linux-kernel - Re: [PATCH v3 3/5] samples: rust: Provide example using the new Rust MiscDevice abstraction

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Message-Id: <be74daeb-68af-4e6b-8091-7f9684fe424e@app.fastmail.com>
Date: Fri, 06 Dec 2024 07:52:46 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Lee Jones" <lee@...nel.org>
Cc: linux-kernel@...r.kernel.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>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 3/5] samples: rust: Provide example using the new Rust
 MiscDevice abstraction

On Fri, Dec 6, 2024, at 07:49, Greg KH wrote:
> On Thu, Dec 05, 2024 at 04:25:20PM +0000, Lee Jones wrote:
>> +
>> +#[vtable]
>> +impl MiscDevice for RustMiscDevice {
>> +    type Ptr = KBox<Self>;
>> +
>> +    fn open() -> Result<KBox<Self>> {
>> +        pr_info!("Opening Rust Misc Device Sample\n");
>> +
>> +        Ok(KBox::new(RustMiscDevice, GFP_KERNEL)?)
>> +    }
>> +
>> +    fn ioctl(
>> +        _device: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
>> +        cmd: u32,
>> +        _arg: usize,
>> +    ) -> Result<isize> {
>> +        pr_info!("IOCTLing Rust Misc Device Sample\n");
>> +
>> +        match cmd {
>> +            RUST_MISC_DEV_HELLO => pr_info!("Hello from the Rust Misc Device\n"),
>> +            _ => {
>> +                pr_err!("IOCTL not recognised: {}\n", cmd);
>> +                return Err(ENOIOCTLCMD);
>
> To quote errno.h:
> 	These should never be seen by user programs
>
> The correct value here is ENOTTY.
>
> Yeah, fun stuff.  Not intuitive at all, sorry.

That should get handled by vfs_ioctl() converting the
ENOIOCTLCMD to ENOTTY.

       Arnd