc<T: ?Sized> {
_p: PhantomData<ArcInner<T>>,
}
+#[doc(hidden)]
#[pin_data]
#[repr(C)]
-struct ArcInner<T: ?Sized> {
+pub struct ArcInner<T: ?Sized> {
refcount: Opaque<bindings::refcount_t>,
data: T,
}
@@ -330,18 +331,20 @@ pub fn into_unique_or_drop(self) -> Option<Pin<UniqueArc<T>>> {
}
}
-impl<T: 'static> ForeignOwnable for Arc<T> {
+// SAFETY: The `into_foreign` function returns a pointer that is well-aligned.
+unsafe impl<T: 'static> ForeignOwnable for Arc<T> {
+ type PointedTo = ArcInner<T>;
type Borrowed<'a> = ArcBorrow<'a, T>;
type BorrowedMut<'a> = Self::Borrowed<'a>;
- fn into_foreign(self) -> *mut crate::ffi::c_void {
- ManuallyDrop::new(self).ptr.as_ptr().cast()
+ fn into_foreign(self) -> *mut Self::PointedTo {
+ ManuallyDrop::new(self).ptr.as_ptr()
}
- unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self {
+ unsafe fn from_foreign(ptr: *mut Self::PointedTo) -> Self {
// SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
// call to `Self::into_foreign`.
- let inner = unsafe { NonNull::new_unchecked(ptr.cast::<ArcInner<T>>()) };
+ let inner = unsafe { NonNull::new_unchecked(ptr) };
// SAFETY: By the safety requirement of this function, we know that `ptr` came from
// a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
@@ -349,17 +352,17 @@ unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self {
unsafe { Self::from_inner(inner) }
}
- unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> ArcBorrow<'a, T> {
+ unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> ArcBorrow<'a, T> {
// SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
// call to `Self::into_foreign`.
- let inner = unsafe { NonNull::new_unchecked(ptr.cast::<ArcInner<T>>()) };
+ let inner = unsafe { NonNull::new_unchecked(ptr) };
// SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
// for the lifetime of the returned value.
unsafe { ArcBorrow::new(inner) }
}
- unsafe fn borrow_mut<'a>(ptr: *mut core::ffi::c_void) -> ArcBorrow<'a, T> {
+ unsafe fn borrow_mut<'a>(ptr: *mut Self::PointedTo) -> ArcBorrow<'a, T> {
// SAFETY: The safety requirements for `borrow_mut` are a superset of the safety
// requirements for `borrow`.
unsafe { Self::borrow(ptr) }
@@ -18,7 +18,19 @@
///
/// This trait is meant to be used in cases when Rust objects are stored in C objects and
/// eventually "freed" back to Rust.
-pub trait ForeignOwnable: Sized {
+///
+/// # Safety
+///
+/// Implementers must ensure that [`into_foreign`] returns a pointer which meets the alignment
+/// requirements of [`PointedTo`].
+///
+/// [`into_foreign`]: Self::into_foreign
+/// [`PointedTo`]: Self::PointedTo
+pub unsafe trait ForeignOwnable: Sized {
+ /// Type used when the value is foreign-owned. In practical terms only defines the alignment of
+ /// the pointer.
+ type PointedTo;
+
/// Type used to immutably borrow a value that is currently foreign-owned.
type Borrowed<'a>;
@@ -27,16 +39,18 @@ pub trait ForeignOwnable: Sized {
/// Converts a Rust-owned object to a foreign-owned one.
///
- /// The foreign representation is a pointer to void. There are no guarantees for this pointer.
- /// For example, it might be invalid, dangling or pointing to uninitialized memory. Using it in
- /// any way except for [`from_foreign`], [`try_from_foreign`], [`borrow`], or [`borrow_mut`] can
- /// result in undefined behavior.
+ /// # Guarantees
+ ///
+ /// The return value is guaranteed to be well-aligned, but there are no other guarantees for
+ /// this pointer. For example, it might be null, dangling, or point to uninitialized memory.
+ /// Using it in any way except for [`ForeignOwnable::from_foreign`], [`ForeignOwnable::borrow`],
+ /// [`ForeignOwnable::try_from_foreign`] can result in undefined behavior.
///
/// [`from_foreign`]: Self::from_foreign
/// [`try_from_foreign`]: Self::try_from_foreign
/// [`borrow`]: Self::borrow
/// [`borrow_mut`]: Self::borrow_mut
- fn into_foreign(self) -> *mut crate::ffi::c_void;
+ fn into_foreign(self) -> *mut Self::PointedTo;
/// Converts a foreign-owned object back to a Rust-owned one.
///
@@ -46,7 +60,7 @@ pub trait ForeignOwnable: Sized {
/// must not be passed to `from_foreign` more than once.
///
/// [`into_foreign`]: Self::into_foreign
- unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self;
+ unsafe fn from_foreign(ptr: *mut Self::PointedTo) -> Self;
/// Tries to convert a foreign-owned object back to a Rust-owned one.
///
@@ -58,7 +72,7 @@ pub trait ForeignOwnable: Sized {
/// `ptr` must either be null or satisfy the safety requirements for [`from_foreign`].
///
/// [`from_foreign`]: Self::from_foreign
- unsafe fn try_from_foreign(ptr: *mut crate::ffi::c_void) -> Option<Self> {
+ unsafe fn try_from_foreign(ptr: *mut Self::PointedTo) -> Option<Self> {
if ptr.is_null() {
None
} else {
@@ -81,7 +95,7 @@ unsafe fn try_from_foreign(ptr: *mut crate::ffi::c_void) -> Option<Self> {
///
/// [`into_foreign`]: Self::into_foreign
/// [`from_foreign`]: Self::from_foreign
- unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> Self::Borrowed<'a>;
+ unsafe fn borrow<'a>(ptr: *mut Self::PointedTo) -> Self::Borrowed<'a>;
/// Borrows a foreign-owned object mutably.
///
@@ -109,21 +123,23 @@ unsafe fn try_from_foreign(ptr: *mut crate::ffi::c_void) -> Option<Self> {
/// [`from_foreign`]: Self::from_foreign
/// [`borrow`]: Self::borrow
/// [`Arc`]: crate::sync::Arc
- unsafe fn borrow_mut<'a>(ptr: *mut crate::ffi::c_void) -> Self::BorrowedMut<'a>;
+ unsafe fn borrow_mut<'a>(ptr: *mut Self::PointedTo) -> Self::BorrowedMut<'a>;
}
-impl ForeignOwnable for () {
+// SAFETY: The `into_foreign` function returns a pointer that is dangling, but well-aligned.
+unsafe impl ForeignOwnable for () {
+ type PointedTo = ();
type Borrowed<'a> = ();
type BorrowedMut<'a> = ();
- fn into_foreign(self) -> *mut crate::ffi::c_void {
+ fn into_foreign(self) -> *mut Self::PointedTo {
core::ptr::NonNull::dangling().as_ptr()
}
- unsafe fn from_foreign(_: *mut crate::ffi::c_void) -> Self {}
+ unsafe fn from_foreign(_: *mut Self::PointedTo) -> Self {}
- unsafe fn borrow<'a>(_: *mut crate::ffi::c_void) -> Self::Borrowed<'a> {}
- unsafe fn borrow_mut<'a>(_: *mut crate::ffi::c_void) -> Self::BorrowedMut<'a> {}
+ unsafe fn borrow<'a>(_: *mut Self::PointedTo) -> Self::Borrowed<'a> {}
+ unsafe fn borrow_mut<'a>(_: *mut Self::PointedTo) -> Self::BorrowedMut<'a> {}
}
/// Runs a cleanup function/closure when dropped.