linux-kernel - Re: [PATCH v2 3/4] rust: pci: impl TryFrom<&Device> for &pci::Device

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Message-ID: <D8LHQSKES3SR.2EW347ONXZ22H@proton.me>
Date: Thu, 20 Mar 2025 23:44:01 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>, bhelgaas@...gle.com, gregkh@...uxfoundation.org, rafael@...nel.org, ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu
Cc: linux-pci@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] rust: pci: impl TryFrom<&Device> for &pci::Device

On Thu Mar 20, 2025 at 11:27 PM CET, Danilo Krummrich wrote:
> @@ -466,6 +466,23 @@ fn as_ref(&self) -> &device::Device {
>      }
>  }
>  
> +impl TryFrom<&device::Device> for &Device {
> +    type Error = kernel::error::Error;
> +
> +    fn try_from(dev: &device::Device) -> Result<Self, Self::Error> {
> +        if dev.bus_type_raw() != addr_of!(bindings::pci_bus_type) {
> +            return Err(EINVAL);
> +        }
> +
> +        // SAFETY: We've just verified that the bus type of `dev` equals `bindings::pci_bus_type`,
> +        // hence `dev` must be embedded in a valid `struct pci_dev`.

I think it'd be a good idea to mention that this is something guaranteed
by the C side. Something like "... must be embedded in a valid `struct
pci_dev` by the C side." or similar.

With that:

Reviewed-by: Benno Lossin <benno.lossin@...ton.me>

---
Cheers,
Benno

> +        let pdev = unsafe { container_of!(dev.as_raw(), bindings::pci_dev, dev) };
> +
> +        // SAFETY: `pdev` is a valid pointer to a `struct pci_dev`.
> +        Ok(unsafe { &*pdev.cast() })
> +    }
> +}
> +
>  // SAFETY: A `Device` is always reference-counted and can be released from any thread.
>  unsafe impl Send for Device {}
>