This message is used by a stream handler to give an empty buffer to the physical device driver. An example would be in an audio recording, where the physical device driver fills the buffer it gets from the stream handler. The pBuffer parameter is a pointer to the buffer to be filled in by the physical device driver. This pointer is either a physical 0:32 pointer, 16:16 far pointer or a global linear pointer. This is defined when the stream handler registers a stream with the device driver using DDCMD_REG_STREAM.
Many devices cannot handle a 0 length buffer. If the driver receives a 0 length buffer, it should not reject the buffer. The driver should do nothing with the buffer and return it in the same order in which it was sent.