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

Jimmy Ostler
2024-12-05T10:56:58Z

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@gmail.com>
Link: https://github.com/Rust-for-Linux/linux/issues/1131
Signed-off-by: Jimmy Ostler <jtostler1@gmail.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