linux-kernel - Re: [PATCH v2 1/2] rust: types: add Opaque::try_ffi

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Message-ID: <CALNs47tbt46VAcT5rm0Y6QBP6kc4ocBFDPOZugthPmNdaHrwPQ@mail.gmail.com>
Date: Thu, 24 Oct 2024 23:10:10 -0500
From: Trevor Gross <tmgross@...ch.edu>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Miguel Ojeda <ojeda@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] rust: types: add Opaque::try_ffi_init

On Tue, Oct 1, 2024 at 3:23 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> This will be used by the miscdevice abstractions, as the C function
> `misc_register` is fallible.
>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>  rust/kernel/types.rs | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 9e7ca066355c..070d03152937 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -299,6 +299,22 @@ pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
>          }
>      }
>
> +    /// Creates a fallible pin-initializer from the given initializer closure.
> +    ///
> +    /// The returned initializer calls the given closure with the pointer to the inner `T` of this
> +    /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it.
> +    ///
> +    /// This function is safe, because the `T` inside of an `Opaque` is allowed to be
> +    /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs
> +    /// to verify at that point that the inner value is valid.
> +    pub fn try_ffi_init<E>(
> +        init_func: impl FnOnce(*mut T) -> Result<(), E>,
> +    ) -> impl PinInit<Self, E> {
> +        // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully
> +        // initialize the `T`.
> +        unsafe { init::pin_init_from_closure::<_, E>(move |slot| init_func(Self::raw_get(slot))) }
> +    }

[1] adjusts `ffi_init` to use `try_ffi_init`. Maybe this should do the same?

[1]: https://lore.kernel.org/rust-for-linux/20241022213221.2383-2-dakr@kernel.org/