linux-kernel - Re: [PATCH v4 1/3] rust: io: add resource abstraction

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Message-ID: <CAH5fLgjC3mOp688vGgfhv5Bq0TzbaXuE1DMTXk3Ck7UqxJi+Pg@mail.gmail.com>
Date: Thu, 9 Jan 2025 14:46:59 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: alex.gaynor@...il.com, boqun.feng@...il.com, gary@...yguo.net, 
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, a.hindborg@...nel.org, 
	tmgross@...ch.edu, gregkh@...uxfoundation.org, rafael@...nel.org, 
	dakr@...nel.org, boris.brezillon@...labora.com, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] rust: io: add resource abstraction

On Thu, Jan 9, 2025 at 2:32 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
>
> In preparation for ioremap support, add a Rust abstraction for struct
> resource.
>
> A future commit will introduce the Rust API to ioremap a resource from a
> platform device. The current abstraction, therefore, adds only the
> minimum API needed to get that done.
>
> Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
> ---
>  rust/bindings/bindings_helper.h |  1 +
>  rust/helpers/io.c               |  7 +++++
>  rust/kernel/io.rs               |  2 ++
>  rust/kernel/io/resource.rs      | 49 +++++++++++++++++++++++++++++++++
>  4 files changed, 59 insertions(+)
>  create mode 100644 rust/kernel/io/resource.rs
>
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index e9fdceb568b8..f9c2eedb5b9b 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -16,6 +16,7 @@
>  #include <linux/file.h>
>  #include <linux/firmware.h>
>  #include <linux/fs.h>
> +#include <linux/ioport.h>
>  #include <linux/jiffies.h>
>  #include <linux/jump_label.h>
>  #include <linux/mdio.h>
> diff --git a/rust/helpers/io.c b/rust/helpers/io.c
> index 4c2401ccd720..3cb47bd01942 100644
> --- a/rust/helpers/io.c
> +++ b/rust/helpers/io.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>
>  #include <linux/io.h>
> +#include <linux/ioport.h>
>
>  void __iomem *rust_helper_ioremap(phys_addr_t offset, size_t size)
>  {
> @@ -99,3 +100,9 @@ void rust_helper_writeq_relaxed(u64 value, volatile void __iomem *addr)
>         writeq_relaxed(value, addr);
>  }
>  #endif
> +
> +resource_size_t rust_helper_resource_size(struct resource *res)
> +{
> +       return resource_size(res);
> +}
> +
> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> index d4a73e52e3ee..566d8b177e01 100644
> --- a/rust/kernel/io.rs
> +++ b/rust/kernel/io.rs
> @@ -7,6 +7,8 @@
>  use crate::error::{code::EINVAL, Result};
>  use crate::{bindings, build_assert};
>
> +pub mod resource;
> +
>  /// Raw representation of an MMIO region.
>  ///
>  /// By itself, the existence of an instance of this structure does not provide any guarantees that
> diff --git a/rust/kernel/io/resource.rs b/rust/kernel/io/resource.rs
> new file mode 100644
> index 000000000000..84876af1699c
> --- /dev/null
> +++ b/rust/kernel/io/resource.rs
> @@ -0,0 +1,49 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Abstraction for system resources.
> +//!
> +//! C header: [`include/linux/ioport.h`](../../../../include/linux/ioport.h)

Please use srctree instead of ../../../..

> +use crate::str::CStr;
> +use crate::types::Opaque;
> +
> +/// A resource abstraction.
> +#[repr(transparent)]
> +pub struct Resource(Opaque<bindings::resource>);
> +
> +impl Resource {
> +    /// Creates a reference to a [`Resource`] from a valid pointer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// The caller must ensure that for the duration of 'a, the pointer will
> +    /// point at a valid `bindings::resource`
> +    ///
> +    /// The caller must also ensure that the `Resource` is only accessed via the
> +    /// returned reference for the duration of 'a.
> +    pub(crate) unsafe fn from_ptr<'a>(ptr: *mut bindings::resource) -> &'a Self {
> +        // SAFETY: Self is a transparent wrapper around `Opaque<bindings::resource>`.
> +        unsafe { &mut *ptr.cast() }

Please remove the `mut` here.

> +    }
> +
> +    /// Returns the size of the resource.
> +    pub fn size(&self) -> bindings::resource_size_t {
> +        let inner = self.0.get();
> +        // SAFETY: safe as per the invariants of `Resource`

If you're going to refer to the invariants of Reserve, then it should
have an "# Invariants" section.

> +        unsafe { bindings::resource_size(inner) }
> +    }
> +
> +    /// Returns the start address of the resource.
> +    pub fn start(&self) -> u64 {
> +        let inner = self.0.get();
> +        // SAFETY: safe as per the invariants of `Resource`
> +        unsafe { *inner }.start
> +    }
> +
> +    /// Returns the name of the resource.
> +    pub fn name(&self) -> &CStr {
> +        let inner = self.0.get();
> +        // SAFETY: safe as per the invariants of `Resource`
> +        unsafe { CStr::from_char_ptr((*inner).name) }
> +    }
> +}
> --
> 2.47.1
>