Messages in this thread | | | Date | Fri, 20 Jan 2023 11:59:29 -0800 | From | Boqun Feng <> | Subject | Re: [PATCH 2/5] rust: types: introduce `ForeignOwnable` |
| |
On Thu, Jan 19, 2023 at 02:40:33PM -0300, Wedson Almeida Filho wrote: > It was originally called `PointerWrapper`. It is used to convert > a Rust object to a pointer representation (void *) that can be > stored on the C side, used, and eventually returned to Rust. > > Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com> > --- > rust/kernel/lib.rs | 1 + > rust/kernel/types.rs | 54 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 55 insertions(+) > > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index e0b0e953907d..223564f9f0cc 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -16,6 +16,7 @@ > #![feature(coerce_unsized)] > #![feature(core_ffi_c)] > #![feature(dispatch_from_dyn)] > +#![feature(generic_associated_types)] > #![feature(receiver_trait)] > #![feature(unsize)] > > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs > index f0ad4472292d..5475f6163002 100644 > --- a/rust/kernel/types.rs > +++ b/rust/kernel/types.rs > @@ -9,6 +9,60 @@ use core::{ > ops::{Deref, DerefMut}, > }; > > +/// Used to transfer ownership to and from foreign (non-Rust) languages. > +/// > +/// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and > +/// later may be transferred back to Rust by calling [`Self::from_foreign`]. > +/// > +/// 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 { > + /// Type of values borrowed between calls to [`ForeignOwnable::into_foreign`] and > + /// [`ForeignOwnable::from_foreign`]. > + type Borrowed<'a>; > + > + /// Converts a Rust-owned object to a foreign-owned one. > + /// > + /// The foreign representation is a pointer to void. > + fn into_foreign(self) -> *const core::ffi::c_void; > + > + /// Borrows a foreign-owned object. > + /// > + /// # Safety > + /// > + /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for > + /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet. > + /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow_mut`] > + /// for this object must have been dropped. > + unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>; > + > + /// Mutably borrows a foreign-owned object. > + /// > + /// # Safety > + /// > + /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for > + /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet. > + /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and > + /// [`ForeignOwnable::borrow_mut`] for this object must have been dropped. > + unsafe fn borrow_mut<T: ForeignOwnable>(ptr: *const core::ffi::c_void) -> ScopeGuard<T, fn(T)> { > + // SAFETY: The safety requirements ensure that `ptr` came from a previous call to > + // `into_foreign`. > + ScopeGuard::new_with_data(unsafe { T::from_foreign(ptr) }, |d| { > + d.into_foreign(); > + })
I kinda want to suggest borrow_mut() to be implemented as:
pub trait ForeignOwnable { ... unsafe fn borrow_mut(ptr: *const core::ffi::c_void) -> ScopeGuard<Self, fn(Self)> { // SAFETY: The safety requirements ensure that `ptr` came from a previous call to // `into_foreign`. ScopeGuard::new_with_data(unsafe { Self::from_foreign(ptr) }, |d| { d.into_foreign(); }) }
to avoid funny code as follow:
let a = Box::new(0).into_foreign(); // Using an irrelevant `impl ForeignOwnable` to `borrow_mut` let borrowed_a: ScopeGuard<Box<i32>, ...> = unsafe { Arc::<u64>::borrow_mut(a) };
but that requires `Self: Sized`. Is it too restrictive?
Regards, Boqun
> + } > + > + /// Converts a foreign-owned object back to a Rust-owned one. > + /// > + /// # Safety > + /// > + /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for > + /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet. > + /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and > + /// [`ForeignOwnable::borrow_mut`] for this object must have been dropped. > + unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self; > +} > + > /// Runs a cleanup function/closure when dropped. > /// > /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running. > -- > 2.34.1 >
| |