Re: [PATCH WIP 1/2] rust: debugfs: Add interface to build debugfs off pinned objects

[Danilo Krummrich <dakr@kernel.org>]

On Sat, May 03, 2025 at 12:43:59AM +0000, Matthew Maurer wrote:
> +/// A DebugFS directory combined with a backing store for data to implement it.
> +#[pin_data]
> +pub struct Values<T> {
> +    dir: Dir<'static, false>,
> +    // The order here is load-bearing - `dir` must be dropped before `backing`, as files under
> +    // `dir` may point into `backing`.
> +    #[pin]
> +    backing: T,
> +    // Since the files present under our directory may point into `backing`, we are `!Unpin`.
> +    #[pin]
> +    _pin: PhantomPinned,
> +}

This only ever allows attaching data to the root directory, correct? What if I
want to remove (or replace) a file or a subdir? Then I'd be left with the data
for this specific file (or subdir) until the root is finally removed.

It would also require Option<V> (where V is the type of a field in T), if I
don't have an instance of V yet, when the root directory is created.

I think we should store the data per file, rather than per root directory.