linux-kernel - Re: [PATCH v2 2/5] rust: Add bindings for reading device properties

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Message-ID: <d179848e-63e1-4921-891e-455834f3733e@de.bosch.com>
Date: Wed, 23 Apr 2025 14:29:11 +0200
From: Dirk Behme <dirk.behme@...bosch.com>
To: Remo Senekowitsch <remo@...nzli.dev>, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>, 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>, Danilo Krummrich <dakr@...nel.org>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
	<rafael@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] rust: Add bindings for reading device properties

Hi Remo,

On 14/04/2025 17:26, Remo Senekowitsch wrote:
> The device property API is a firmware agnostic API for reading
> properties from firmware (DT/ACPI) devices nodes and swnodes.
> 
> While the C API takes a pointer to a caller allocated variable/buffer,
> the rust API is designed to return a value and can be used in struct
> initialization. Rust generics are also utilized to support different
> types of properties where appropriate.
> 
> The PropertyGuard is a way to force users to specify whether a property
> is supposed to be required or not. This allows us to move error
> logging of missing required properties into core, preventing a lot of
> boilerplate in drivers.
> 
> Co-developed-by: Rob Herring (Arm) <robh@...nel.org>
> Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> Signed-off-by: Remo Senekowitsch <remo@...nzli.dev>
> ---
>  rust/kernel/property.rs | 385 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 383 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/property.rs b/rust/kernel/property.rs
> index f6e6c980d..0d4ea3168 100644
> --- a/rust/kernel/property.rs
> +++ b/rust/kernel/property.rs
...
> +    /// helper used to display name or path of a fwnode
> +    ///
> +    /// # Safety
> +    ///
> +    /// Callers must provide a valid format string for a fwnode.
> +    unsafe fn fmt(&self, f: &mut core::fmt::Formatter<'_>, fmt_str: &CStr) -> core::fmt::Result {
> +        let mut buf = [0; 256];
> +        // SAFETY: `buf` is valid and `buf.len()` is its length. `self.as_raw()` is
> +        // valid because `self` is valid.
> +        let written = unsafe {
> +            bindings::scnprintf(buf.as_mut_ptr(), buf.len(), fmt_str.as_ptr(), self.as_raw())
> +        };
> +        // SAFETY: `written` is smaller or equal to `buf.len()`.
> +        let b: &[u8] = unsafe { core::slice::from_raw_parts(buf.as_ptr(), written as usize) };
> +        write!(f, "{}", BStr::from_bytes(b))
> +    }
> +
> +    /// Returns an object that implements [`Display`](core::fmt::Display) for
> +    /// printing the name of a node.
> +    pub fn display_name(&self) -> impl core::fmt::Display + use<'_> {


I don't know about the details but with rustc 1.81 [1] I'm getting [2].
Just doing what is proposed seems to "fix" it:

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 3b1af034e902e..eadf7501d499b 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -26,6 +26,7 @@
 #![feature(const_mut_refs)]
 #![feature(const_ptr_write)]
 #![feature(const_refs_to_cell)]
+#![feature(precise_capturing)]

 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.

Just want to mention it because I think the minimal rustc version we
have to support is 1.78.

Best regards

Dirk

P.S.: Many thanks for working on this! :)

[1]

$ rustc --version
rustc 1.81.0 (eeb90cda1 2024-09-04)

[2]

error[E0658]: precise captures on `impl Trait` are experimental
   --> rust/kernel/property.rs:256:61
    |
256 |     pub fn display_name(&self) -> impl core::fmt::Display + use<'_> {
    |                                                             ^^^
    |
    = note: see issue #123432
<https://github.com/rust-lang/rust/issues/123432> for more information
    = help: add `#![feature(precise_capturing)]` to the crate attributes
to enable
    = note: this compiler was built on 2024-09-04; consider upgrading it
if it is out of date

error[E0658]: precise captures on `impl Trait` are experimental
   --> rust/kernel/property.rs:271:61
    |
271 |     pub fn display_path(&self) -> impl core::fmt::Display + use<'_> {
    |                                                             ^^^
    |
    = note: see issue #123432
<https://github.com/rust-lang/rust/issues/123432> for more information
    = help: add `#![feature(precise_capturing)]` to the crate attributes
to enable
    = note: this compiler was built on 2024-09-04; consider upgrading it
if it is out of date

error: aborting due to 2 previous errors