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

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Message-ID: <CAH5fLgj=+aXo3sj9wKJudHYtL5pBHB8AzGS5njWEDzD0wydrOw@mail.gmail.com>
Date: Fri, 25 Oct 2024 09:57:59 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Trevor Gross <tmgross@...ch.edu>
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 Fri, Oct 25, 2024 at 6:10 AM Trevor Gross <tmgross@...ch.edu> wrote:
>
> 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/

Ah, I wasn't able to find previous patches for this, but I guess there was one.

This patch has already landed in char-misc-next, so this can be a
follow-up if you want to change it.

Alice