This message is sent to an I/O procedure by mmioRead to request that a specified number of bytes be read from an open file.
LONG lParam1
Specifies a huge pointer to the buffer to be filled with data read from the file.
LONG lParam2
Specifies the number of bytes to read from the file.
The return value is the number of bytes actually read from the file. If no more bytes can be read, the return value is zero. If there is an error, the return value is -1.
The I/O procedure is responsible for updating the lDiskOffset field of the MMIOINFO structure to reflect the new file position after the read operation.
mmioRead, MMIOM_WRITE, MMIOM_WRITEFLUSH