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

[Danilo Krummrich <dakr@kernel.org>]

On Thu, Jul 03, 2025 at 03:34:23PM +0200, Benno Lossin wrote:
> 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.

Heh! I didn't even think of this trick. I agree, this should at least raise some
eyebrows. :)