[PATCH v5 2/6] rust: pci: add sriov_get_totalvfs() helper

Expose pci_sriov_get_totalvfs() to Rust PCI drivers so they can query
how many SR-IOV VFs a device supports.

Use a conditional C helper because the !CONFIG_PCI_IOV version of
pci_sriov_get_totalvfs() is a static inline function and is therefore
not emitted into the Rust bindings. Return Option<NonZero<u16>> so Rust
callers must handle the zero value that represents unavailable SR-IOV.

Reviewed-by: Alexandre Courbot <[email protected]>
Cc: Alexandre Courbot <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: David Laight <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Zhi Wang <[email protected]>
---
 rust/helpers/pci.c |  8 ++++++++
 rust/kernel/pci.rs | 13 +++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/rust/helpers/pci.c b/rust/helpers/pci.c
index e44905317d75..4ebf256dff23 100644
--- a/rust/helpers/pci.c
+++ b/rust/helpers/pci.c
@@ -24,6 +24,14 @@ __rust_helper bool rust_helper_dev_is_pci(const struct device *dev)
 	return dev_is_pci(dev);
 }
 
+#ifndef CONFIG_PCI_IOV
+__rust_helper unsigned int
+rust_helper_pci_sriov_get_totalvfs(struct pci_dev *pdev)
+{
+	return pci_sriov_get_totalvfs(pdev);
+}
+#endif
+
 #ifndef CONFIG_PCI_MSI
 __rust_helper int rust_helper_pci_alloc_irq_vectors(struct pci_dev *dev,
 						    unsigned int min_vecs,
diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index c6d6bd8f251d..9f19ccd5905c 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -25,6 +25,7 @@
 use core::{
     marker::PhantomData,
     mem::offset_of,
+    num::NonZero,
     ptr::{
         addr_of_mut,
         NonNull, //
@@ -452,6 +453,18 @@ pub fn pci_class(&self) -> Class {
 }
 
 impl<'a> Device<device::Core<'a>> {
+    /// Returns the total number of VFs, or [`None`] if SR-IOV is not available.
+    #[inline]
+    pub fn sriov_get_totalvfs(&self) -> Option<NonZero<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 function returns `unsigned int`, but the value originates
+        // from TotalVFs/driver_max_VFs (which are defined as `u16`), so this cast
+        // cannot truncate.
+        NonZero::new(total_vfs as u16)
+    }
+
     /// Enable memory resources for this device.
     pub fn enable_device_mem(&self) -> Result {
         // SAFETY: `self.as_raw` is guaranteed to be a pointer to a valid `struct pci_dev`.
-- 
2.53.0