Re: [PATCH v2 1/4] rust: debugfs: Bind DebugFS directory creation

[Danilo Krummrich <dakr@kernel.org>]

On Wed, Apr 30, 2025 at 11:31:56PM +0000, Matthew Maurer wrote:
> 
> +    /// Create a DebugFS subdirectory.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// # use kernel::c_str;
> +    /// # use kernel::debugfs::Dir;
> +    /// {
> +    ///    let parent = Dir::new(c_str!("parent"));
> +    ///    // parent exists in DebugFS here.
> +    ///    let child = parent.subdir(c_str!("child"));
> +    ///    // parent/child exists in DebugFS here.
> +    /// }
> +    /// // Neither exist here.
> +    /// ```
> +    pub fn subdir(&self, name: &CStr) -> Self {
> +        Self::create(name, Some(self))
> +    }

I think this should return a new type (SubDir), which is a transparent wrapper
of Dir and dereferences to Dir.

Subsequently, we can remove Dir::keep() implement SubDir::keep() instead. This
ensures that we can never call keep() on the root directory, which would always
be a bug.

As an alternative to the Deref impl, you can also implement
`From<SubDir> for Dir`, such that a SubDir can either be "kept" or converted to
a Dir. Probably, that's even better.