linux-kernel - Re: [PATCH v2 2/2] rust: miscdevice: add base miscdevice abstraction

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Message-ID: <CAH5fLgjCA77nAYqZLus7TWbW7mOKC1MKn+jJL-_tpQSR-h-r8w@mail.gmail.com>
Date: Tue, 1 Oct 2024 13:28:53 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: 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>
Cc: 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>, 
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rust: miscdevice: add base miscdevice abstraction

On Tue, Oct 1, 2024 at 10:22 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> +impl<T: MiscDevice> MiscDeviceRegistration<T> {
> +    /// Register a misc device.
> +    pub fn register(opts: MiscDeviceOptions) -> impl PinInit<Self, Error> {
> +        try_pin_init!(Self {
> +            inner <- Opaque::try_ffi_init(move |slot: *mut bindings::miscdevice| {
> +                // SAFETY: The initializer can write to the provided `slot`.
> +                unsafe { slot.write(opts.into_raw::<T>()) };
> +
> +                // SAFETY: We just wrote the misc device options to the slot. The miscdevice will
> +                // get unregistered before `slot` is deallocated because the memory is pinned and
> +                // the destructor of this type deallocates the memory.
> +                // INVARIANT: If this returns `Ok(())`, then the `slot` will contain a registered
> +                // misc device.
> +                to_result(unsafe { bindings::misc_register(slot) })
> +            }),
> +            _t: PhantomData,
> +        })
> +    }

Note that right now this can only be used in the module init function
if the registration is stored in a pinned box. We need the in-place
initialization change to fix that.

Does anyone want to revive the in-place initialization patch?

Link: https://lore.kernel.org/rust-for-linux/20240328195457.225001-1-wedsonaf@gmail.com/

Alice