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

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Message-ID: <aGaN6PT-w9b2pQOr@pollux>
Date: Thu, 3 Jul 2025 16:04:24 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <lossin@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Matthew Maurer <mmaurer@...gle.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Timur Tabi <ttabi@...dia.com>, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	Dirk Behme <dirk.behme@...bosch.com>
Subject: Re: [PATCH v8 4/6] rust: debugfs: Support arbitrary owned backing
 for File

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. :)