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

This patch depends on the first patch in this series in order for the
kunit test to compile.

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>
---
 rust/kernel/alloc/layout.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

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 => {
-- 
2.47.1

On Tue, Dec 17, 2024 at 04:23:12PM -0800, Jimmy Ostler wrote:
> Add a rustdoc example and Kunit test to the `ArrayLayout` struct's
> `ArrayLayout::new()` function.
> 
> This patch depends on the first patch in this series in order for the
> kunit test to compile.
> 
> 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>


Reviewed-by: Danilo Krummrich <dakr@kernel.org>

> ---
>  rust/kernel/alloc/layout.rs | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> 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 => {
> -- 
> 2.47.1
>