Writing Layered Drivers
Layered drivers are the most general type of intermediate driver. They depend on a well-defined inter-driver calling mechanism provided by the I/O Manager. The following three sections explain how this mechanism works and what a driver needs to do if it wants to use another driver as a component.
How Layered Drivers Work
As shown in Figure 15.1, a layered driver may expose one or more named Device objects to which clients send I/O requests. When an IRP representing one of these requests arrives, the layered driver can proceed in two different ways.
Send the IRP directly to a lower-level driver.
Hold the IRP in a pending state while it allocates additional IRPs and sends them to one or more lower-level drivers.
If the ...
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