linux-kernel - [PATCH v2] rust: miscdevice: clarify invariant for `MiscDeviceRegistration`

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Message-Id: <20250626104520.563036-1-shankari.ak0208@gmail.com>
Date: Thu, 26 Jun 2025 16:15:20 +0530
From: Shankari Anand <shankari.ak0208@...il.com>
To: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Shankari Anand <shankari.ak0208@...il.com>
Subject: [PATCH v2] rust: miscdevice: clarify invariant for `MiscDeviceRegistration`

Reword and expand the invariant documentation for `MiscDeviceRegistration`
to clarify what it means for the inner device to be "registered".
It expands to explain:
- `inner` points to a `miscdevice` registered via `misc_register`.
- This registration stays valid for the entire lifetime of the object.
- Deregistration is guaranteed on `Drop`, via `misc_deregister`.

Reported-by: Benno Lossin <lossin@...nel.org>
Closes: https://github.com/Rust-for-Linux/linux/issues/1168
Fixes: f893691e7426 ("rust: miscdevice: add base miscdevice abstraction")
Signed-off-by: Shankari Anand <shankari.ak0208@...il.com>
---
v1 -> v2 : Added bullet points, changed the last point in the description and added intra-doc links.
---
 rust/kernel/miscdevice.rs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 288f40e79906..3fb118496958 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -45,7 +45,13 @@ pub const fn into_raw<T: MiscDevice>(self) -> bindings::miscdevice {
 ///
 /// # Invariants
 ///
-/// `inner` is a registered misc device.
+/// - `inner` contains a `struct miscdevice` that is registered using
+///   `misc_register()`.
+/// - This registration remains valid for the entire lifetime of the
+///   [`MiscDeviceRegistration`] instance.
+/// - Deregistration occurs exactly once in [`Drop`] via `misc_deregister()`.
+/// - `inner` wraps a valid, pinned `miscdevice` created using
+///   [`MiscDeviceOptions::into_raw`].
 #[repr(transparent)]
 #[pin_data(PinnedDrop)]
 pub struct MiscDeviceRegistration<T> {
 
base-commit: 0303584766b7bdb6564c7e8f13e0b59b6ef44984
-- 
2.34.1