linux-kernel - [PATCH v2] rust: alloc: Add doctest for `ArrayLayout`

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Message-ID: <20241205105627.992587-1-jtostler1@gmail.com>
Date: Thu,  5 Dec 2024 02:56:27 -0800
From: Jimmy Ostler <jtostler1@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Filipe Xavier <felipe_life@...e.com>,
	Valentin Obst <kernel@...entinobst.de>
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jimmy Ostler <jtostler1@...il.com>
Subject: [PATCH v2] rust: alloc: Add doctest for `ArrayLayout`

Add a rustdoc example and Kunit test to the `ArrayLayout` struct's
`ArrayLayout::new()` function.

Add an implementation of `From<LayoutError> for Error` for the
`kernel::alloc::LayoutError`. This is necessary for the new test to
compile.

Change the `From` implementation on `core::alloc::LayoutError` to avoid
collisions with `kernel::alloc::LayoutError`, and modify imports to
explicitly import `kernel::alloc::LayoutError` instead.

Suggested-by: Boqun Feng <boqun.feng@...il.com>
Link: https://github.com/Rust-for-Linux/linux/issues/1131
Signed-off-by: Jimmy Ostler <jtostler1@...il.com>
---
v1: https://lore.kernel.org/lkml/20241203051843.291729-1-jtostler1@gmail.com/T/#u
v1 -> v2 changes:
- Add third assert where length is smaller but still overflows
- Remove rustdoc markdown codeblock languge signifier
- Change tests to return results using `?` instead of panic
- Remove `#[derive(Debug)]` for `LayoutError`
- Add `From<LayoutError> for Error` implementation
---
 rust/kernel/alloc/layout.rs | 19 +++++++++++++++++++
 rust/kernel/error.rs        | 13 ++++++++++---
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/alloc/layout.rs b/rust/kernel/alloc/layout.rs
index 4b3cd7fdc816..0e053dcc7941 100644
--- a/rust/kernel/alloc/layout.rs
+++ b/rust/kernel/alloc/layout.rs
@@ -43,6 +43,25 @@ pub const fn empty() -> Self {
     /// # Errors
     ///
     /// When `len * size_of::<T>()` overflows or when `len * size_of::<T>() > isize::MAX`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::alloc::layout::{ArrayLayout, LayoutError};
+    /// let layout = ArrayLayout::<i32>::new(15)?;
+    /// assert_eq!(layout.len(), 15);
+    ///
+    /// // Errors because `len * size_of::<T>()` overflows
+    /// let layout = ArrayLayout::<i32>::new(isize::MAX as usize);
+    /// assert!(layout.is_err());
+    ///
+    /// // Errors because `len * size_of::<i32>() > isize::MAX`,
+    /// // even though `len < isize::MAX`
+    /// let layout = ArrayLayout::<i32>::new(isize::MAX as usize / 2);
+    /// assert!(layout.is_err());
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
     pub const fn new(len: usize) -> Result<Self, LayoutError> {
         match len.checked_mul(core::mem::size_of::<T>()) {
             Some(size) if size <= ISIZE_MAX => {
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 52c502432447..ac8526140d7a 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -4,9 +4,10 @@
 //!
 //! C header: [`include/uapi/asm-generic/errno-base.h`](srctree/include/uapi/asm-generic/errno-base.h)
 
-use crate::{alloc::AllocError, str::CStr};
-
-use core::alloc::LayoutError;
+use crate::{
+    alloc::{layout::LayoutError, AllocError},
+    str::CStr,
+};
 
 use core::fmt;
 use core::num::NonZeroI32;
@@ -223,6 +224,12 @@ fn from(_: LayoutError) -> Error {
     }
 }
 
+impl From<core::alloc::LayoutError> for Error {
+    fn from(_: core::alloc::LayoutError) -> Error {
+        code::ENOMEM
+    }
+}
+
 impl From<core::fmt::Error> for Error {
     fn from(_: core::fmt::Error) -> Error {
         code::EINVAL

base-commit: 1dc707e647bc919834eff9636c8d00b78c782545
-- 
2.47.1