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

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Message-ID: <20241001-b4-miscdevice-v2-1-330d760041fa@google.com>
Date: Tue, 01 Oct 2024 08:22:21 +0000
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, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v2 1/2] rust: types: add Opaque::try_ffi_init

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))) }
+    }
+
     /// Returns a raw pointer to the opaque data.
     pub const fn get(&self) -> *mut T {
         UnsafeCell::get(&self.value).cast::<T>()

-- 
2.46.1.824.gd892dcdcdd-goog