Q74810: Calling Windows Functions from a Device Driver

Article: Q74810
Product(s): Microsoft Windows Device Driver Kit
Version(s): 3.0,3.1
Operating System(s): 
Keyword(s): kb16bitonly kbDDK
Last Modified: 03-NOV-1999

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The information in this article applies to:

- Microsoft Windows Device Development Kit (DDK) for Windows, versions 3.0, 3.1 
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SUMMARY
=======

Some device drivers need to call functions provided by the user dynamic- link
library (DLL) of Microsoft Windows. The MessageBox() function is an example of
one of these functions. However, a driver cannot implicitly link to the user
DLL. If a driver attempts to implicitly link to user, it will fail to load and
Windows will not run. The load fails because the drivers are loaded before user
(user requires the drivers). An implicit link to user forces the kernel to load
the user module when the driver is loaded; which Windows cannot do. Therefore,
the driver must establish the link at a later time. This article explains how
this is accomplished.

MORE INFORMATION
================

An example of a driver calling a function in user is the communications driver
(COMM.DRV) which displays a message box to resolve contention on the serial and
parallel ports.

The source code for COMM.DRV is included in the Windows Device Development Kit
(DDK). The driver's Contention_Dlg function displays dynamically links to user
and displays the message box. For Windows 3.1, the Contention_Dlg function is in
the IBMSETUP.ASM file; for Windows 3.0 this function is in the IBMCOM.ASM file.

There are two steps required:

1. Use GetModuleHandle("user") to retrieve the module handle to user.

2. Call GetProcAddress(hUserModule, "MESSAGEBOX") to retrieve the FAR procedure
  address of the MessageBox function.

Use this procedure address to call the function from the driver.

Additional query words: 3.00 3.10 DDKMISC

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Keywords          : kb16bitonly kbDDK 
Technology        : kbAudDeveloper kbWin3xSearch kbWinDDKSearch kbWinDDK300 kbWinDDK310
Version           : :3.0,3.1

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