linux-kernel - Re: [PATCH v4 2/4] samples: rust: Provide example using the new Rust MiscDevice abstraction

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Message-ID: <CAH5fLgjauL-1QbnkVVK34COD_Ch_rcdpUEMKBsC9HB-TKWNscA@mail.gmail.com>
Date: Fri, 6 Dec 2024 11:09:02 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 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>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v4 2/4] samples: rust: Provide example using the new Rust
 MiscDevice abstraction

On Fri, Dec 6, 2024 at 11:05 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, Dec 6, 2024, at 10:05, Lee Jones wrote:
> > This sample driver demonstrates the following basic operations:
> >
> > * Register a Misc Device
> > * Create /dev/rust-misc-device
> > * Provide open call-back for the aforementioned character device
> > * Operate on the character device via a simple ioctl()
> > * Provide close call-back for the character device
> >
> > Signed-off-by: Lee Jones <lee@...nel.org>
>
> Could you include a compat_ioctl() callback in the example?
> I think it would be good to include it as a reminder for
> authors of actual drivers that every driver implementing
> ioctl should also implement compat_ioctl. In C drivers, this
> can usually be done by pointing .compat_ioctl() to the
> generic compat_ptr_ioctl() function, which assumes that 'arg'
> is a pointer disguised as an 'unsigned long'.

The current Rust logic for building the fops table will use
compat_ptr_ioctl() automatically if you specify ioctl() but don't
specify compat_ioctl(), so this already uses compat_ptr_ioctl(). But
maybe that's not what we want?

Alice