adding virtual interface to wlan0 with iw : "Device or resource busy (-16)"

Question

What I'm trying to achieve:

I'm trying to use my Raspberry Pi 3 as a wifi hotspot.

I'd like to use only wifi to achieve this (I could need it in places where I wouldn't have internet access with ethernet).

So I was following these steps from the archlinux wiki to have both wifi client and wifi access point with a single wifi device.

My current situation :

I checked with iw list :

Wiphy phy0
...
     Supported interface modes:
         * IBSS
         * managed
         * AP
         * P2P-client
         * P2P-GO
         * P2P-device
...
     valid interface combinations:
         * #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
           total <= 3, #channels <= 2
         * #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
           total <= 4, #channels <=
...

My wifi device (the Rpi3 wifi chipset) seems able to handle the Wifi as access point (I managed to make it behave as one and opened a ssh session with it using hostapd and dhcpd).

If I understand this output well, it also supports both AP and client mode.

My Rpi state when the problem occures :

I disabled the hostapd and dhcpd4.service with systemctl, and I shut wlan0 down using ip link set dev wlan0 down.

The actual problem :

Then I tried to add the two virtual interfaces (as root) I got this :

# iw dev wlan0 interface add wlan0_sta type managed addr 12:34:56:78:ab:cd 
command failed: Device or resource busy (-16)     
# iw dev wlan0 interface add wlan0_ap  type managed addr 12:34:56:78:ab:ce
command failed: Device or resource busy (-16)

Same result when trying with phy names or with wlan0 up.

What could I try to solve this?

Answer 1

Actually, it looks like I misunderstood the iw list output.

If the RPI3 chipset was able to behave like this, the two mode it could use simultaneously would be between the same #{...} in the iw list output.

The person helping me on IRC with this also suggested me to use a Wifi dongle to solve this problem.