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  · DriverStudio          Automatic Unloading of VxDs
  · DriverBundle
  · Previews              Many applications load VxDs with a call to the Win32
  · Compatibility         API CreateFile. The system recognizes the special
 [Downloads]  ·           string \\.\ at the start of a pathname as an
                          indication of that the call refers to a device, and
 Wizards                  loads the corresponding VxD if it is not already
  · Utilities             loaded. However, developers often find that the VxD
  · NT source             fails to unload when the file handle is closed. There
 examples                 are four common mistakes cause this:
  · VxD source
 examples                   1. The call to CreateFile must specify
  · WDM source                 FILE_FLAG_DELETE_ON_CLOSE in the flags
 examples                      parameter. This tells the operating system that
 [Resources]  ·                it should attempt to unload the VxD when the
 Technical papers              file handle is closed.
  · Useful links            2. The name specified in the call to CreateFile
  · Technical tips             must match the name that appears in the VxDs
 [Support]  ·                  DDB. Occasionally, the file name of a VxD does
                               not match the name given in the macro that
 Support                       declares the DDB (Declare_Virtual_Device).
  · Knowledge base             Without this correspondence, the system fails to
  · Problem                    unload the VxD. Note that the name is case
 submission                    sensitive. It is safest to always use upper case
  · Product                    in the DDB declaration and in the call to
 registration                  CreateFile.
  · Release notes           3. All handles to the VxD must be closed. The
 [Shop NuMega]  ·              system maintains reference counts, so the VxD
 Buy it!                       does not unload until all handles are closed.
  · Price list              4. The VxD must handle control messsage
  · How to buy                 W32_DEVICEIOCONTROL, and must return
  · Sales offices              DEVIOCTL_NOERROR (== 0) when the passed control
                               code is DIOC_CLOSEHANDLE ( == -1). Failure to do
                               this indicates to the operating system that the
 [Y2K Compliance]              VxD did not expect to be closed, so it does not
                               proceed with the unload.

 [More information]       If you avoid the above errors, then a VxD that your
                          application loads by calling CreateFile should
                          automatically unload when you call CloseHandle, or
                          when your application terminates.

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