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Setting properties and registry values

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This guide explains how a Port Class audio driver can set properties and registry values for a PnP device interface. To properly register the device interface and set required values, the Portcls driver must follow these steps:

1. Register the device interface

Before calling PcRegisterSubdevice for the sub-device, the driver should call IoRegisterDeviceInterface to register the KSCATEGORY_AUDIO interface. This allows the driver to set interface properties and registry values before PcRegisterSubdevice registers and enables the interfaces.

When calling IoRegisterDeviceInterface, the audio driver sets the parameters as follows:

  • The PhysicalDeviceObject parameter is the PDEVICE_OBJECT retrieved from the PcGetPhysicalDeviceObject function.
  • The InterfaceClassGuid is set to the interface's class GUID.
  • The ReferenceString is the same as the Name parameter passed to PcRegisterSubdevice.

After completing these tasks successfully, IoRegisterDeviceInterface returns a SymbolicLinkName for the registered interface.

2. Set registry values

The audio driver calls IoOpenDeviceInterfaceRegistryKey to obtain a handle to the device interface registry key. The parameters for IoOpenDeviceInterfaceRegistryKey are set as follows:

  • The SymbolicLinkName is the string returned from IoRegisterDeviceInterface in the previous step.
  • The DesiredAccess is set to KEY_WRITE (or other values if needed by the driver).

After completing these steps, DeviceInterfaceKey returns the opened registry key handle. The audio driver:

  • Calls ZwSetValueKey to set registry values.
  • Closes the registry key handle by calling ZwClose.

Note: If the driver needs to set values in a registry subkey, it should call ZwCreateKey to create the subkey. When preparing to call ZwCreateKey, the driver:

  • Calls InitializeObjectAttributes and sets the ObjectName to the subkey path.
  • Sets Attributes to OBJ_CASE_INSENSITIVE | OBJ_KERNEL_HANDLE.
  • Sets RootDirectory to the handle returned by IoOpenDeviceInterfaceRegistryKey.
  • Calls ZwClose to close any handle created by calling ZwCreateKey.

3. Set properties

The audio driver calls IoSetDeviceInterfacePropertyData to set properties. The parameters for IoSetDeviceInterfacePropertyData are set as follows:

  • The SymbolicLinkName is the string returned from IoRegisterDeviceInterface.
  • The remaining parameters depend on the specific property being set.

See also

Sample Audio Drivers