Closing a VxD

When you have finished using a VxD, you can close the associated device handle by using the CloseHandle function, or you can let the operating system close the handle when the application terminates. The following example closes a VxD.

CloseHandle(hDevice);

Closing a VxD does not necessarily remove the VxD from memory. If you open a dynamically loadable VxD using the FILE_FLAG_DELETE_ON_CLOSE value, CloseHandle also removes the VxD if no other valid handles are present in the system. The system maintains a reference count for dynamically loadable VxDs, incrementing the count each time the VxD is opened and decrementing when the VxD is closed. CloseHandle checks this count and removes the VxD from memory when the count reaches zero. The system does not keep a reference count for static VxDs; it does not remove these VxDs when their corresponding handles are closed.

In rare cases, you may need to use the DeleteFile function to remove a dynamically loadable VxD from memory. For example, you use DeleteFile if another application has loaded the VxD and you just want to unload it. You also use DeleteFile if you have successfully loaded a VxD by using CreateFile, but the VxD does not support the device IOCTL interface. In such cases, CreateFile loads the VxD but provides no handle to close and remove the VxD. The following example removes the VxD named SAMPLE from memory.

DeleteFile("\\\\.\\SAMPLE");

In this example, SAMPLE is the module name of the VxD. (Do not specify the filename.) Be aware that the module name of a VxD is not necessarily the same as the VxD's filename without a filename extension. In general, avoid using DeleteFile to remove a VxD from memory.