<!--
{
  "availability" : [
    "DriverKit: 21.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "BlockStorageDeviceDriverKit",
  "identifier" : "/documentation/BlockStorageDeviceDriverKit/IOUserBlockStorageDevice/CompleteIO",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Method",
  "symbol" : {
    "kind" : "Instance Method",
    "modules" : [
      "BlockStorageDeviceDriverKit"
    ],
    "preciseIdentifier" : "c:@S@IOUserBlockStorageDevice@F@CompleteIO#i#k#I#"
  },
  "title" : "CompleteIO"
}
-->

# CompleteIO

Indicates that the dext completed an asynchronous read-write call.

```
virtual void CompleteIO(uint32_t requestID, uint64_t bytesTransferred, kern_return_t IOStatus);
```

## Parameters

`requestID`

An opaque identifier, originally provided in the corresponding [`DoAsyncReadWrite`](/documentation/BlockStorageDeviceDriverKit/IOUserBlockStorageDevice/DoAsyncReadWrite) call.

`bytesTransferred`

The number of bytes transferred.

`IOStatus`

The status of the request.

## Discussion

The dext calls this method to indicate completion of an asynchronous read-write call. Use the `requestID` parameter to determine which [`DoAsyncReadWrite`](/documentation/BlockStorageDeviceDriverKit/IOUserBlockStorageDevice/DoAsyncReadWrite) call resulted in this callback.

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)