from usbd_msc.h:72
typedef struct _USBD_STORAGE
{
int8_t (* Init)(uint8_t lun);
int8_t (* GetCapacity)(uint8_t lun, uint32_t *block_num, uint16_t *block_size);
int8_t (* IsReady)(uint8_t lun);
int8_t (* IsWriteProtected)(uint8_t lun);
int8_t (* Read)(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len);
int8_t (* Write)(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len);
int8_t (* GetMaxLun)(void);
int8_t *pInquiry;
} USBD_StorageTypeDef;