# DriverKit Data Types ## Topics ### Data Types [`typedef void (^)(void) IOCallOnceBlock;`](/documentation/DriverKit/IOCallOnceBlock) [`struct IOCallOnceFlag;`](/documentation/DriverKit/IOCallOnceFlag) [`class IOCommand;`](/documentation/DriverKit/IOCommand) [`class IOCommandPool;`](/documentation/DriverKit/IOCommandPool) [`typedef IOCommandPool * IOCommandPoolPtr;`](/documentation/DriverKit/IOCommandPoolPtr) [`typedef IOCommand * IOCommandPtr;`](/documentation/DriverKit/IOCommandPtr) [`class IODMACommand;`](/documentation/DriverKit/IODMACommand) An object that converts memory references to I/O bus addresses. [`struct IODMACommandSpecification;`](/documentation/DriverKit/IODMACommandSpecification) [`typedef int (^)(void) IODispatchAction;`](/documentation/DriverKit/IODispatchAction) [`struct IOHistogramReporter_IVars;`](/documentation/DriverKit/IOHistogramReporter_IVars) [`typedef OSDictionary IOReportLegendEntry;`](/documentation/DriverKit/IOReportLegendEntry) [`struct IOReporter_IVars;`](/documentation/DriverKit/IOReporter_IVars) [`struct IOSimpleReporter_IVars;`](/documentation/DriverKit/IOSimpleReporter_IVars) [`struct IOStateReporter_IVars;`](/documentation/DriverKit/IOStateReporter_IVars) [`enum IOStateReporter_valueSelector : unsigned int;`](/documentation/DriverKit/IOStateReporter_valueSelector) [`struct IVarsInvalidator;`](/documentation/DriverKit/IVarsInvalidator) [`typedef int (^)(const class OSMetaClassBase *, const class OSMetaClassBase *) OSOrderBlock;`](/documentation/DriverKit/OSOrderBlock) [`struct OS_no_retain_t;`](/documentation/DriverKit/OS_no_retain_t) [`struct OS_retain_t;`](/documentation/DriverKit/OS_retain_t) [`typedef uint64_t UInt64;`](/documentation/DriverKit/UInt64) [`typedef uint8_t UInt8;`](/documentation/DriverKit/UInt8) [`typedef unsigned long long malloc_type_id_t;`](/documentation/DriverKit/malloc_type_id_t) [`typedef int (^)(void) IODispatchAction;`](/documentation/DriverKit/IODispatchAction) [`typedef uint16_t IOReportCategories;`](/documentation/DriverKit/IOReportCategories) [`typedef uint32_t IOReportConfigureAction;`](/documentation/DriverKit/IOReportConfigureAction) [`typedef uint8_t IOReportFormat;`](/documentation/DriverKit/IOReportFormat) [`typedef uint8_t IOReportQuantity;`](/documentation/DriverKit/IOReportQuantity) [`typedef uint64_t IOReportScaleFactor;`](/documentation/DriverKit/IOReportScaleFactor) [`typedef uint64_t IOReportUnit;`](/documentation/DriverKit/IOReportUnit) [`typedef uint64_t IOReportUnits;`](/documentation/DriverKit/IOReportUnits) [`typedef uint32_t IOReportUpdateAction;`](/documentation/DriverKit/IOReportUpdateAction) [`typedef void (^)(unsigned long long, class IOService *, unsigned long long) IOServiceNotificationBlock;`](/documentation/DriverKit/IOServiceNotificationBlock) [`class IOServiceNotificationDispatchSource;`](/documentation/DriverKit/IOServiceNotificationDispatchSource) [`typedef libkern::libkern::safe_allocation OSAllocation;`](/documentation/DriverKit/OSAllocation) [`typedef libkern::libkern::bounded_array OSBoundedArray;`](/documentation/DriverKit/OSBoundedArray) [`typedef libkern::libkern::bounded_array_ref OSBoundedArrayRef;`](/documentation/DriverKit/OSBoundedArrayRef) [`typedef libkern::libkern::bounded_ptr OSBoundedPtr;`](/documentation/DriverKit/OSBoundedPtr) [`class OSInterface;`](/documentation/DriverKit/OSInterface) [`typedef OSOrderedSet * OSOrderedSetPtr;`](/documentation/DriverKit/OSOrderedSetPtr) [`class OSOrderedSet;`](/documentation/DriverKit/OSOrderedSet) OSOrderedSet provides an ordered set store of objects. [`typedef type-parameter-0-0 * OSPtr;`](/documentation/DriverKit/OSPtr) [`class OSSet;`](/documentation/DriverKit/OSSet) OSSet provides an unordered set store of objects. [`typedef OSSet * OSSetPtr;`](/documentation/DriverKit/OSSetPtr) [`typedef struct SCSICmd_INQUIRY_PageCx_Header SCSICmd_INQUIRY_PAGECx_Header;`](/documentation/DriverKit/SCSICmd_INQUIRY_PAGECx_Header-c.typealias) [`typedef SCSICmd_INQUIRY_StandardData * SCSICmd_INQUIRY_StandardDataPtr;`](/documentation/DriverKit/SCSICmd_INQUIRY_StandardDataPtr) [`typedef UInt8[16] SCSICommandDescriptorBlock;`](/documentation/DriverKit/SCSICommandDescriptorBlock) [`typedef UInt64 SCSIDeviceIdentifier;`](/documentation/DriverKit/SCSIDeviceIdentifier) 64-bit number to represent a SCSI Device. [`typedef SCSIDeviceIdentifier SCSIInitiatorIdentifier;`](/documentation/DriverKit/SCSIInitiatorIdentifier) 64-bit number to represent a SCSI Initiator Device. [`typedef UInt8[8] SCSILogicalUnitBytes;`](/documentation/DriverKit/SCSILogicalUnitBytes) [`typedef UInt64 SCSILogicalUnitNumber;`](/documentation/DriverKit/SCSILogicalUnitNumber) [`typedef UInt64 SCSITaggedTaskIdentifier;`](/documentation/DriverKit/SCSITaggedTaskIdentifier) 64-bit number to represent a unique task identifier. [`typedef SCSIDeviceIdentifier SCSITargetIdentifier;`](/documentation/DriverKit/SCSITargetIdentifier) 64-bit number to represent a SCSI Target Device. [`typedef uint16_t UInt16;`](/documentation/DriverKit/UInt16) [`typedef uint32_t UInt32;`](/documentation/DriverKit/UInt32) [`typedef struct queue_entry queue_chain_t;`](/documentation/DriverKit/queue_chain_t) [`typedef struct queue_entry * queue_entry_t;`](/documentation/DriverKit/queue_entry_t) [`typedef struct queue_entry * queue_t;`](/documentation/DriverKit/queue_t) --- Copyright © 2026 Apple Inc. 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