gfs_pio_read - binary stream input
char *gfs_pio_read (GFS_File gf, void * buffer, int size, int * np);
gfs_pio_read() attempts to read up to size bytes from the file
referenced by gf into the buffer starting at buffer, and returns the
number of bytes read to the address pointed by np. On end of file, the
number of bytes read is zero.
NULL The function terminated successfully.
Insufficient memory was available.
Others An error except the above occurred. The reason is shown by its