Re: [PATCH v3 2/8] rust: pci: add sriov_get_totalvfs() helper

["Alexandre Courbot" <acourbot@nvidia.com>]

On Wed Jul 8, 2026 at 11:03 PM JST, Alexandre Courbot wrote:
> On Wed Jul 1, 2026 at 3:26 PM JST, Zhi Wang wrote:
>> Expose pci_sriov_get_totalvfs() to Rust PCI drivers so they can query
>> how many SR-IOV VFs a device supports.
>>
>> Cc: Alexandre Courbot <acourbot@nvidia.com>
>> Cc: Bjorn Helgaas <bhelgaas@google.com>
>> Cc: David Laight <david.laight.linux@gmail.com>
>> Cc: Gary Guo <gary@garyguo.net>
>> Cc: linux-pci@vger.kernel.org
>> Link: https://lore.kernel.org/all/DJHPRE4TGGT8.BUTMYOF5YE05@nvidia.com/
>> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
>> ---
>>  rust/kernel/pci.rs | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
>> index 5071cae6543f..21c51981c02e 100644
>> --- a/rust/kernel/pci.rs
>> +++ b/rust/kernel/pci.rs
>> @@ -450,6 +450,17 @@ pub fn pci_class(&self) -> Class {
>>          // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
>>          Class::from_raw(unsafe { (*self.as_raw()).class })
>>      }
>> +
>> +    /// Returns the total number of VFs, or 0 if SR-IOV is not available.
>> +    #[inline]
>> +    pub fn sriov_get_totalvfs(&self) -> u16 {
>> +        // SAFETY: `self.as_raw()` is a valid pointer to a `struct pci_dev`.
>> +        let total_vfs = unsafe { bindings::pci_sriov_get_totalvfs(self.as_raw()) };
>> +
>> +        // CAST: The C helper returns `unsigned int`, but the value originates
>> +        // from TotalVFs/driver_max_VFs, so this cast cannot truncate.
>
> nit: "from TotalVFs/driver_max_VFs (which are defined as `u16`), ..."
>
> With that,
>
> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

... with an additional item for thought: in a previous revision [1], I
had raised the question of making the return type
`Option<NonZero<u16>>`, as I think it better encodes "0 if SR-IOV is not
available" - callers are then forced to consider the dichotomy of the
result, and not interpret a particular value as having a special meaning.

OTOH, for all practical purposes 0 VFs also seems to be strictly
equivalent to "SR-IOV is not available", so please take this as a
nit to consider, not a blocker.

[1] https://lore.kernel.org/rust-for-linux/DETDILPA1GFY.27WND0TEC5352@nvidia.com/