The GetResources routine returns the resources that the PCI Express (PCIe) physical function (PF) requires in order to enable virtualization on a device that supports the single root I/O virtualization (SR-IOV) interface.



void GetVirtualDeviceResources(
  PVOID Context,
  PUINT8 CapturedBusNumbers



A pointer to interface-specific context information. The caller passes the value that is passed as the Context member of the PCI_VIRTUALIZATION_INTERFACE structure for the interface.


A pointer to a caller-supplied variable in which this routine returns a UINT8 value. This value specifies the number of PCIe buses that have been captured for use by the SR-IOV PF of the device.

Return Value

This routine does not return a value.


A PCIe device typically consumes resources on a single PCI bus. The PCI driver assigns a device to a PCI bus by writing the bus number into the Secondary Bus Number register and Subordinate Bus Number register in the upstream bridge port. This port is a PCI-to-PCI bridge within a PCIe root port or a PCIe switch port.

A device that supports the SR-IOV interface may create more virtual functions than can be accommodated on the PCI bus on which the device is connected. In these situations, the upstream bridge port must be configured to capture one or more unused PCI buses. This is done by writing a larger value to the port's Subordinate Bus Number register.

A device that supports the SR-IOV interface must capture PCI buses if at least one of the following is true:

  • The device has more than eight total functions (PFs and VFs) and the device does not support the Alternative Routing Interpretation (ARI) option of the PCI Express 3.0 specification.
  • The device supports ARI and has more than eight total functions, but the upstream bridge port does not support ARI.
  • The device supports ARI and has more than 256 functions, and the upstream bridge port does support ARI.
Note  Regardless of ARI support, each captured bus can support 256 functions.

If the device needs more PCIe Requestor IDs (RIDs) in order to enable all of its VFs, the PCI bus driver does the following:

  1. Writes the device’s bus number into the PCIe Secondary Bus Number register.
  2. Writes a value that is larger than the device’s bus number into the PCIe Subordinate Bus Number register.
The difference between these two register values represents the number of captured bus numbers.

The GetResources routine is provided by the GUID_PCI_VIRTUALIZATION_INTERFACE interface.


Minimum supported client Supported in Windows Server 2012 and later versions of Windows.
Target Platform Desktop
Header wdm.h (include Wdm.h)

See Also