[Click] about userlevel FromDevice

[徐晖]

Hi
I want to capture wireless packet,and write a simple script to have a
test.The script is:
FromDevice(ath0,PROMISC true) -> Print(FromDevice(ath0),HEADROOM true) ->
Discard;
I create a AP in my openwrt system,interface name is ath0.
When I run the click,the resut is not the packet with wireless header,but is
Ethernet packet,
the reslut like:
FromDevice(ath0):   54 (h30 t1992) | 000b6b2f f0f5001f 3ba7c4c3 08004500
00286462 40008006
000b6b2ff0f5 src mac
001f3ba7c4c3 dst mac
0800 type IP
Why?
How can I capture the wireless packet?
Thanks.
-- 
徐晖