2.1.1 Points to Consider about User I/O Requests

Keep the following points in mind when designing an NT driver:

• NT drivers can be layered, and more than one NT driver can process a single I/O request (IRP).

• NT drivers communicate the success or failure of a requested I/O operation in the I/O status block of the IRP. The I/O Manager communicates the success or failure of a requested I/O operation to a user-mode requestor.

• NT drivers need not and should not be designed to provide application-specific support. A protected subsystem or its subsystem-specific, user-mode drivers supply this kind of support. There is one exception to this rule: an MS-DOS® application that relies on an application-dedicated device can require an NT driver to control the device and a closely coupled Win32 user-mode virtual device driver (VDD). See the Virtual DOS Drivers documentation in the DDK for more information about VDDs..