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kIOReturnLockedRead
A state lock on the read path
kIOReturnLockedRead reports that the device read path is locked. It is more specific than a general busy condition, but the common IOKit code does not identify who imposed the lock or which transition must complete before reads are accepted. The answer depends on the IOKit family and on the operation that established the state.
Do not equate this with unsupported reading: kIOReturnNotReadable means the interface does not support read operations, whereas this result indicates that reading is currently locked. Reopening the object or adding retries without understanding the lock owner can interfere with the operation that is intended to release it.
What to trace
- Record the previous successful state-changing operation and the read request that failed.
- Track open clients, exclusive owners, queue state, and completion events for the same service.
- Use the family’s documented notification or completion mechanism to wait for the lock to clear.
- Handle a persistent read lock as a state-machine or cleanup problem rather than a generic transport timeout.
References
- Apple XNU source: IOReturn.h
- Apple: Introduction to IOKit Fundamentals
- Apple: IOKit architectural overview
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