Messages in this thread |  | | From | Wedson Almeida Filho <> | Date | Sun, 22 Jan 2023 03:34:40 -0300 | Subject | Re: [PATCH 2/5] rust: types: introduce `ForeignOwnable` |
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On Fri, 20 Jan 2023 at 16:59, Boqun Feng <boqun.feng@gmail.com> wrote: > > 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(); > }) > }
Oh, eliminate the generic type `T` and just use `Self`. Yes, I think that's a good simplification.
> > 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?
It isn't. Since we want the raw pointer to fit in a single pointer (from C's perspective), we already require `Self: Sized`.
I'll make this change in v2.
> > 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 > >
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