1#value_indexed 2IOCB_CMD_PREAD 0 3IOCB_CMD_PWRITE 1 4IOCB_CMD_FSYNC 2 5IOCB_CMD_FDSYNC 3 6IOCB_CMD_PREADX 4 7IOCB_CMD_POLL 5 8IOCB_CMD_NOOP 6 9IOCB_CMD_PREADV 7 10IOCB_CMD_PWRITEV 8 11