On Mon, May 27, 2019 at 12:38 AM Chris Chiu <chiu@xxxxxxxxxxxx> wrote: > The -EBUSY is returned by the ieee80211_check_combinations() in the > ieee80211_check_concurrent_iface() function which is invoked each time > doing ieee80211_open(). > The ieee80211_check_combinations() returns the -EBUSY because of > cfg80211_check_combinations() will iterate all interfaces of different types > then checks the combination is valid or not, which in this case the number > of interface combination accumulated by cfg80211_iter_sum_ifcombos is 0 > when I'm trying to bring up the second station interface. Thanks for clarifying. I see, rtl8xxxu does not provide any iface_combinations so the default is to reject parallel interfaces. Given that we can now confidently say that multiple interfaces are not supported, I think that inside rtl8xxxu_add_interface() you could store a pointer to the vif inside the rtl8xxxu_priv structure (and clear it in rtl8xxxu_remove_interface). Plus for clarity, add a comment pointing out that only a single interface is supported, and make rtl8xxxu_add_interface() acually fail if we already had a non-NULL pointer stored in the priv structure. Then you can simplify the patch to remove the ugly storing of vif inside rtl8xxxu_watchdog. You can store the delayed_work in the main priv struct too, dropping rtl8xxxu_watchdog altogether. Daniel
