This message is used by a stream handler to give a full buffer to the physical device driver. An example would be the case of audio playback, where the stream handler passes a buffer with data to the physical device driver.
The pBuffer parameter is a pointer to the data buffer. Note that this pointer is either a physical 0:32 pointer, 16:16 far pointer, or a global linear pointer. The pointer type is defined when the stream registers a stream with the device driver (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.