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Object Hierarchy

KMDF objects are organized hierarchically. WDFDRIVER is the root object; all other objects are considered its children. For most object types, a driver can specify the parent when it creates the object. If the driver doesn't specify a parent at object creation, the framework sets the default parent to the WDFDRIVER object. Figure 1 shows the default KMDF object hierarchy.

Figure 1

Figure 1 Parent-child relationships among the KMDF objects.

For each object, Figure 1 shows which other object(s) must be in its parent chain. These objects aren't necessarily the immediate parent, but could be the grandparent, great-grandparent, and so forth. For example, Figure 1 shows the WDFDEVICE object as parent of the WDFQUEUE object. However, a WDFQUEUE object could be the child of a WDFIOTARGET object, which in turn is the child of a WDFDEVICE object. Thus, the WDFDEVICE object is in the parent chain for the WDFQUEUE object.

The object hierarchy affects the object's lifetime. The parent holds a reference count for each child object. When the parent object is deleted, the child objects are deleted and their callbacks are invoked in a defined order. Table 3 lists all the KMDF object types.

Table 3 KMDF Object Types




Child list


Represents a list of the child devices for a device.



Describes a list of similar objects, such as resources or the devices for which a filter driver filters requests.



Represents an instance of a device. A driver typically has one WDFDEVICE object for each device that it controls.

DMA common buffer


Represents a buffer that can be accessed by both the device and the driver to perform DMA.

DMA enabler


Enables a driver to use DMA. A driver that handles device I/O operations has one WDFDMAENABLER object for each DMA channel within the device.

DMA transaction


Represents a single DMA transaction.

Deferred procedure call (DPC)


Represents a deferred procedure call.



Represents the driver itself and maintains information about the driver, such as its entry points. Every driver has one WDFDRIVER object.



Represents a file object through which external drivers or applications can access the device.

Generic object


Represents a generic object for use as the driver requires.

I/O queue


Represents an I/O queue. A driver can have any number of WDFIOQUEUE objects.

I/O request


Represents a request for device I/O.

I/O target


Represents a device stack to which the driver is forwarding an I/O request.



Represents a device's interrupt object. Any driver that handles device interrupts has one WDFINTERRUPT object for each IRQ or message-signaled interrupt (MSI) that the device can trigger.

Look-aside list


Represents a dynamically sized list of identical buffers that are allocated from the paged or non-paged pool. Both the WDFLOOKASIDE object and its component memory buffers can have attributes.



Represents memory that the driver uses, typically an input or output buffer that is associated with an I/O request.

Registry key


Represents a registry key.

Resource list


Represents the list of resources that have actually been assigned to the device.

Resource range list


Represents a possible configuration for a device.

Resource requirements list


Represents a set of I/O resource lists, which comprises all possible configurations for the device. Each element of the list is a WDFIORESLIST object.



Represents a counted Unicode string.

Synchronization: spin lock


Represents a spin lock, which synchronizes access to data at DISPATCH_LEVEL.

Synchronization: wait lock


Represents a wait lock, which synchronizes access to data at PASSIVE_LEVEL.



Represents a timer that fires either once or periodically and causes a callback routine run.

USB device


Represents a USB device.

USB interface


Represents an interface on a USB device.

USB pipe


Represents a pipe in a USB interface.

Windows Management Instrumentation (WMI) instance


Represents an individual WMI data block that is associated with a particular provider.

WMI provider


Represents the schema for WMI data blocks that the driver provides.

Work item


Represents a work item, which runs in a system thread at PASSIVE_LEVEL.

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