linux-kernel - Re: [RFC PATCH 10/11] rust: add basic abstractions for iomem operations

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Date: Tue, 21 May 2024 00:32:02 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Danilo Krummrich <dakr@...hat.com>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com, 
	ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, a.hindborg@...sung.com, aliceryhl@...gle.com, 
	airlied@...il.com, fujita.tomonori@...il.com, lina@...hilina.net, 
	pstanner@...hat.com, ajanulgu@...hat.com, lyude@...hat.com, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org
Subject: Re: [RFC PATCH 10/11] rust: add basic abstractions for iomem operations

On Mon, May 20, 2024 at 7:27 PM Danilo Krummrich <dakr@...hat.com> wrote:
>
> through its Drop() implementation.

Nit: `Drop`, `Deref` and so on are traits -- what do the `()` mean
here? I guess you may be referring to their method, but those are
lowercase.

> +/// IO-mapped memory, starting at the base pointer @ioptr and spanning @malxen bytes.

Please use Markdown code spans instead (and intra-doc links where
possible) -- we don't use the `@` notation. There is a typo on the
variable name too.

> +pub struct IoMem {
> +    pub ioptr: usize,

This field is public, which raises some questions...

> +    pub fn readb(&self, offset: usize) -> Result<u8> {
> +        let ioptr: usize = self.get_io_addr(offset, 1)?;
> +
> +        Ok(unsafe { bindings::readb(ioptr as _) })
> +    }

These methods are unsound, since `ioptr` may end up being anything
here, given `self.ioptr` it is controlled by the caller. One could
also trigger an overflow in `get_io_addr`.

Wedson wrote a similar abstraction in the past
(`rust/kernel/io_mem.rs` in the old `rust` branch), with a
compile-time `SIZE` -- it is probably worth taking a look.

Also, there are missing `// SAFETY:` comments here. Documentation and
examples would also be nice to have.

Thanks!

Cheers,
Miguel