Re: [PATCH v4] rust: pci: reject IRQ vector indices that do not fit in u32

[Alexandre Courbot]

On Tue Sep 1, 2026 at 10:48 PM JST, Gary Guo wrote:
> On Tue Sep 1, 2026 at 2:32 PM BST, Alexandre Courbot wrote:
>> On Tue Sep 1, 2026 at 8:08 PM JST, Danilo Krummrich wrote:
>>> On Tue Sep 1, 2026 at 12:58 PM CEST, Alexandre Courbot wrote:
>>>> That makes me wonder, shouldn't we make `index` take a `u32` directly?
>>>> If that's what the C API expects, it does make sense to align to it
>>>> instead of forcing users to make a potential unneeded conversion if they
>>>> already have a u32.
>>>
>>> I intentionally did not do this, as the common type for an index is usize. Thus,
>>> I do not expect anyone to already have a u32, but to already have a usize, e.g.
>>> from some iterator.
>>>
>>> The fact that the C API did pick unsigned int as index type is an implementation
>>> detail the abstraction should bother with.
>>
>> Thanks for the clarification (and Miguel for elaborating - I wasn't
>> completely aware of it!). In that case this patch looks correct to me.
>>
>> Note that there is another `as` right after, in the same method:
>>
>>   if irq < 0 {
>>       return Err(Error::from_errno(irq));
>>   }
>>
>>   // SAFETY: `irq` is a valid IRQ number for `self.dev`, resolved from this registration.
>>   Ok(unsafe { IrqVector::new(IrqRequest::new(self.dev.as_ref(), irq as u32), self) })
>>
>>
>> We could get rid of it by replacing the `if irq < 0` test with:
>>
>>   let irq = u32::try_from(irq).map_err(|_| Error::from_errno(irq))?;
>
> I wonder if we can just change kernel::error::to_result to return `Result<u32>`
> instead and have the cast there?

Looks like our messages crossed [1]. :)

Converting `to_result` would require quite a bit of work to update all
the callers, but maybe we can introduce a new variant indeed.

But this makes me think of another step we can take to harden
`to_result`: it should probably warn if the non-error value if not `0`,
as that would indicate the caller needs to consider it.

[1] https://lore.kernel.org/all/DL412XWBP4Y2.K1TH9NELBKPR@xxxxxxxxxx/