请教各位大侠！

Create a new packet descriptor and chain the buffers from the indicated packet descriptor to this new descriptor. This new packet descriptor can then be indicated up to the higher level driver. When this higher level driver returns the packet descriptor, the intermediate driver must unchain the buffers from its packet descriptor, chain them to the packet descriptor it originally received from the underlying driver, and return the original packet descriptor and the resources that it describes to the underlying driver.
怎么理解这段话？摘自Windows2000驱动程序开发大全第一卷P1041 1.3  Intermediate Driver Packet Management
 :)