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UserProcessParallelTask

Processes a parallel task in response to a call from the framework.

Declaration

virtual kern_return_t UserProcessParallelTask(SCSIUserParallelTask parallelRequest, uint32_t *response, OSAction *completion);

Parameters

  • parallelRequest:

    A Scsiuserparalleltask object that contains all necessary request information.

  • response:

    A service response for the request.

  • completion:

    An Osaction object that the dext class uses to complete the request.

Discussion

The system calls this method to put a command on the bus, sending all information necessary to process the request in the parallelRequest parameter. Your HBA-specific subclass must implement this method.

The following example shows a minimal implementation of UserProcessParallelTask:

  1. The example starts by using the parallelRequest parameter’s fControllerTaskIdentifier to look up task data, which it stores in a hypothetical convenience type called TaskData.

  2. Next, it sets the metadata for this I/O operation. The kernel generates one long phsyical segment with fBufferIOVMAddr as its start address, as seen here in the call to a hypothetical PrepareScatterGatherList() function. You may need to prepare a custom scatter gather list if your hardware specification requires you to split this up into multiple segments.

  3. After that, the example retains and stashes the completion callback for later.

  4. Finally, the code posts the request to the hardware by calling PostSCSIRequest(), another hypothetical convenience function. Assuming this call returns kIOReturnSuccess, the example sets the response in-out parameter to kSCSIServiceResponse_Request_In_Process, to indicate to the kernel that the request is underway.

kern_return_t
IMPL ( ExampleSCSIDext, UserProcessParallelTask )
{
    kern_return_t     ret          = kIOReturnError;
    TaskData *        taskData     = NULL;

    taskData = ivars->fTaskArray[parallelRequest.fControllerTaskIdentifier];

    // Set all the metadata for this IO.
    taskData->fRequestedTransferCount = parallelRequest.fRequestedTransferCount;
    taskData->fTransferDirection = parallelRequest.fTransferDirection;
    PrepareScatterGatherList ( taskData, parallelRequest.fBufferIOVMAddr );
    …

    // Retain and stash the completion callback.
    completion->retain ( );
    taskData->fAction = completion;
    
    // Submit the request to the hardware.
    ret = PostSCSIRequest ( taskData );
    __Require ( ( kIOReturnSuccess == ret ), Exit );

    // Set the response and return.
    *response = kSCSIServiceResponse_Request_In_Process;

    return ret;
}

See Also

Managing Tasks