linux-kernel - [PATCH v3 3/3] rust: miscdevice: Provide accessor to pull out miscdevice::this

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Message-ID: <20241210-miscdevice-file-param-v3-3-b2a79b666dc5@google.com>
Date: Tue, 10 Dec 2024 09:39:02 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	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 <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, Lee Jones <lee@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v3 3/3] rust: miscdevice: Provide accessor to pull out miscdevice::this_device

From: Lee Jones <lee@...nel.org>

There are situations where a pointer to a `struct device` will become
necessary (e.g. for calling into dev_*() functions).  This accessor
allows callers to pull this out from the `struct miscdevice`.

Signed-off-by: Lee Jones <lee@...nel.org>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/miscdevice.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 75a9d26c8001..20895e809607 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -10,6 +10,7 @@
 
 use crate::{
     bindings,
+    device::Device,
     error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
     fs::File,
     prelude::*,
@@ -85,6 +86,16 @@ pub fn register(opts: MiscDeviceOptions) -> impl PinInit<Self, Error> {
     pub fn as_raw(&self) -> *mut bindings::miscdevice {
         self.inner.get()
     }
+
+    /// Access the `this_device` field.
+    pub fn device(&self) -> &Device {
+        // SAFETY: This can only be called after a successful register(), which always
+        // initialises `this_device` with a valid device. Furthermore, the signature of this
+        // function tells the borrow-checker that the `&Device` reference must not outlive the
+        // `&MiscDeviceRegistration<T>` used to obtain it, so the last use of the reference must be
+        // before the underlying `struct miscdevice` is destroyed.
+        unsafe { Device::as_ref((*self.as_raw()).this_device) }
+    }
 }
 
 #[pinned_drop]

-- 
2.47.1.613.gc27f4b7a9f-goog