linux-kernel - [PATCH] rust: device: change the from

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Message-ID: <20240930194637.98260-1-trintaeoitogc@gmail.com>
Date: Mon, 30 Sep 2024 16:46:34 -0300
From: Guilherme Giacomo Simoes <trintaeoitogc@...il.com>
To: gregkh@...uxfoundation.org,
	rafael@...nel.org,
	ojeda@...nel.org,
	alex.gaynor@...il.com,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me,
	aliceryhl@...gle.com,
	mcgrof@...nel.org,
	russ.weight@...ux.dev,
	dakr@...hat.com,
	a.hindborg@...nel.org
Cc: Guilherme Giacomo Simoes <trintaeoitogc@...il.com>,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] rust: device: change the from_raw() function

The function Device::from_raw() increments a refcount by a call to
bindings::get_device(ptr). This can be confused because usually
from_raw() functions don't increment a refcount.
Hence, rename Device::from_raw() to avoid confuion with other "from_raw"
semantics.

The new name of function should be "get_device" to be consistent with
the function get_device() already exist in .c files.

This function body also changed, because the `into()` will convert the
`&'a Device` into `ARef<Device>` and also call `inc_ref` from the
`AlwaysRefCounted` trait implemented for Device.

Signed-off-by: Guilherme Giacomo Simoes <trintaeoitogc@...il.com>
---
 rust/kernel/device.rs   | 15 +++------------
 rust/kernel/firmware.rs |  2 +-
 2 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 851018eef885..c8199ee079ef 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -51,18 +51,9 @@ impl Device {
     ///
     /// It must also be ensured that `bindings::device::release` can be called from any thread.
     /// While not officially documented, this should be the case for any `struct device`.
-    pub unsafe fn from_raw(ptr: *mut bindings::device) -> ARef<Self> {
-        // SAFETY: By the safety requirements, ptr is valid.
-        // Initially increase the reference count by one to compensate for the final decrement once
-        // this newly created `ARef<Device>` instance is dropped.
-        unsafe { bindings::get_device(ptr) };
-
-        // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::device`.
-        let ptr = ptr.cast::<Self>();
-
-        // SAFETY: `ptr` is valid by the safety requirements of this function. By the above call to
-        // `bindings::get_device` we also own a reference to the underlying `struct device`.
-        unsafe { ARef::from_raw(ptr::NonNull::new_unchecked(ptr)) }
+    pub unsafe fn get_device(ptr: *mut bindings::device) -> ARef<Self> {
+        // SAFETY: By the safety requirements ptr is valid
+        unsafe { Self::as_ref(ptr) }.into()
     }
 
     /// Obtain the raw `struct device *`.
diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index dee5b4b18aec..13a374a5cdb7 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -44,7 +44,7 @@ fn request_nowarn() -> Self {
 ///
 /// # fn no_run() -> Result<(), Error> {
 /// # // SAFETY: *NOT* safe, just for the example to get an `ARef<Device>` instance
-/// # let dev = unsafe { Device::from_raw(core::ptr::null_mut()) };
+/// # let dev = unsafe { Device::get_device(core::ptr::null_mut()) };
 ///
 /// let fw = Firmware::request(c_str!("path/to/firmware.bin"), &dev)?;
 /// let blob = fw.data();
-- 

The motivation from this change was will discussion in:
https://rust-for-linux.zulipchat.com/#narrow/stream/291566-Library/topic/Inconsistency.20of.20.60from_raw.60.2E

I would like to thanks for Greg <gregkh@...uxfoundation.org>, Danilo
<dakr@...nel.org> and Alice <aliceryhl@...gle.com> for help me with this
patch.

2.46.2