device: bus_type: Introduce num_vf callback

This allows for bus types to implement their own method of retrieving
the number of virtual functions a NIC on that type of bus supports.
Signed-off-by: NPhil Sutter <phil@nwl.cc>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/device.h

@@ -88,6 +88,8 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *);
  *
  * @suspend:	Called when a device on this bus wants to go to sleep mode.
  * @resume:	Called to bring a device on this bus out of sleep mode.
+ * @num_vf:	Called to find out how many virtual functions a device on this
+ *		bus supports.
  * @pm:		Power management operations of this bus, callback the specific
  *		device driver's pm-ops.
  * @iommu_ops:  IOMMU specific operations for this bus, used to attach IOMMU
@@ -127,6 +129,8 @@ struct bus_type {
 	int (*suspend)(struct device *dev, pm_message_t state);
 	int (*resume)(struct device *dev);
 
+	int (*num_vf)(struct device *dev);
+
 	const struct dev_pm_ops *pm;
 
 	const struct iommu_ops *iommu_ops;