How can I use hostapd to support multiple bssid with usb wifi adapter?

[r96921061 at ntu.edu.tw]

Hi,

I have succeed using hostapd to run multiple bssid with a pci wifi adapter.
However, I used the same config on a usb wifi adapter. The virtual  
wireless interface didn't show up.

Environment:
unbuntu 12.04 with kernel 3.2,
hostapd v0.7.3
usb wifi dongle -
Vendor=0cf3 ProdID=9271 Rev=01.08
Manufacturer=ATHEROS
Product=UB93
Driver=ath9k_htc

Here is my config
=============================================
interface=wlan0
driver=nl80211
ssid=Shamrock
ignore_broadcast_ssid=0
macaddr_acl=0
wpa_psk_file=/etc/hostapd.psk
wps_state=2
ap_setup_locked=1
ctrl_interface=/var/run/hostapd
config_methods=label display push_button keypad
max_num_sta=256
bridge=lbr0
channel=6
wmm_enabled=0
hw_mode=g
ieee80211n=1
ht_capab=[SHORT-GI-20][DELAYED-BA][SHORT-GI-40][MAX-AMSDU-7935][HT40-]
eap_server=1
auth_algs=1
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_passphrase=11111111
wpa_pairwise=CCMP
rsn_pairwise=CCMP
bss=gwlan
bssid=a8:54:b2:15:99:9e
ssid=ShamrockGuest
ignore_broadcast_ssid=0
ctrl_interface=/var/run/hostapd
max_num_sta=256
bridge=gbr
ap_isolate=1
auth_algs=1
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_passphrase=22222222
wpa_pairwise=CCMP
rsn_pairwise=CCMP
=====================================================

And after I execute "hostapd -B /etc/hostapd/hostapd-wlan0.conf"

With pci wifi adapter, I can search the ShamrockGuest and I can see  
below info if I execute "brctl show"

bridge name     bridge id               STP enabled     interfaces
gbr             8000.000000000000       no              gwlan
lbr0            8000.a854b215999f       no              wlan0


However, with usb wifi adapter, I can't search  the ShamrockGuest and  
I also can't see the virtual wireless interface "gwlan" if I execute  
"ifconfig". Besides, I see the below message if I execute "brctl show"

bridge name     bridge id               STP enabled     interfaces
gbr             8000.000000000000       no
lbr0            8000.a854b215999f       no              wlan0

I'll be very grateful if anybody can give me some direction or advise.

Best Regard,
Shamrock