From: Boqun Feng <boqun.feng@gmail.com>
To: Wedson Almeida Filho <wedsonaf@gmail.com>
Cc: rust-for-linux@vger.kernel.org, "Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/5] rust: types: introduce `ForeignOwnable`
Date: Fri, 20 Jan 2023 11:59:29 -0800 [thread overview]
Message-ID: <Y8ryoTYIKpYtuqow@boqun-archlinux> (raw)
In-Reply-To: <20230119174036.64046-2-wedsonaf@gmail.com>
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
>
next prev parent reply other threads:[~2023-01-20 20:00 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-19 17:40 [PATCH 1/5] rust: types: introduce `ScopeGuard` Wedson Almeida Filho
2023-01-19 17:40 ` [PATCH 2/5] rust: types: introduce `ForeignOwnable` Wedson Almeida Filho
2023-01-20 19:59 ` Boqun Feng [this message]
2023-01-22 6:34 ` Wedson Almeida Filho
2023-01-27 13:55 ` Gary Guo
2023-01-30 5:59 ` Wedson Almeida Filho
2023-01-28 10:42 ` Vincenzo Palazzo
2023-01-28 14:53 ` Martin Rodriguez Reboredo
2023-01-28 17:05 ` Boqun Feng
2023-01-28 20:46 ` Martin Rodriguez Reboredo
2023-01-28 22:07 ` Boqun Feng
2023-01-29 3:52 ` Martin Rodriguez Reboredo
2023-01-19 17:40 ` [PATCH 3/5] rust: types: implement `ForeignOwnable` for `Box<T>` Wedson Almeida Filho
2023-01-27 13:56 ` Gary Guo
2023-01-28 10:50 ` Vincenzo Palazzo
2023-01-30 5:33 ` Alice Ferrazzi
2023-01-19 17:40 ` [PATCH 4/5] rust: types: implement `ForeignOwnable` for the unit type Wedson Almeida Filho
2023-01-27 14:03 ` Gary Guo
2023-01-27 14:11 ` Miguel Ojeda
2023-01-28 11:13 ` Vincenzo Palazzo
2023-01-30 17:21 ` Miguel Ojeda
2023-01-30 5:55 ` Wedson Almeida Filho
2023-01-28 11:14 ` Vincenzo Palazzo
2023-01-19 17:40 ` [PATCH 5/5] rust: types: implement `ForeignOwnable` for `Arc<T>` Wedson Almeida Filho
2023-01-27 14:04 ` Gary Guo
2023-01-28 11:15 ` Vincenzo Palazzo
2023-01-30 5:35 ` Alice Ferrazzi
2023-01-20 6:23 ` [PATCH 1/5] rust: types: introduce `ScopeGuard` Boqun Feng
2023-01-22 6:31 ` Wedson Almeida Filho
2023-01-28 10:38 ` Vincenzo Palazzo
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