3

Scenario:
In a nut-shell I am trying to use the existing wlan0 interface on my system, create two virtual interfaces on top of it and use one of them as an access point and the other one as a normal WiFi client.

Problem:
I am able to create the virtual interfaces, see them using iwconfig but only one of them can be brought up using ifconfig. If I try to bring up the other interface I get

SIOCSIFFLAGS: Device or resource busy.

Hardware details:
Xilinx SoC (ARM processor)
Petalinux (Linux Distro)
Intel 8265 NGW (WiFi chipset)

I am quite sure that the Intel hardware supports three modes simultaneously this is the output of iw list | grep -A 2 'interface combination':

valid interface combinations:
                 * #{ managed } <= 1, #{ AP, P2P-client, P2P-GO } <= 1, #{ P2P-device } <= 1, total <= 3, #channels <= 2

This is what I am doing on the terminal:

iw dev wlan0 interface add vwlan0 type managed
iw dev wlan0 interface add vwlan1 type managed

Output of iwconfig

vwlan0    IEEE 802.11  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=0 dBm  
          Retry short limit:7   RTS thr:off   Fragment thr:off  
          Encryption key:off  
          Power Management:on  

vwlan1    IEEE 802.11  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=0 dBm  
          Retry short limit:7   RTS thr:off   Fragment thr:off  
          Encryption key:off  
          Power Management:on  

sit0      no wireless extensions.  

lo        no wireless extensions.  

wlan0     IEEE 802.11  Mode:Master  Tx-Power=22 dBm  
          Retry short limit:7   RTS thr:off   Fragment thr:off  
          Power Management:on  

eth0      no wireless extensions.  

ifconfig vwlan0 up works but
ifconfig vwlan1 up gives
ifconfig: SIOCSIFFLAGS: Device or resource busy

1

I found out by chance that I do not have to bring up the virtual interface I created.

Example

If I execute this statement:

$ iw dev wlan0 interface add vwlan0 type managed

It creates a virtual interface vwlan0 and I can use either hostapd or wpa_supplicant to use it as an access point or WiFi client directly without executing:

$ ifconfig vwlan0 up  

I have to make sure that wlan0 is up and it does the trick.

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