<!--
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    "DriverKit: 19.0 -"
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  "identifier" : "/documentation/USBDriverKit/IOUSBHostDevice/Open",
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  "role" : "Instance Method",
  "symbol" : {
    "kind" : "Instance Method",
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    "preciseIdentifier" : "c:@S@IOUSBHostDevice@F@Open#*$@S@IOService#i#l#"
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  "title" : "Open"
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-->

# Open

Opens a session to a host device.

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

## Parameters

`forClient`

The service object that is opening the session.

`options`

The options to use when opening the session. Specify `0` for this parameter.

`arg`

Additional arguments to the function. Specify `NULL` for this parameter.

## 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 [`IOUSBHostDevice`](/documentation/USBDriverKit/IOUSBHostDevice), and acquires the service’s workloop lock. Child [`IOUSBHostInterface`](/documentation/USBDriverKit/IOUSBHostInterface) objects may open simultaneous sessions, but only one [`IOUSBHostDevice`](/documentation/USBDriverKit/IOUSBHostDevice) object at a time may open a session to the device.

---

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