Mac Dev Center Mac OS X Reference Library Drivers, Kernel, & Hardware: User-Space Device Access I/O Kit Framework Reference

SCSITask.h

Includes:

Overview

SCSITask typedefs and constants used inside the kernel and user space.

Note that the SCSITaskIdentifier is an opaque object and that directly casting the SCSITaskIdentifier to any other type is discouraged. The SCSITask implementation changes when necessary to accomodate architectural changes, performance improvements, and bug fixes.

Device and protocol layer drivers that need to access information contained in a SCSITask should use the appropriate accessor methods in IOSCSIPrimaryCommandsDevice.h or IOSCSIProtocolServices.h

Typedefs

SCSIDeviceIdentifier: 64-bit number to represent a SCSI Device.
SCSIInitiatorIdentifier: 64-bit number to represent a SCSI Initiator Device.
SCSILogicalUnitNumber: 64-bit number to represent a logical unit.
SCSIServiceResponse: Attributes for task service response.
SCSITaggedTaskIdentifier: 64-bit number to represent a unique task identifier.
SCSITargetIdentifier: 64-bit number to represent a SCSI Target Device.
SCSITaskAttribute: Attributes for task delivery.
SCSITaskCompletion
SCSITaskIdentifier
SCSITaskMode
SCSITaskState: Attributes for task state.
SCSITaskStatus: Attributes for task status.

SCSIDeviceIdentifier

64-bit number to represent a SCSI Device.

typedef UInt64 SCSIDeviceIdentifier;

Discussion

If the identifier can either be that of an initiator or a target, SCSIDeviceIdentifier should be used.

SCSIInitiatorIdentifier

64-bit number to represent a SCSI Initiator Device.

typedef SCSIDeviceIdentifier SCSIInitiatorIdentifier;

Discussion

If the identifier is for an initiator only and not a target, then SCSIInitiatorIdentifier should be used.

SCSILogicalUnitNumber

64-bit number to represent a logical unit.

typedef UInt64 SCSILogicalUnitNumber;

Discussion

64-bit number to represent a logical unit.

SCSIServiceResponse

Attributes for task service response.

typedef enum SCSIServiceResponse {  
    kSCSIServiceResponse_Request_In_Process = 0,   
    kSCSIServiceResponse_SERVICE_DELIVERY_OR_TARGET_FAILURE = 1,   
    kSCSIServiceResponse_TASK_COMPLETE = 2,   
    kSCSIServiceResponse_LINK_COMMAND_COMPLETE = 3,   
    kSCSIServiceResponse_FUNCTION_COMPLETE = 4,   
    kSCSIServiceResponse_FUNCTION_REJECTED = 5 
} SCSIServiceResponse;

Constants

kSCSIServiceResponse_Request_In_Process: Not defined in SAM specification, but is a service response used for asynchronous commands that are not yet completed.
kSCSIServiceResponse_SERVICE_DELIVERY_OR_TARGET_FAILURE: The service request failed because of a delivery or target failure.
kSCSIServiceResponse_TASK_COMPLETE: The task completed.
kSCSIServiceResponse_LINK_COMMAND_COMPLETE: The linked command completed.
kSCSIServiceResponse_FUNCTION_COMPLETE: The task management function completed.
kSCSIServiceResponse_FUNCTION_REJECTED: The task management function was rejected.

Discussion

The Service Response represents the execution status of a service request made to a Protocol Services Driver. The Service Response can only be modified by the SCSI Protocol Layer. The SCSI Application Layer can only read the state.

SCSITaggedTaskIdentifier

64-bit number to represent a unique task identifier.

typedef UInt64 SCSITaggedTaskIdentifier;

Discussion

The Tagged Task Identifier is used when a Task has a Task Attribute other than SIMPLE. The SCSI Application Layer client that controls the Logical Unit for which a Task is intended is required to guarantee that the Task Tag Identifier is unique. Zero cannot be used a a Tag value as this is used to when a Tagged Task Identifier value is needed for a Task with a SIMPLE attribute.

SCSITargetIdentifier

64-bit number to represent a SCSI Target Device.

typedef SCSIDeviceIdentifier SCSITargetIdentifier;

Discussion

If the identifier is for a target only and not an initiator, then SCSITargetIdentifier should be used.

SCSITaskAttribute

Attributes for task delivery.

typedef enum SCSITaskAttribute { 
    kSCSITask_SIMPLE = 0, 
    kSCSITask_ORDERED = 1, 
    kSCSITask_HEAD_OF_QUEUE = 2, 
    kSCSITask_ACA = 3 
} SCSITaskAttribute;

Constants

kSCSITask_SIMPLE: The task has a simple attribute.
kSCSITask_ORDERED: The task has an ordered attribute.
kSCSITask_HEAD_OF_QUEUE: The task has a head-of-queue attribute.
kSCSITask_ACA: The task has an auto-contingent-allegiance attribute.

