[PATCH] rust: bitmap: document panics in `next_bit` and `next_zero_bit`

[PATCH] rust: bitmap: document panics in `next_bit` and `next_zero_bit`

[Georgios Androutsopoulos]

`next_bit()` and `next_zero_bit()` use `bitmap_assert!()` to check
that `start` is less than `self.len()`, which panics when
`CONFIG_RUST_BITMAP_HARDENED` is enabled. However, neither function
has a `# Panics` section, and both document that `None` is returned
for exactly the input that triggers the panic.

Add the missing `# Panics` sections and condition the `None` case on
`CONFIG_RUST_BITMAP_HARDENED` being disabled, matching the style used
by `set_bit()`, `clear_bit()` and their atomic versions in the same
file. Also add the missing blank doc comment line before `Returns` in
`next_zero_bit()`.

Link: https://github.com/Rust-for-Linux/linux/issues/1252

Signed-off-by: Georgios Androutsopoulos <georgeandrout13@gmail.com>
---
 rust/kernel/bitmap.rs | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
index b27e0ec80..b33f7ce5c 100644
--- a/rust/kernel/bitmap.rs
+++ b/rust/kernel/bitmap.rs
@@ -459,7 +459,13 @@ pub fn last_bit(&self) -> Option<usize> {
 
     /// Finds next set bit, starting from `start`.
     ///
-    /// Returns `None` if `start` is greater or equal to `self.nbits`.
+    /// If `CONFIG_RUST_BITMAP_HARDENED` is not enabled and `start` is greater
+    /// than or equal to `self.len()`, returns `None`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `CONFIG_RUST_BITMAP_HARDENED` is enabled and `start` is
+    /// greater than or equal to `self.len()`.
     #[inline]
     pub fn next_bit(&self, start: usize) -> Option<usize> {
         bitmap_assert!(
@@ -479,7 +485,14 @@ pub fn next_bit(&self, start: usize) -> Option<usize> {
     }
 
     /// Finds next zero bit, starting from `start`.
-    /// Returns `None` if `start` is greater than or equal to `self.len()`.
+    ///
+    /// If `CONFIG_RUST_BITMAP_HARDENED` is not enabled and `start` is greater
+    /// than or equal to `self.len()`, returns `None`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `CONFIG_RUST_BITMAP_HARDENED` is enabled and `start` is
+    /// greater than or equal to `self.len()`.
     #[inline]
     pub fn next_zero_bit(&self, start: usize) -> Option<usize> {
         bitmap_assert!(

base-commit: 73e3f0710014fe6d4ed98cfc02292f6121db7558
-- 
2.47.3

Re: [PATCH] rust: bitmap: document panics in `next_bit` and `next_zero_bit`

[Alice Ryhl]

On Thu, Aug 27, 2026 at 11:07:19AM -0400, Georgios Androutsopoulos wrote:
> `next_bit()` and `next_zero_bit()` use `bitmap_assert!()` to check
> that `start` is less than `self.len()`, which panics when
> `CONFIG_RUST_BITMAP_HARDENED` is enabled. However, neither function
> has a `# Panics` section, and both document that `None` is returned
> for exactly the input that triggers the panic.
> 
> Add the missing `# Panics` sections and condition the `None` case on
> `CONFIG_RUST_BITMAP_HARDENED` being disabled, matching the style used
> by `set_bit()`, `clear_bit()` and their atomic versions in the same
> file. Also add the missing blank doc comment line before `Returns` in
> `next_zero_bit()`.
> 
> Link: https://github.com/Rust-for-Linux/linux/issues/1252
> 
> Signed-off-by: Georgios Androutsopoulos <georgeandrout13@gmail.com>

There's an unncessary empty newline between Link: and Signed-off-by:

>  rust/kernel/bitmap.rs | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
> index b27e0ec80..b33f7ce5c 100644
> --- a/rust/kernel/bitmap.rs
> +++ b/rust/kernel/bitmap.rs
> @@ -459,7 +459,13 @@ pub fn last_bit(&self) -> Option<usize> {
>  
>      /// Finds next set bit, starting from `start`.
>      ///
> -    /// Returns `None` if `start` is greater or equal to `self.nbits`.
> +    /// If `CONFIG_RUST_BITMAP_HARDENED` is not enabled and `start` is greater
> +    /// than or equal to `self.len()`, returns `None`.
> +    ///
> +    /// # Panics
> +    ///
> +    /// Panics if `CONFIG_RUST_BITMAP_HARDENED` is enabled and `start` is
> +    /// greater than or equal to `self.len()`.

This wording is a bit repetetive. I think we can simplify to:

/// Finds next set bit, starting from `start`.
///
/// Returns `None` if no bits are set on or after the given index. The
/// index `start` must be in bounds.
///
/// # Panics
///
/// Panics if `CONFIG_RUST_BITMAP_HARDENED` is enabled and `start` is
/// out of bounds.

Alice