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kIOReturnStillOpen
An open-lifecycle condition
kIOReturnStillOpen reports that the device is still open. It commonly matters during close, removal, teardown, or a state change that requires all clients to release the provider. IOKit’s device-removal model explicitly coordinates in-flight work and open clients before objects are detached and freed.
Closing one application handle is not necessarily enough if another interface, user client, driver object, or error path retained an open. The correct recovery is to identify the opens and match each successful open or claim with the family’s proper close or release operation. Forceful removal can leave queued requests and ownership state inconsistent.
How to narrow it down
- Track opens, claims, closes, and releases by client and service instance.
- Drain or cancel pending work according to the interface contract before final teardown.
- On physical removal, stop creating new requests and follow removal notifications instead of reusing the prior service object.
- Audit exception and cancellation paths for an unmatched open that persists after normal cleanup.
References
- Apple XNU source: IOReturn.h
- Apple: Managing device removal
- Apple: Introduction to IOKit Fundamentals
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