Re: [PATCH v8 4/6] rust: debugfs: Support arbitrary owned backing for File

["Benno Lossin" <lossin@kernel.org>]

On Thu Jul 3, 2025 at 2:29 PM CEST, Danilo Krummrich wrote:
> So, what I'm trying to say is, I think it's a good thing if fields that are
> protected by the same lock can't be exposed through separate files, because it
> means that the fields only make sense in the context of each other.

I think that even the pin-init API can have multiple files for different
elements of the locked structure, you just need to nest `File`:

    #[pin_data]
    struct Process {
        task: ARef<Task>,
        #[pin]
        inner: File<File<SpinLock<ProcessInner>>>,
    }
    
    pub(crate) struct ProcessInner {
        threads: RBTree<i32, Arc<Thread>>,
        max_threads: u32,
    }

Now you can do:

    pin_init!(Process {
        inner <- dir.create_file(
            "threads",
            dir.create_file("max_threads", new_spinlock!(...)),
        ),
        // ...
    })

But I'd say this will at least raise eyebrows for the reviewers, which
is good, since it catches the footgun.

---
Cheers,
Benno