Discussion

The Task Attribute defines how this task should be managed when determing order for queueing and submission to the appropriate device server. The Task Attribute is set by the SCSI Application Layer and cannot be modified by the SCSI Protocol Layer.

SCSITaskCompletion

typedef void ( *SCSITaskCompletion )(
    SCSITaskIdentifier completedTask );

Discussion

This is the typedef for completion routines that work with SCSITaskIdentifiers.

SCSITaskIdentifier

typedef OSObject * SCSITaskIdentifier;

Discussion

This is an opaque object that represents a task. This is used so that drivers for both the SCSI Protocol Layer and the SCSI Application Layer cannot modify the SCSITask object directly but must instead use the inherited methods to do so. This allows the implementation of SCSITask to change without directly impacting device and protocol layer drivers. In addition, it prevents changing of properties that are not allowed to be changed by a given layer.

SCSITaskMode

typedef enum SCSITaskMode { 
    kSCSITaskMode_CommandExecution = 1, 
    kSCSITaskMode_Autosense = 2 
} SCSITaskMode;

Discussion

The SCSI Task mode is used by the SCSI Protocol Layer to indicate what mode the task is executing.

SCSITaskState

Attributes for task state.

typedef enum SCSITaskState { 
    kSCSITaskState_NEW_TASK = 0, 
    kSCSITaskState_ENABLED = 1, 
    kSCSITaskState_BLOCKED = 2, 
    kSCSITaskState_DORMANT = 3, 
    kSCSITaskState_ENDED = 4 
} SCSITaskState;

Constants

kSCSITaskState_NEW_TASK: The task state is new task.
kSCSITaskState_ENABLED: The task is enabled and queued.
kSCSITaskState_BLOCKED: The task is blocked.
kSCSITaskState_DORMANT: The task is dormant.
kSCSITaskState_ENDED: The task is complete.

Discussion

The Task State represents the current state of the task. The state is set to NEW_TASK when the task is created. The SCSI Protocol Layer will then adjust the state as the task is queued and during execution. The SCSI Application Layer can examine the state to monitor the progress of a task. The Task State can only be modified by the SCSI Protocol Layer. The SCSI Application Layer can only read the state.

SCSITaskStatus

Attributes for task status.

typedef enum SCSITaskStatus {    
    kSCSITaskStatus_GOOD = 0x00,    
    kSCSITaskStatus_CHECK_CONDITION = 0x02,    
    kSCSITaskStatus_CONDITION_MET = 0x04,   
    kSCSITaskStatus_BUSY = 0x08,   
    kSCSITaskStatus_INTERMEDIATE = 0x10,   
    kSCSITaskStatus_INTERMEDIATE_CONDITION_MET = 0x14,   
    kSCSITaskStatus_RESERVATION_CONFLICT = 0x18,   
    kSCSITaskStatus_TASK_SET_FULL = 0x28,   
    kSCSITaskStatus_ACA_ACTIVE = 0x30,    
    kSCSITaskStatus_TaskTimeoutOccurred = 0x01,    
    kSCSITaskStatus_ProtocolTimeoutOccurred = 0x02,    
    kSCSITaskStatus_DeviceNotResponding = 0x03,   
    kSCSITaskStatus_DeviceNotPresent = 0x04,   
    kSCSITaskStatus_DeliveryFailure = 0x05,   
    kSCSITaskStatus_No_Status = 0xFF 
} SCSITaskStatus;

