Maximal size of the field in MariaDB is (max unsigned int) value. Thus, int32_t is not enough, and methods like
virtual int32_t getMaxFieldSize()=0;
virtual void setMaxFieldSize(int32_t max)=0;
have to be changed to
virtual uint32_t getMaxFieldSize()=0;
virtual void setMaxFieldSize(uint32_t max)=0;

This probably can be extended with some naturally unsigned methods, like set of database metadata methods returning version numbers.
uint32_t getDatabaseMajorVersion();
uint32_t getDatabaseMinorVersion();
uint32_t getDatabasePatchVersion();
uint32_t getJDBCMajorVersion();
uint32_t getJDBCMinorVersion();
uint32_t getCDBCMajorVersion();
uint32_t getCDBCMinorVersion();

Then it probably doesn't make sense to leave getMajorVersion() and getMinorVersion() methods in the Driver signed.