I/O Model

When Windows sends an I/O request to a WDF driver, the framework receives the request and handles the mechanics of dispatching, queuing, completing, and canceling requests on behalf of its drivers. When an I/O request arrives, the framework determines whether it should handle the request itself or invoke a callback to let the WDF driver handle the request. If the WDF driver is to handle the request, the framework packages the data into a framework request object and passes the object to the driver.

The framework keeps track of every I/O request. Because the framework is aware of all active requests, it can call the appropriate callbacks when an I/O request is canceled, the system's power state changes, the device is removed, and so forth. ...

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