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kIOReturnExclusiveAccess
What is being protected
kIOReturnExclusiveAccess means a client already owns an exclusive open on the relevant device or interface. The restriction prevents conflicting commands, state changes, or data paths from being issued by independent clients at the same time. For USB interfaces, Apple documents an exclusive-open path and returns this status when an existing client refuses to release the interface.
This is not a permissions failure. Changing process privileges will not make a second client safe. The resolution is ownership coordination: use the existing service, ask its owner to release the object, select a different interface, or design a broker that serializes requests on behalf of clients.
How to diagnose it
- Identify the process, driver, or system service that owns the interface before attempting a disruptive reset.
- Check whether a kernel driver has claimed the function; user-space USB libraries also expose busy/claim failures for this situation.
- Always pair successful opens with close or release on every error path so an application does not create its own permanent lockout.
- Do not use seize-style APIs as a routine workaround: forcibly taking a device can invalidate another client’s protocol state.
References
- Apple IOReturn.h reference
- Apple USBInterfaceOpenSeize reference
- libusb device lifecycle and interface claims
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