Constants

kSCSITaskStatus_GOOD: The task completed with a status of GOOD.
kSCSITaskStatus_CHECK_CONDITION: The task completed with a status of CHECK_CONDITION. Additional information about the condition should be available in the sense data.
kSCSITaskStatus_CONDITION_MET: The task completed with a status of CONDITION_MET.
kSCSITaskStatus_BUSY: The task completed with a status of BUSY. The device server might need time to process a request and a delay may be required.
kSCSITaskStatus_INTERMEDIATE: The task completed with a status of INTERMEDIATE.
kSCSITaskStatus_INTERMEDIATE_CONDITION_MET: The task completed with a status of INTERMEDIATE_CONDITION_MET.
kSCSITaskStatus_RESERVATION_CONFLICT: The task completed with a status of RESERVATION_CONFLICT.
kSCSITaskStatus_TASK_SET_FULL: The task completed with a status of TASK_SET_FULL. The device server may need to complete a task before the initiator sends another.
kSCSITaskStatus_ACA_ACTIVE: The task completed with a status of ACA_ACTIVE. The device server may need the initiator to clear the Auto-Contingent Allegiance condition before it will respond to new commands.
kSCSITaskStatus_TaskTimeoutOccurred: If a task is aborted by the SCSI Protocol Layer due to it exceeding the timeout value specified by the task, the task status shall be set to kSCSITaskStatus_TaskTimeoutOccurred.
kSCSITaskStatus_ProtocolTimeoutOccurred: If a task is aborted by the SCSI Protocol Layer due to it exceeding a timeout value specified by the support for the protocol or a related specification, the task status shall be set to kSCSITaskStatus_ProtocolTimeoutOccurred.
kSCSITaskStatus_DeviceNotResponding: If a task is unable to be delivered due to a failure of the device not accepting the task or the device acknowledging the attempt to send it the device the task status shall be set to kSCSITaskStatus_DeviceNotResponding. This will allow the SCSI Application driver to perform the necessary steps to try to recover the device. This shall only be reported after the SCSI Protocol Layer driver has attempted all protocol specific attempts to recover the device.
kSCSITaskStatus_DeviceNotPresent: If the task is unable to be delivered because the device has been detached, the task status shall be set to kSCSITaskStatus_DeviceNotPresent. This will allow the SCSI Application Layer to halt the sending of tasks to the device and, if supported, perform any device failover or system cleanup.
kSCSITaskStatus_DeliveryFailure: If the task is unable to be delivered to the device due to a failure in the SCSI Protocol Layer, such as a bus reset or communications error, but the device is is known to be functioning properly, the task status shall be set to kSCSITaskStatus_DeliveryFailure. This can also be reported if the task could not be delivered due to a protocol error that has since been corrected.
kSCSITaskStatus_No_Status: This status is not defined by the SCSI specifications, but is here to provide a status that can be returned in cases where there is not status available from the device or protocol, for example, when the service response is neither TASK_COMPLETED nor LINK_COMMAND_COMPLETE or when the service response is SERVICE_DELIVERY_OR_TARGET_FAILURE and the reason for failure could not be determined.

Discussion

The Task Status represents the completion status of the task which provides the SCSI Application Layer with additional information about how to procede in handling a completed task.

The SCSI Architecture Model specification only defines task status values for when a task completes with a service response of either TASK_COMPLETED or LINK_COMMAND_COMPLETE.

Since additional information will aid in error recovery when a task fails to be completed by a device due to a service response of kSCSIServiceResponse_SERVICE_DELIVERY_OR_TARGET_FAILURE, additional values have been defined that can be returned by the SCSI Protocol Layer to inform the SCSI Application Layer of the cause of the delivery failure.

The Task Status can only be modified by the SCSI Protocol Layer. The SCSI Application Layer can only read the status

Enumerated Types

Command Descriptor Block Size
Data Transfer Direction
Untagged Task Identifier

Command Descriptor Block Size

enum {  
    kSCSICDBSize_Maximum = 16,   
    kSCSICDBSize_6Byte = 6,   
    kSCSICDBSize_10Byte = 10,   
    kSCSICDBSize_12Byte = 12,   
    kSCSICDBSize_16Byte = 16 
};

Constants

kSCSICDBSize_Maximum: This is the largest size a Command Descriptor Block can be as specified in SPC-2.
kSCSICDBSize_6Byte: Use this for a 6-byte CDB.
kSCSICDBSize_10Byte: Use this for a 10-byte CDB.
kSCSICDBSize_12Byte: Use this for a 12-byte CDB.
kSCSICDBSize_16Byte: Use this for a 16-byte CDB.

Discussion

Command Descriptor Block Size constants.

Data Transfer Direction

enum {  
    kSCSIDataTransfer_NoDataTransfer = 0x00,   
    kSCSIDataTransfer_FromInitiatorToTarget = 0x01,   
    kSCSIDataTransfer_FromTargetToInitiator = 0x02 
};

Constants

kSCSIDataTransfer_NoDataTransfer: Use this for tasks that transfer no data.
kSCSIDataTransfer_FromInitiatorToTarget: Use this for tasks that transfer data from the initiator to the target.
kSCSIDataTransfer_FromTargetToInitiator: Use this for tasks that transfer data from the target to the initiator.

Discussion

DataTransferDirection constants.

Untagged Task Identifier

enum { 
    kSCSIUntaggedTaskIdentifier = 0 
};

Constants

kSCSIUntaggedTaskIdentifier: This value means the task is untagged.

Discussion

The Untagged Task Identifier is used to indicate no unique tag is associated with the Task.

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Last Updated: 2009-10-15