I'm relatively new to IOKit drivers, and after reading through the I/O
Kit Device Driver Design Guidelines and SimpleUserClient example, I
have a few questions about asynchronous I/O with the IOUserClient.
After IOConnectSetNotificationPort has triggered
IOUserClient::registerNotificationPort and a request is later issued
to the kernel with an IOAsyncCallback, does the call immediately
return to the application automatically (like WDM), or do I need to
return from the method as usual? If I need to return as usual, then I
apparently need to start my long-running I/O (e.g. a USB transfer with
a completion callback) and then in that completion get my IOUserClient
to call sendAsyncResult. In this case, complicated asynchronous
operations or PIO don't seem to be options.
Would it be more appropriate to use an IOCommandGate to pass the
asynchronous request to a work loop? The work loop documentation in I/
O Kit Fundamentals seems to indicate that event handlers should not
perform time consuming work, which is at odds with that idea.
Another idea is to spawn a thread to perform the asynchronous I/O.
I haven't been able to find an example of a driver using asynchronous
I/O. If anyone can point me to one that applies best practices, that
would be really helpful.
Thanks,
Dan Wilson
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