how to copy data between two vasurfaces?

[lugui2009]

I have to two vasurfaces,and both have image data with the same format (exactly RGBA). I want to copy data of one vasurface to the other , i only find the way that vaDeriveImage the vasurface ,then use vaMapBuffer,but isn't what I want. I want to copy data between GPU memory.And someone can tell me how to do it ,thank you.