Using VideoPortGetProcAddress

A video miniport driver developed on one NT-based operating system version can be loaded and run on an earlier operating system version, as long as the miniport driver does not attempt to use functionality that is specific to the newer operating system version.

When the video miniport driver is loaded, the VideoPortGetProcAddress member of the VIDEO_PORT_CONFIG_INFO structure contains the address of a callback routine that the video port driver exports, VideoPortGetProcAddress. A miniport driver can use this callback routine to find the address of a video port function exported from videoprt.sys. After the miniport driver has the function's address, it can use this address to call the function. This is shown in the following example code.


  // Useful typedef for a function pointer type
  //   that points to a function with same argument types
  //   as VideoPortCreateSecondaryDisplay
typedef VP_STATUS ( *pFunc(PVOID, PVOID *, ULONG));

  // Declare a pointer to a function
pFunc pVPFunction;

  // Declare a pointer to a VIDEO_PORT_CONFIG_INFO struct
PVIDEO_PORT_CONFIG_INFO pConfigInfo;

  // Call through VideoPortGetProcAddress callback
  //   to get address of VideoPortCreateSecondaryDisplay
pVPFunction = (pFunc)
  ( *(pConfigInfo->VideoPortGetProcAddress)(
                        pDeviceExt, 
                       "VideoPortCreateSecondaryDisplay")
  );
if (NULL == pVPFunction) {
  // Video port does not export the function
  ...
}
else {
  Status = pVPFunction(DevExtension, 
                      &SecondDevExtension,
                       VIDEO_DUALVIEW_REMOVABLE);
} 

After the call through the VideoPortGetProcAddress callback routine has executed, pVPFunction either is NULL or contains the address of the VideoPortCreateSecondaryDisplay function. If pVPFunction is NULL, the video port driver does not export the function you are trying to find, and the miniport driver must not attempt to use it. If pVPFunction is not NULL, you can use this pointer to call VideoPortCreateSecondaryDisplay as shown in the preceding example.

 

 

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