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

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Message-ID: <Z9ypTc7KysFx2Ykw@cassiopeiae>
Date: Fri, 21 Mar 2025 00:48:29 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: 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, 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 11:44:01PM +0000, Benno Lossin wrote:
> 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.

Sure, sounds reasonable.

> 
> 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 {}
> >  
> 
>