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Using a device interface

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Device interfaces are available to both kernel-mode components and user-mode applications. User-mode code can use CfgMgr32 functions (for example, CM_Get_Device_Interface_List) or SetupDiXxx functions (see SetupDi device interface functions) to find out about registered, enabled device interfaces. The user-mode application can then use I/O APIs such as CreateFile to obtain a handle to the device in order to send I/O to it. To get notified about the enablement and disablement of device interfaces and how to react to those actions, see Registering for notification of device interface arrival and device removal.

Before a kernel-mode component can use a specific device or file object, it must do the following:

  1. Determine whether the required device interface class is registered and enabled.

    A driver can register with the PnP manager to be notified when an instance of a device interface is enabled or disabled. To register, the component calls IoRegisterPlugPlayNotification. This routine stores the address of a driver-supplied callback, which is called whenever an instance of a device interface instance is enabled or disabled, for a specified device class. The callback routines receive the DEVICE_INTERFACE_CHANGE_NOTIFICATION structure, which contains a Unicode string representing the interface instance's symbolic link. See Using PnP device interface change notification for more information.

    A driver or other kernel-mode component can also call IoGetDeviceInterfaces to get a list of all registered, enabled device interface instances for a specific device interface class. The returned list contains pointers to the Unicode symbolic link strings that identify the device interface instances.

  2. Get a pointer to a device or file object that corresponds to an instance of the interface.

    To access a specific device object, the driver must call IoGetDeviceObjectPointer, passing the Unicode string for the required interface in the ObjectName parameter. To access a file object, the driver must call InitializeObjectAttributes, passing the Unicode string in the ObjectName parameter, and then pass the successfully initialized attribute structure in a call to ZwCreateFile.