I'm working of functional like USB device filtering. So it adds some restrictions I have to make a decision about plugged device before Start succeeds or fails IOUserClient, as I understood, used for App<->DEXT communication, but not DEXT<->DEXT. Am I right? Conceptually, I need some way to prepare IOService kind of IOResources that starts on DEXT bootstrap and can be reached within the App each time USB device is connected, I need to obtain set of rules to filter particular USB device/interface. This can be achieved by communicating inside DEXT if I could have such mechanism

@Drewbadour , followed your advice. Created for test purposes DEXT with 2 IOServices of IOUserResources kind. Now facing two problems: Somewhy they are launched in separate processes. I.e. after DEXT is loaded, there are two instances of DEXT process, one per IOService. Doy you know what IOPersonalities keys should match to force DEXTs to be loaded as single process? ServiceNotificationReady callback is not called. Example above is replicated accurately. Can you suggest any ideas why?

You can find remote debug details in article: https://medium.com/@alkenso/remote-debug-of-macos-application-using-xcode-1d714d6314bb

@dazy_naoki , adding "import os" resolves issue for me