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kIOFWMessageTopologyChanged
FireWire bus-topology-change message identifies a scoped API or runtime boundary rather than a general machine failure. The message indicates that the FireWire topology changed, commonly around bus reset or device addition/removal; cached node IDs and resources may no longer be valid.
First returning layer
IOKit results, internal tokens, and service messages cross user space, kernel services, and hardware families. Their integer representation does not make their control-flow roles interchangeable.
IOKit return values, internal tokens, and service messages share an integer representation but not the same control-flow meaning. Determine whether the API returns the value or delivers it as a message before treating it as failure. Keep the numeric value, declared return type, and first returning operation together with kIOFWMessageTopologyChanged; the same integer can belong to a different status namespace in another API.
Evidence map
| Capture | Diagnostic value |
|---|---|
| Old/new bus generation, node IDs, GUIDs, channel/bandwidth allocations, and attached services. | Identifies the concrete object and operation associated with FireWire bus-topology-change message. |
| Numeric IOReturn/message value decoded with the matching SDK header. | Separates argument or lifecycle state from the provider beneath this result. |
| Registry generation and first provider/client event before the result. | Creates a stable before-and-after comparison. |
| Known-good device or service state on the same macOS/driver build. | Shows whether this result is the first result or a translated summary. |
Preserve old/new bus generation, node IDs, GUIDs, channel/bandwidth allocations, and attached services before reinstalling, rebooting, clearing state, or substituting another device or provider. A success observed only after such a change is useful comparison data, but it does not identify the original cause.
Change one condition at a time
- Trigger one controlled attach/detach and correlate the topology message with re-enumeration. Keep unrelated inputs fixed so the change remains attributable to this result.
- Change one topology or lifecycle condition while keeping the request payload fixed. Record the first returned status and any state transition observed.
- Verify cleanup and object lifetime after the controlled operation. Treat a changed result as a new boundary rather than automatic resolution of this result.
Decision points
| Observed comparison | Next conclusion to test |
|---|---|
| The first control changes the result | Concentrate on the variable isolated by this check: Trigger one controlled attach/detach and correlate the topology message with re-enumeration. |
| The second comparison for this result reproduces the same first status | Preserve lower-layer provider, driver, service, or runtime evidence before editing application data. The second controlled check was: Change one topology or lifecycle condition while keeping the request payload fixed. |
| A different status replaces this result after the bounded change | The operation moved to another boundary after the third controlled check. That check was: Verify cleanup and object lifetime after the controlled operation. Retain both results and interpret the replacement through its own API contract. |
Repair and regression test
Targeted correction. Invalidate generation-scoped node IDs and rebuild allocations from stable device GUIDs. Modify only the object, argument, policy, provider, or lifecycle state identified by the collected evidence.
Acceptance criterion. Clients re-enumerate once, bind the intended device by stable identity, and stale-generation requests are rejected. Re-run the original operation that produced this result under its original identity and supported configuration, then keep one negative control that still produces the expected neighboring outcome.
Technical references
References for kIOFWMessageTopologyChanged on the deployed platform version.
- Apple XNU: IOReturn definitions — defines the status namespace used.
- Apple: IOKit documentation — documents the API or lifecycle boundary behind this result.
- Apple OSS: XNU source — provides ABI, implementation, or protocol context.
- Apple XNU: FireWire family common definitions — supports the portability and verification limits.
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