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Date: Fri, 6 Dec 2024 08:03:34 +0100
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Lee Jones <lee@kernel.org>, linux-kernel@vger.kernel.org,
	Miguel Ojeda <ojeda@kernel.org>,
	Alex Gaynor <alex.gaynor@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
	Benno Lossin <benno.lossin@proton.me>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Alice Ryhl <aliceryhl@google.com>, Trevor Gross <tmgross@umich.edu>,
	rust-for-linux@vger.kernel.org
Subject: Re: [PATCH v3 3/5] samples: rust: Provide example using the new Rust
 MiscDevice abstraction
Message-ID: <2024120621-unlisted-unbalance-3220@gregkh>
References: <20241205162531.1883859-1-lee@kernel.org>
 <20241205162531.1883859-4-lee@kernel.org>
 <2024120642-trend-omnivore-69d3@gregkh>
 <be74daeb-68af-4e6b-8091-7f9684fe424e@app.fastmail.com>
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In-Reply-To: <be74daeb-68af-4e6b-8091-7f9684fe424e@app.fastmail.com>

On Fri, Dec 06, 2024 at 07:52:46AM +0100, Arnd Bergmann wrote:
> 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.

Ah, I always miss that, for some reason I thought that didn't happen
there, but happened in subsystems that did ENOIOCTLCMD for their
sub-ioctl handlers.  And yet it's always been that way, nevermind...

Anyway, I always recommend just using ENOTTY to be "safe", the usual way
people get this wrong is using EINVAL.

thanks,

greg k-h