Writing Windows WDM Device Drivers

 // Remember fdo in our device extension
 PWDM1_DEVICE_EXTENSION dx = (PWDM1_DEVICE_EXTENSION)fdo->DeviceExtension;
 dx->fdo = fdo;
 …
 // Attach to the driver stack below us
 dx->NextStackDevice = IoAttachDeviceToDeviceStack{fdo,pdo);
 // Set fdo flags appropriately
 fdo->Flags &= ~DO_DEVICE_INITIALIZING;
 fdo->Flags |= DO_BUFFERED_IO;
 …
}
NTSTATUS Wdm1Pnp( IN PDEVICE_OBJECT fdo, IN PIRP Irp) {
 …
 // Device removed
 if (MinorFunction==IRP_MN_REMOVE_DEVICE) {
  // unattach from stack if (dx->NextStackDevice)
  IoDetachDevice(dx->NextStackDevice);
  // delete our fdo
  IoDeleteDevice(fdo);
 }
 return status;
}

Creating Devices

Wdm1AddDevice is called with two parameters, a pointer to the driver object and a pointer to a device object called the Physical Device Object (PDO).

Wdm1AddDevice calls IoCreateDevice to create the Wdm1 device using the parameters described in Table 5.2. The DeviceName parameter can be used to give a name to the device. However, as Wdm1 uses device interfaces, no name needs to be given, so NULL is passed here. Wdm1 devices do not correspond to any of the hardware device types, so FILE_DEVICE_UNKNOWN is given for DeviceType.

Table 5.1 IoCreateDevice function

NTSTATUS IoCreateDevice	(IRQL==PASSIVE_LEVEL)
Parameter	Description
IN PDRIVER_OBJECT DriverObject	Driver object
IN ULONG DeviceExtensionSize	Size of device extension required
IN PUNICODE_STRING DeviceName	Name of device, or NULL
IN DEVICE_TYPE DeviceType	The type of the device: one of the FILE_DEVICE_xxx values listed in the standard header WDM.H or NTDDK.H
IN ULONG DeviceCharacteristics	Various constants ORed together to indicate removable media, read only, etc.
IN BOOLEAN Exclusive	TRUE if only a single thread can access the device at a time
OUT PDEVICE_OBJECT* DeviceObject	The returned device object.

Table 5.2 IoRegisterDeviceInterface function

NTSTATUS IoRegisterDeviceInterface	(IRQL==PASSIVE_LEVEL)
Parameter	Description
IN PDEVICE_OBJECT PhysicalDeviceObject	The device PDO
IN CONST GUID *InterfaceClassGuid	The GUID being registered
IN PUNICODE_STRING ReferenceString	Usually NULL. A reference string becomes part of the interface name and so can be used to distinguish between different interfaces to the same device.
OUT PUNICODE_STRING SymbolicLinkName	The output interface symbolic link name. Do not forget to free the Unicode string buffer using RtlFreeUnicodeString when finished with it.