Extending the Dispatch Interface
Much of the I/O Manager operation supports a standard Read/Write abstraction. The requestor supplies a buffer and transfer length, and data is transferred from or to the device. Not all devices or their operations always fit this abstraction. For example, a disk format or repartition are requests that are not well-suited to a normal Read or Write operation. Such kinds of requests are handled with one of two extensible I/O function request codes. These codes allow any number of driver-specific operations, without the restrictions of the Read/Write abstraction.
IRP_MJ_DEVICE_CONTROL allows for extended requests from user-mode clients through the Win32 DeviceIoControl call. The I/O Manager constructs an IRP with ...
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