linux-kernel - Re: [PATCH V6 04/15] rust: device: Add few helpers

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Message-ID: <Z30WgqKCLJbnr0S4@pollux>
Date: Tue, 7 Jan 2025 12:56:50 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Danilo Krummrich <dakr@...hat.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>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pm@...r.kernel.org,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
	rust-for-linux@...r.kernel.org,
	Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
	Erik Schilling <erik.schilling@...aro.org>,
	Alex Bennée <alex.bennee@...aro.org>,
	Joakim Bech <joakim.bech@...aro.org>, Rob Herring <robh@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 04/15] rust: device: Add few helpers

On Tue, Jan 07, 2025 at 04:51:37PM +0530, Viresh Kumar wrote:
> Add from_cpu() and property_present() helpers to the device bindings.

I think you should split this into two separate patches.

> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  rust/bindings/bindings_helper.h |  1 +
>  rust/kernel/device.rs           | 21 +++++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 43f5c381aab0..70e4b7b0f638 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -31,6 +31,7 @@
>  #include <linux/pid_namespace.h>
>  #include <linux/platform_device.h>
>  #include <linux/poll.h>
> +#include <linux/property.h>
>  #include <linux/refcount.h>
>  #include <linux/sched.h>
>  #include <linux/security.h>
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index d5e6a19ff6b7..5bfbc4bdfadc 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -6,6 +6,9 @@
>  
>  use crate::{
>      bindings,
> +    error::Result,
> +    prelude::ENODEV,
> +    str::CString,
>      types::{ARef, Opaque},
>  };
>  use core::{fmt, ptr};
> @@ -59,6 +62,18 @@ pub unsafe fn get_device(ptr: *mut bindings::device) -> ARef<Self> {
>          unsafe { Self::as_ref(ptr) }.into()
>      }
>  
> +    /// Creates a new ref-counted instance of device of a CPU.
> +    pub fn from_cpu(cpu: u32) -> Result<ARef<Self>> {
> +        // SAFETY: It is safe to call `get_cpu_device()` for any CPU number.
> +        let ptr = unsafe { bindings::get_cpu_device(cpu) };
> +        if ptr.is_null() {
> +            return Err(ENODEV);
> +        }
> +
> +        // SAFETY: By the safety requirements, ptr is valid.

There are no safety requirements for from_cpu().

Instead, you should say that the pointer returned by get_cpu_device(), if not
NULL, is a valid pointer to a struct device with a non-zero reference count.

> +        Ok(unsafe { Device::get_device(ptr) })
> +    }
> +
>      /// Obtain the raw `struct device *`.
>      pub(crate) fn as_raw(&self) -> *mut bindings::device {
>          self.0.get()
> @@ -180,6 +195,12 @@ unsafe fn printk(&self, klevel: &[u8], msg: fmt::Arguments<'_>) {
>              )
>          };
>      }
> +
> +    /// Checks if property is present or not.
> +    pub fn property_present(&self, name: &CString) -> bool {
> +        // SAFETY: `name` is null-terminated. `self.as_raw` is valid because `self` is valid.

Maybe "by the invariant of `CString` `name` is null-terminated."?

> +        unsafe { bindings::device_property_present(self.as_raw(), name.as_ptr() as *const _) }
> +    }
>  }
>  
>  // SAFETY: Instances of `Device` are always reference-counted.
> -- 
> 2.31.1.272.g89b43f80a514
>