Re: [PATCH 2/2] rust: page: add method to copy data between safe pages

[Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>]

On Sun, Feb 15, 2026 at 9:04 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> +    /// Copies data from this page to another page at the specified offset.
> +    ///
> +    /// # Arguments
> +    ///
> +    /// - `dst` - The destination page to copy data to.
> +    /// - `offset` - The byte offset within both pages where copying starts.
> +    /// - `len` - The number of bytes to copy.

We generally try to avoid this kind of argument-by-argument docs
unless they are really needed.

For instance, would this suffice?

  /// Copies `len` bytes from this page to another one at the
specified byte offset.
  ///
  /// Copying starts within both pages at the same offset.

> +    /// ```
> +    /// # use kernel::page::SafePage;
> +    /// # use kernel::alloc::flags::GFP_KERNEL;
> +    /// let mut src_page = SafePage::alloc_page(GFP_KERNEL)?;
> +    /// let mut dst_page = SafePage::alloc_page(GFP_KERNEL)?;
> +    /// src_page.copy_to_page(dst_page.get_pin_mut(), 0, 1024)?;
> +    /// # Ok::<(), kernel::error::Error>(())
> +    /// ```

Could we show some error cases?

In addition, why could the test fail here? i.e. if you use `?` in the
"main line", then it means this could fail for reasons outside the
test. If it cannot, please assert it instead.

Also, couldn't you assert that some bytes were copied as expected?
Could you show an error case with e.g. an out of bounds case?

> +            // - By type invariant and existence of shared reference, there are no other writes to
> +            //   `src` during this call.

If you use the type invariant here that you promise not to break
above, isn't it circular logic? Why someone couldn't have another
`&self` and call this?

Cheers,
Miguel