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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

Object

Type

Description

Child list

WDFCHILDLIST

Represents a list of the child devices for a device.

Collection

WDFCOLLECTION

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

Device

WDFDEVICE

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

DMA common buffer

WDFCOMMONBUFFER

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

DMA enabler

WDFDMAENABLER

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

WDFDMATRANSACTION

Represents a single DMA transaction.

Deferred procedure call (DPC)

WDFDPC

Represents a deferred procedure call.

Driver

WDFDRIVER

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

File

WDFFILEOBJECT

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

Generic object

WDFOBJECT

Represents a generic object for use as the driver requires.

I/O queue

WDFQUEUE

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

I/O request

WDFREQUEST

Represents a request for device I/O.

I/O target

WDFIOTARGET

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

Interrupt

WDFINTERRUPT

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

WDFLOOKASIDE

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.

Memory

WDFMEMORY

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

Registry key

WDFKEY

Represents a registry key.

Resource list

WDFCMRESLIST

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

Resource range list

WDFIORESLIST

Represents a possible configuration for a device.

Resource requirements list

WDFIORESREQLIST

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.

String

WDFSTRING

Represents a counted Unicode string.

Synchronization: spin lock

WDFSPINLOCK

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

Synchronization: wait lock

WDFWAITLOCK

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

Timer

WDFTIMER

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

USB device

WDFUSBDEVICE

Represents a USB device.

USB interface

WDFUSBINTERFACE

Represents an interface on a USB device.

USB pipe

WDFUSBPIPE

Represents a pipe in a USB interface.

Windows Management Instrumentation (WMI) instance

WDFWMIINSTANCE

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

WMI provider

WDFWMIPROVIDER

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

Work item

WDFWORKITEM

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

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