Greetings all, I've got a few design issues with a data-link NKE I'm working on. They all center around thread safety and refcounting. In a nutshell, I have a C++ class whose instances each encapsulate a network interface of interest. Each has a member that holds its associated ifnet*. My plan is to put the dlil_attach_interface_filter() and dlil_detach_filter() calls in the constructor and destructor of these interface objects. In looking at the code in xnu it seems that there is a refcount that will prevent the system from freeing an interface with such an attached filter. And my hope it that this will make it OK for me to hold onto the ifnet* for as long as that filter is in place. Can anyone confirm this? My second question is how to create these objects safely in the first place. Again, cribbing from xnu I've come up with a loop like this: struct ifnet *ifp; // read through list of devices and build a list of adapters that we care about for (ifp = ifnet.tqh_first; ifp; ifp = ifp->if_link.tqe_next) { ... new InterfaceObject( ... ifp ...); } During this section of code I have the network funnel. If I understand correctly, that protects me from any other running thread (even on MP systems). Again, can someone confirm? My real worry is about my own thread's behavior. I understand that kernel threads can block and if they do then I loose and regain the funnel. But since I can avoid making calls that block I can handle that. But what about preemption? If my thread runs out of its time quantum might it get preempted (and again loose and regain the funnel)? And if that happens, couldn't the interface list change while I'm iterating over it? And lastly, whatever the solution to that is ("kernel threads can't be preempted" or "use splnet() / splx()", or something else), what about paths into my NKE that are really user threads that have called into the kernel (through the network stack)? (Can that happen or is everything in the kernel run on a kernel thread with the "call" handled via a kernel thread blocking on a queue?) If it can happen, do I need to consider such threads as different from native kernel threads as far as preemption in my NKE goes? I hate to ask so many questions but I do want to get this right. Any hints would be appreciated. Thanks, Mike _______________________________________________ darwin-kernel mailing list | darwin-kernel@lists.apple.com Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/darwin-kernel Do not post admin requests to the list. They will be ignored.