IOLog and Interrupt Context

Q:  The documentation for IOLog says "IOLog should not be called from interrupt context." How do I know if I'm running in interrupt context?

A: "Interrupt context" is another name for primary interrupt or hardware interrupt time, as opposed to secondary interrupt or software interrupt time.

There are only two places in I/O Kit you need to worry about running at primary interrupt time. The first is in the Filter function you pass in to IOFilterInterruptEventSource::filterInterruptEventSource. The other, far less common case is in the IOInterruptAction function passed to IOService::registerInterrupt. At these times very little of the system is available so you cannot call IOLog.

The Action function you pass when creating a IOFilterInterruptEventSource will run on the work loop that the event source is attached to, so you can call IOLog in the Action function. Remember, the Action function will only be called if your Filter function returns true or calls IOFilterInterruptEventSource::signalInterrupt.

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