Re: [PATCH v2 1/2] rust: Update PCI binding safety comments and add inline compiler hint

["Danilo Krummrich" <dakr@kernel.org>]

On Fri Jul 11, 2025 at 8:30 PM CEST, Benno Lossin wrote:
> On Fri Jul 11, 2025 at 5:02 PM CEST, Danilo Krummrich wrote:
>> On Thu Jul 10, 2025 at 10:01 AM CEST, Benno Lossin wrote:
>>> On Thu Jul 10, 2025 at 4:24 AM CEST, Alistair Popple wrote:
>>>> diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
>>>> index 8435f8132e38..5c35a66a5251 100644
>>>> --- a/rust/kernel/pci.rs
>>>> +++ b/rust/kernel/pci.rs
>>>> @@ -371,14 +371,18 @@ fn as_raw(&self) -> *mut bindings::pci_dev {
>>>>  
>>>>  impl Device {
>>>>      /// Returns the PCI vendor ID.
>>>> +    #[inline]
>>>>      pub fn vendor_id(&self) -> u16 {
>>>> -        // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
>>>> +        // SAFETY: by its type invariant `self.as_raw` is always a valid pointer to a
>>>
>>> s/by its type invariant/by the type invariants of `Self`,/
>>> s/always//
>>>
>>> Also, which invariant does this refer to? The only one that I can see
>>> is:
>>>
>>>     /// A [`Device`] instance represents a valid `struct device` created by the C portion of the kernel.
>>>
>>> And this doesn't say anything about the validity of `self.as_raw()`...
>>
>> Hm...why not? If an instance of Self always represents a valid struct pci_dev,
>> then consequently self.as_raw() can only be a valid pointer to a struct pci_dev,
>> no?
>
> While it's true, you need to look into the implementation of `as_raw`.
> It could very well return a null pointer...
>
> This is where we can use a `Guarantee` on that function. But since it's
> not shorter than `.0.get()`, I would just remove it.

We have 15 to 20 as_raw() methods of this kind in the tree. If this really needs
a `Guarantee` to be clean, we should probably fix it up in a treewide change.

as_raw() is a common pattern and everyone knows what it does, `.0.get()` seems
much less obvious.