OS/2 device drivers are used to access the I/O hardware. The IOCtl functions provide a method for an application, or subsystem, to send device-specific control commands to a physical device driver. These IOCtls are subfunctions that are issued through the DosDevIOCtl API function request. The DosDevIOCtl function request can be used only by OS/2 applications; the INT 21h IOCtl request can be used only by DOS applications.

The category and function fields are as follows. Each code is contained in a byte:

Category

Code
0xxx xxxx
OS/2-defined
1xxx xxxx
User-defined
_xxx xxxx
Code.

Function

Code
0xxx xxxx
Return error, if unsupported
1xxx xxxx
Ignore, if unsupported
x0xx xxxx
Intercepted by the OS/2 operating system
x1xx xxxx
Passed to driver
xx0x xxxx
Sends data and commands to device
xx1x xxxx
Queries data and information from device
___x xxxx
Subfunction.

Notice that the send/query data bit is intended only to standardize the function set; it plays no critical role. Some functions can contain both command and query elements. Such commands are defined as sends data.

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