<!--
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    "DriverKit: 19.0 -"
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  "documentType" : "symbol",
  "framework" : "USBDriverKit",
  "identifier" : "/documentation/USBDriverKit/IOUSBHostInterface/Open",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Method",
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    "preciseIdentifier" : "c:@S@IOUSBHostInterface@F@Open#*$@S@IOService#i#*c#"
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  "title" : "Open"
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-->

# Open

Opens a session to the host interface.

```
virtual kern_return_t Open(IOService *forClient, IOOptionBits options, uint8_t *arg);
```

## Parameters

`forClient`

The service object that is opening the session.

`options`

The options to use when opening the session. Specify <doc://com.apple.documentation/documentation/kernel/3143215-anonymous/kusbhostopenoptionselectalternatesetting> to select an alternative setting for this interface immediately. Specify the alternative setting in the `arg` parameter.

`arg`

Additional arguments to the function. If you specify <doc://com.apple.documentation/documentation/kernel/3143215-anonymous/kusbhostopenoptionselectalternatesetting> for the `options` parameter, use this value to specify the value for the alternative setting; otherwise, specify `NULL`.

## Return Value

<doc://com.apple.documentation/documentation/DriverKit/kIOReturnSuccess> on success, or another value if an error occurs. See <doc://com.apple.documentation/documentation/DriverKit/error-codes>.

## Discussion

This method opens a session to the [`IOUSBHostInterface`](/documentation/USBDriverKit/IOUSBHostInterface), and acquires the service’s workloop lock. Only one service at a time may open a session to the interface.

---

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