Function mmc_get_blocksize 

pub unsafe extern "C" fn mmc_get_blocksize(
    p_cdio: *mut CdIo_t,
) -> c_int

Get the block size used in read requests, via MMC (e.g. READ_10, READ_MSF, …) @param p_cdio the CD object to be acted upon. @return the blocksize if > 0; error if <= 0