Hello Linux wireless maintainers, I was testing hostapd 4-address mode and found out the interface of type NL80211_IFTYPE_AP_VLAN is no longer created in recent kernel version. Setup Hostapd version 2.6 Wpa_supplicant version 2.6 Linux kernel 4.19.20 "wds_sta=1" is added in hostapd.conf "iw wlan0 set 4addr on" is set on client side. For kernel 4.14.16, wpa_supplicant connects to hostapd well and hostapd would create wlan0.sta1 interface with type NL80211_IFTYPE_AP_VLAN. The traffic runs well over the AP<---->client. Everything is good. For kernel 4.19.20, wpa_supplicant connects to hostapd well, but hostapd fail to create wlan0.sta1 interface with type NL80211_IFTYPE_AP_VLAN. No traffic is possible between AP and client. GDB shows that when creating wlan0.sta1 interface with type NL80211_IFTYPE_AP_VLAN, kernel return -95 (EOPNOTSUPP) to hostapd. Inside kernel, this - EOPNOTSUPP seems to be returned from nl80211_new_interface()--> nl80211_valid_4addr() which complains WIPHY_FLAG_4ADDR_AP flag is not set. Reading kernel 4.19.20 source, I found that WIPHY_FLAG_4ADDR_AP flag is only possible in simulated hardware. The only place that sets WIPHY_FLAG_4ADDR_AP flag is ieee80211_alloc_hw_nm() The only place that calls ieee80211_alloc_hw_nm() is from drivers/net/wireless/mac80211_hwsim.c So, does it mean that interface with type NL80211_IFTYPE_AP_VLAN will no longer be supported in any real hardware radio? Or I did not understand kernel source right? Please help. For many years, we have been using this 4-address mode interface in our wireless bridge(proprietary mesh) product. To be backward compatible, we have to maintain the same feature in our new product. This 4-address AP<---->client connection is very import to us. Thanks for your help, Chaoxing
